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Mechanised Harvesting of Broadleaved Tree Species in Europe

Mechanised Harvesting of Broadleaved Tree Species in Europe Purpose of the Review The application of cut-to-length (CTL) technology for harvesting and processing timber from broad- leaved tree species is a challenging process, due to thick branches, stem sweep, forks and high wood density. The objective of this review was to describe the current state of harvester use and characterise the effectiveness of mechanised forest operations for broadleaved and mixed forest stands in Europe, paying particular attention to productivity and product quality aspects. An additional aim was to identify the greatest difficulties associated with harvesting broadleaved tree species today and to indicate future challenges and areas for improvement. Recent Findings An interest in wider harvester use for broadleaved tree species started after the storm Lothar in France in 1999. Early experiences demonstrated that lower productivity is common when harvesting broadleaved tree species, due to limitations in delimbing and the high frequency of sweep. Initially, modifications were made to harvester heads, while a newly designed head (CTL 40 HW) was later developed within a European project in 2005–2007. Using various heads, very high productivity was achieved in some cases, but log recovery was unsatisfactory, with large tree tops left without delimbing. The delimbing was of lower quality and log length inaccuracy was observed, as well as economic losses due to damage to plywood caused by feed rollers. These issues resulted in a change in harvester head construction, including work on a patent for a head designed specifically for harvesting broadleaved tree species. Summary The harvester heads that have been developed to date for broadleaved tree species have mainly been used within Central Europe, where the high incidence of broadleaved tree species and their particular morphological features (thick branches and sweep) are a major challenge for CTL technology. There have been many research projects related to this issue: in the last 15 years, there were a few larger initiatives leading to the design and development of harvester heads for broad- leaved tree species, with participation from institutions and universities in France, Germany and Poland. There are currently no ongoing initiatives, but the formation of new ones is strongly recommended because today’s forests have a growing share of broadleaved tree species and are being managed to an increasing extent with CTL technology. Keywords Deciduous tree species · Forest operation · Hardwood · Harvester · Harvester head · Productivity · Thick branch This article is part of the Topical Collection on Forest Engineering * Piotr S. Mederski Department of Forest Utilisation, Faculty of Forestry piotr.mederski@up.poznan.pl and Wood Technology, Poznań University of Life Sciences (PULS), ul. Wojska Polskiego 71A, 60-625 Poznań, Poland * Janine Schweier janine.schweier@wsl.ch Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Andreja Đuka Switzerland andreja.duka@sumfak.unizg.hr Department of Forest Engineering, Faculty of Forestry Petros Tsioras and Wood Technology, University of Zagreb, Svetošimunska ptsioras@for.auth.gr 25, 10002 Zagreb, Croatia Leo G. Bont Department of Harvesting and Technology Forest leo.bont@wsl.ch Products, Lab of Forest Utilisation, Aristotle University Mariusz Bembenek of Thessaloniki, P.O. Box 227, 54-124 Thessaloniki, Greece mariusz.bembenek@up.poznan.pl Vol.:(0123456789) 1 3 2 Current Forestry Reports (2022) 8:1–19 harvesting has become more popular in Europe [15]. In Introduction general, forest operations carried out by harvesters differ among countries in Europe, with a larger share of CTL In contrast to harvester use for forest operations in conifer technology in North, Central and West Europe in com- stands, the use of harvesters in broadleaved forest stands •• parison to South and South-East Europe [15, 16, 17, 18 ]. has a relatively short history. This is because harvesting One reason for this variation is the tree species composi- and processing timber from broadleaved species is more tion–coniferous tree species are more suitable for CTL difficult than from coniferous tree species e.g. spruce and technology and more dominant in North, Central and West pine. Thick branches make it difficult to obtain logs from Europe [15, 19]. However, Scots pine (Pinus sylvestris L.) the top parts of trees, and hardwood trees have higher and Norway spruce (Picea abies (L.) Karst) are conifers wood density than conifers. that are recognised as vulnerable to changing climate con- Besides challenges associated with certain tree spe- ditions, and their abundance in Central European lowland cies, there may be other factors that limit wide harvester forests is expected to decrease significantly with global use, like the low rate of investment capability and fear of change [20]. At the same time, broadleaved tree species unemployment. However, today’s market conditions, with may find the new conditions more suitable; according to low availability of manpower, may accelerate wider use of the latest findings and predictions, European beech and cutting-edge harvesting technology. pedunculate oak (Quercus robur L.) will become (increas- One of the first records of harvester productivity in broad - ingly) dominant in large parts of Central Europe [20]. leaved forest stands was with the harvester type Sifor 614 in Thus, an increasing potential for the use of CTL technol- France in 1993–1996 [1, 2], where European beech (Fagus ogy can be expected, taking into account that the interest sylvatica L.), oak (Quercus sp.), European hornbeam (Carpi- in manual work has declined recently. nus betulus L.), chestnut (Castanea sativa Mill.), birch (Bet- There is a strong need to adapt silvicultural management ula sp.) and aspen (Populus sp.) were harvested. Early use of practices and to provide forest managers with evidence- harvesters was also recorded in the 1990s, in Finland (birch) based recommendations, especially regarding CTL technol- and in Spain (Eucalyptus sp.) [3, 4, 5]. Basically, the use of •• •• ogy [21 , 22 ]. Based on initial studies of the available harvesters for broadleaved species was rather sporadic at literature, it was hypothesised that development of CTL the end of the twentieth century. This changed after wind technology for broadleaved species is an unavoidable step damage resulting from the storm Lothar in 1999, when large in the expansion of forest operations. Therefore, the objec- areas needed clearing and harvesters were a suitable option tive of this study was to assess the current state of harvester in comparison to low-safety motor-manual salvage removal use and characterise the effectiveness of its use for broad- [6]. The need for wider harvester use led to head modifica- leaved tree species in Europe, paying particular attention tions to make timber processing more effective and with to economic (productivity) and product quality aspects. An satisfactory productivity [2]. additional objective was to identify challenges with mecha- Bigot and Cuchet [7] conducted a large study of har- nised forest operations in broadleaved or mixed stands and vester head usability in broadleaved forest stands in France to establish what could or should be improved to enhance and tested 40 harvesters with heads originally dedicated to the efficiency of the timber harvesting of deciduous trees. coniferous species and some adapted for broadleaved tree species. Compared to use with coniferous species, lower productivity was observed and more frequent repairs were Material and Methods needed with broadleaved tree species, which is still true today. In 2004–2005, studies were carried out on harvester An English literature review was conducted in the databases use in coppice chestnut forest stands, and later research Web of Science, Scopus and Google Scholar in April and considered beech and eucalyptus forest stands in Europe May 2021. The following keywords were used to retrieve and North America [8, 9, 10]. Further studies focused on available studies: hardwood cut-to-length; mechanised harvester use in poplar short-rotation plantations [11, 12], harvesting of broadleaves; mechanised harvesting of hard- as well as on improved productivity during multi-stem wood species; mechanised forest operations in mixed stands; processing of spruce and birch [13]. Lower quality wood mechanised forest operations in broadleaved stands; mecha- produced during delimbing, as well as bark shavings, were nised thinning operations in mixed stands; mechanised thin- recognised as useful energy sources. Recently, studies ning operations in broadleaved stands; harvester thinning have indicated that trees with thinner branches in younger operation. stands could be processed efficiently with harvesters [14]. In the first step, no specific time span was chosen in order Meanwhile, cut-to-length (CTL) technology (defined to get a comprehensive basis of relevant studies for the intro- here as harvester use for processing short logs) for timber duction and discussion parts of the article. Titles, abstracts 1 3 Current Forestry Reports (2022) 8:1–19 3 and/or keyword fields were read to decide whether each study conifers in Europe (67%) and the lowest share of broadleaved was related to the topic. In total, 227 studies were identie fi d tree species (16%), with both forest types usually managed using Web of Science, another 327 with Scopus and 229 with as high forests. Broadleaved tree species, especially of the Google Scholar. After excluding studies that were out of scope, younger age classes, are most often used for energy pur- older than 10 years (published before 2011) or double-counted, poses [24, 25]. The average growing-stock density is 129 m −1 a total of 51 studies were considered further to review and ha and is stable: in the last 10 years (2010–2020), it has summarise the current state of CTL harvesting in hardwood increased by 0.8% [23]. stands. CTL technology is widely used in North Europe  [15, •• In a second step, national sources were searched, including 18 ], where strip roads are usually established every 20 m sources in local languages. These included not only magazines to make stands accessible for harvesters. However, a larger dedicated to practitioners, but also websites (e.g. www.w aldw share of mechanised harvesting is present in Sweden and issen. net, which is maintained in German, French, Italian and Finland than in Baltic countries [15, 17]. In the last decade, English) and personal communication between experts and CTL technology applications in broadleaved forest stands the authors of this study. Specifically, the following magazines were mostly carried out in Finland and Latvia and focused were screened: Forsttechnische Information (Germany), Der on birch and alder. In Lithuania, processing with a newly Waldbauer (Austria), Wald & Holz (Switzerland), Drwal designed harvester head was carried out on birch and aspen (Poland), Šumarski list and Nova mehanizacija šumarstva [26]. (Croatia) and FCBA reports (France). Finally, international Few studies from Finland were carried out in stands with and local research projects, dissertations and reports were downy birch (Betula pubescens Ehrh.). One of these studies searched and considered. Additional sources were also con- was focused on the productivity of multi-stem harvesting in sidered based on the expert knowledge of all co-authors. thinning and clear-cut stands dominated by young downy Results were reported according to their geographical birch trees, from which pulpwood and energy wood sec- assignment, distinguishing regions in Europe as North, Cen- tions were processed. The Komatsu 901.4 harvester with tral-West, Central-East, South-West and South-East, with their a Komatsu 350.1 harvester head was used with an option respective countries (Table 1) [23]. References were structured for multi-stem harvesting [25]. Tree-specific time studies according to the region and based on four important aspects were conducted, and productivity models based on these related to CTL hardwood harvesting: productivity and cost, investigations were elaborated for multi-stem cutting. product quality (timber assortments), delimbing quality and Clear-cutting in older stands resulted in a higher cutting utilisation of tree stems for timber assortments. However, the productivity than in younger stands where thinning was sections might differ slightly depending on the regions’ char - carried out. Multi-tree cutting was more productive, but acteristics and the relative importance of challenging factors only marginally and in both types of stands. This was due studied in the local conditions. to the small share of multi-stem cutting. Harvesting condi- tions were more favourable in clear-cutting than in thinning Results and Discussion operations. The multi-tree harvesting productivity was from 3 −1 5.6 to 17.4 m PMH (productive machine hour without 3 −1 Overview delays) in clear-cut stands and from 4.8 to 10.9 m PMH in thinned stands. In terms of multi-tree cutting, the har- The forest cover and tree species composition of forests in vester head processed only 1.2 trees per cycle in clear-cut Europe vary across the regions (Table 1). The most forested stands and 1.1 trees per cycle in thinning stands. Finally, region is North Europe, which also has the largest share of it was concluded that improving harvesting equipment for coniferous tree species. However, the highest growing-stock multi-tree cutting of birch and other tree species that have density is in Central-East Europe. Broadleaved tree species stems with sweep is necessary. occur in all regions, with South-West Europe having the largest In another study from Finland, downy birch harvesting share of forest stands with deciduous tree species (Table 1). was carried out in young (age 12 to 29 years) forest stands [24]. A Valmet 911.3 harvester was used for cutting with an engine power of 170 kW. The harvester was equipped with Experiences with Harvesting Broadleaved the Bracke C16.b accumulating felling head fitted with a Tree Species circular saw disc. A small volume of trees harvested with clear-cutting methods led to satisfactory productivity, from 3 −1 North Europe 6 to 24 m PMH , in spite of harvesting residues of ca. 7% of the total biomass that were left on the harvesting sites. In North Europe, about 54% of the land area is forested In a final research from Finland, the impact of the remain- (71.299 mln ha), and this region has the largest share of ing young spruce understorey on the cutting productivity in 1 3 4 Current Forestry Reports (2022) 8:1–19 1 3 Table 1 Main characteristics of forest management in the five European regions [23] Selected feature North Europe Central-West Europe Central-East Europe South-West Europe South-East Europe Countries in the region Denmark, Estonia, Finland, Austria, Belgium, France, Belarus, Czech Republic, Andorra, Holy See, Italy, Albania, Bosnia and Herze- Iceland, Latvia, Lithuania, Germany, Ireland, Liech- Georgia, Hungary, Poland, Malta, Monaco, Portugal, govina, Bulgaria,Croatia, Norway, Sweden tenstein, Luxembourg, Neth- Republic of Moldova, Spain Cyprus, Greece, Montenegro, erlands, Switzerland, UK Romania, Slovakia, North Macedonia, Serbia, Ukraine Slovenia, Turkey Forested land area, % 53.8 27.9 27.3 35.5 31.5 Average growing-stock den- 129.0 242.1 254.6 59.7 115.7 3 −1 sity, m ha Growing stock:   broadleaves, % 25.6 44.9 47.4 44.4 53.1   conifers, % 74.4 55.1 52.6 55.6 46.9 Growing stock trend (annual +0.80 +1.06 +1.58 +1.06 +1.74 growth in 1990–2020), % Management system High forest High forest High forest High forest High forest Coppice with standards Coppice with standards Coppice Coppice Distance between strip roads/ 20 20–40 20 or 30 Depends on terrain conditions Depends on terrain conditions skid trails, m Size of clear-cuts, ha The most common is 4–10 Small, 1–2 4–6 Small, 1–3 Small, if feasible Share privately owned f orest Large Large Medium Large Small, apart from Slovenia >75% and Serbia 47% Dominant harvesting sy stem Fully mechanised Partially mechanised Partially mechanised Partially mechanised Partially mechanised All countries in the region; countries with studies considered suitable for this paper are given in bold High forest originating from seeds or planted seedlings, in contrast to coppice forest In Sweden, larger area of clear-cuts can be >20 ha; however, any application for clear cut >0.5 ha has to be approved by Forest Agency Large, medium and small share, understood as >50%, 25–50% and <25% privately owned forests, respectively Fully mechanised and partially mechanised, understood as min. 70% and min. 30%, respectively, of timber being cut with a harvester-forwarder system Current Forestry Reports (2022) 8:1–19 5 thinning stands dominated by downy birch was investigated forest, which can be even-aged management, continuous [27]. Tests were carried out on 50- to 75-year-old birch trees cover forestry or uneven-aged forestry. One exception is with a mean diameter at breast height (DBH) from 14 to France, which has a large share of broadleaved tree species 24 cm. A medium-sized John Deere 1070/745 with a boom (64%) and where around 30% of the total forest area is tra- reach of 10 m was used in the study. Different productivi- ditionally managed as coppice with standards [30]. A large 3 −1 ties were achieved from 13 to 29 m PMH . In particular, share of the forest area in CW Europe is managed using for- 3 −1 productivity was 15–29 m PMH in thinning stands where est strip roads with 20- to 40-m distance between them, and 3 −1 there were no spruce trees present, 14–24 m PMH in with restrictions limiting penetration by any machine in the stands where spruce trees were present but were not consid- zone between the strip roads. Again, France is an exception, 3 −1 ered, and 13–21 m PMH in stands where spruce under- as it doesn’t make use of a defined strip road network [31]. growth was retained. Since clear-cuts are usually tolerated for small areas only In Latvia, grey alder is an important tree species in the in CW Europe (e.g. <1 ha in Germany, <2 ha in Austria), management of non-state forests. Motor-manual felling is a the dominant harvesting system is selective cutting, which is common method in non-state forests, but fully mechanised conducted in a motor-manual system, partially mechanised forest operations are carried out in final felling. Liepiņš system (i.e. motor-manual felling and mechanised process- et al. [28] examined the effectiveness of motor-manual and ing) or fully mechanised system. The choice depends on the mechanised harvesting, in which productivity reached 2.99 strip road density but also on the forest ownership. There 3 −1 and 7.04 m PMH , respectively. In spite of the lower pro- is a large share of privately owned forests (almost 75% in ductivity, motor-manual harvesting was more cost-effective France, approx. 50% in Austria and Germany). Owners are than mechanised forest operations. It was also concluded responsible for small forest areas only and do not make that improvements in work organisation that could lead to large investments. The trend to use light and less special- higher productivity and a potential increase in labour costs ised machines can be observed in coppice forests as well, in the near future may increase the financial competitiveness which is consistent with the rural and small-scale character of mechanised harvesting. of coppice forestry [30]. The majority of fully mechanised It was reported that the average cost for final felling in felling operations are carried out by contractors e.g. approx. Latvia, including cutting, off-road transport and further 90% in Germany [32]. In hardwood stands, the share of fully −3 transportation to the customer, reached 16.54 € m in 2015 mechanised harvesting operations is only about 10–20%. [29]. For these three specific operations, the calculated costs Schuldt [33] assessed the status of partially and fully mech- −3 were similar at 5.70, 4.94 and 5.90 € m , respectively [17]. anised harvesting methods for hardwood stands, thereby −3 In thinning operations, the average cost was 21.60€ m but focusing on a medium DBH of 20–35 cm. He recognised −3 was more differentiated: 9.39, 6.14 and 6.07 € m , respec- that a machine with at least a medium-sized engine power tively [17, 29]. Differences in harvesting costs depended is needed and that it should be run by a skilled operator. mostly on the type of felling (thinning or final felling) but Smaller harvesters were not considered suitable because also on forwarding conditions, such as soil bearing capacity they have a shorter boom reach and thus require a denser and forwarding distance. However, there was no evidence network of strip roads, as confirmed by Mederski et al. [34 ]. that tree species composition had a significant impact on Selected studies included in this paper were from Austria, harvesting costs. France, Germany and Switzerland. A study on product quality was carried out on birch and Labelle et al. [35] conducted a pilot study consisting of aspen in Lithuania and indicated that keeping a stable length 82 sample plots in a 4.5-ha beech-dominated mixed stand in of logs is a challenge for harvesters. Zinkevicius et al. [26] Germany, aiming to assess the influence of silvicultural man- reported that, for birch and aspen logs, the length accuracy agement (selective-cut vs clear-cut) and tree species (spruce of cut logs by a motor-manual operator was better than the vs beech) on the performance of the analysed harvester. The accuracy of bucking by the CTL 40 HW harvester head stand had an average age of 90 years and an estimated vol- 3 −1 designed specifically for broadleaved tree species. ume of 280 m ha . A six-wheeled single-grip harvester was used for the felling operation (2005 TimberPro 620-E Central‑West Europe equipped with a LogMax 7000C harvester head). The result- 3 −1 ing felling productivity for beech trees was 24.7 m PMH 3 −1 3 −1 In Central-West (CW) Europe, about 28% of the land area (23.4 m PMH in selective-cut and 27.5 m PMH in 0 0 is forested (38.966 mln ha) [23]. The average growing-stock clear-cut). This was, however, 31–45% lower than the pro- 3 −1 3 −1 3 −1 density is 242 m ha , whereas Switzerland (354 m ha ), ductivity observed in spruce stands (33.9 m PMH in 3 −1 3 −1 3 −1 Germany (321 m ha ) and Austria (299 m ha ) represent selective-cut and 36.0 m PMH in clear-cut). Processing the upper limit. Overall, the growing stock is increasing in was more time consuming in selective-cut compared with this region. The most common management system is high clear-cut operations, due to larger tree diameters (DBH 41 1 3 6 Current Forestry Reports (2022) 8:1–19 cm vs 32 cm). In another pilot study, [36 ] observed four observed for larger diameters: the productivity increased to 3 −1 3 harvesters (two-wheeled and two-tracked machines) that 14 m PMH at a stem volume of 0.20 m . The multi- worked in four different plots with a high percentage of stem structure did not result in technical problems or a sig- large-diameter trees (oak, European beech). Two operations nificantly greater time consumption for the harvester, even were conducted on a fully mechanised basis and processing though it was slightly more time-consuming to grab and fell was the most time-consuming step, taking 54–65% of the multi-stemmed trees than single-stemmed trees. Compared time per cycle. The harvesting productivity varied between with manual felling, the harvester left significantly (5 cm) 3 −1 29 and 43 m PMH on average. taller tree stumps, although [42] showed that mechanised In France, the mechanised processing of logs from large cutting does not seem to have any negative effects on cop - crowns of broadleaved species is of particular interest. Ruch pice regeneration and growth. et al. [37] compared two harvesting systems, the first with Fully mechanised hardwood harvesting depends mainly a grapple saw that was attached to a forwarder and the sec- on the harvester head or the fuelwood feller unit. Using soft- ond with the grapple saw that was attached to an excavator wood harvester heads in hardwood stands is technically dif- which processes the crowns for a forwarder. The one- and ficult. Nordic products are light and handy, but felling heads two-machine systems were analysed in terms of productiv- have been constructed for tree species with less dense wood ity, efficiency and technical and economic aspects. Nine key [43]. On the other hand, North American felling heads are factors influencing productivity were identified. The authors more robust and powerful but must be mounted on heavy concluded that (i) the grapple saw is an easy-to-use piece machines, which stands in conflict with soil protection issues of equipment which is efficient and requires a comparably and Central European silvicultural practices [44]. Chakroun small investment for the contractor (15,000 €), and (ii) the et al. [44] performed a study in which two recently devel- single-machine system performs best, with costs varying oped fuelwood feller units from French manufacturers were −1 −1 between 8 and 14 € t , compared with 20 to 23 € t for a compared in typical hardwood biomass forests: (a) thinning two-machine system. Several studies (e.g. [38]) have been in regular high forest and (b) clear-cutting in coppices. The conducted in France to observe the current productivity of feller units were tailored for the tree species available in applied hardwood harvesting systems. These studies indi- Central and South Europe, allow multi-tree handling, and cated that there was a significant increase in the produc- were designed to be mounted on medium-sized excavators. tivity of the machines involved in hardwood harvesting in The main findings of the study were that the significant fac - recent years (around +22.7% from the period of 2000–2007 tors influencing productivity were tree size and stand type to 2008–2015) but that the rate of mechanisation of hard- (with productivity generally higher in high forests), with 3 −1 wood cuts remains low (but increased from 10% in 2013 values ranging from 5.7 to 17.1 m PMH . to around 15% in 2018) [39]. The technical complexity of Kleinschmit [45] aimed to determine the economically dealing with the most poorly shaped hardwoods, combined optimal processing intensity of beech crowns in Germany. with the absence of an ideal harvester head, could explain He conducted trials with highly mechanised systems this observation. using a John Deere harvester 1270E IT4 with a Waratah Mechanised harvesting of hardwoods is mainly carried felling head H480C developed for timber of large dimen- out by not only harvesting machines in CW Europe, but also sions. Kleinschmit examined the processing of beech trees by modified excavators equipped with harvester heads [40]. and presented a decision model with the aim not only of As there is no specific harvesting machine dedicated to hard- explaining the economic relationships of crown processing, woods, a lower annual volume was harvested in broadleaved but also of assisting decision makers in determining the 3 −1 −1 stands, i.e. 14,000 m year machine , compared with economically optimal processing intensity or the economi- 3 −1 −1 23,500 m year machine observed in softwood stands cally optimal top diameter and raising their awareness of the in France [40]. cost dependencies in the case of changed economic frame- Even though less important than high forests, traditional work conditions. Branches with a >7 cm over-bark diameter (and partially modern) coppice forests play a role in CW could be identified as cost drivers. These branches require Europe. Machines larger than traditional forestry tractors are additional time consumption of about 24 s just for cutting. increasingly being used for coppice felling and processing Processing logs with branches took five times longer than [30]. Suchomel et al. [41] determined the technical feasi- processing logs with the same length but from tree parts bility and the time consumption of harvesting oak coppice without branches. with an average DBH of 17.5–18.2 cm. They investigated Cacot et  al. [46] performed a study on a new type of an HSM 405H 6WD harvester with a CTL 40HW harvester delimbing tool for hardwood trees in France: oak, chestnut, 3 −1 head and found an overall productivity of 9.5 m PMH birch and aspen. The focus was on the shape of the delimb- for trees with a DBH >10 cm and an average stem volume ing knives modified by the integration of ribs in the cutting of 0.17 m . The main advantage of the studied harvester was area. In a first step, several types of knives were compared 1 3 Current Forestry Reports (2022) 8:1–19 7 in the laboratory in terms of the energy required for cutting. the distribution of the strip road network is irregular and Based on this evaluation, two harvester heads, each equipped depends mainly on the land configuration. with one fixed and two mobile ribbed knives (John Deere The dominant harvesting system in CE Europe is selec- 752 HD, Kesla 25 RH harvester head), were compared with tive cutting, which is used in all premature stands. Clear-cuts the original knives over 1 year. Using the ribbed knives led are usually applied on a maximum area of 4 ha, with the to an increase in productivity by 21% in the delimbing pro- exception of 6 ha in Poland. CTL technology used during cess, although the increase in overall productivity could not thinning and final felling covers 38% of the total harvest- •• be proven statistically. ing in the Czech Republic and 40% in Poland [18 , 49, For several reasons (e.g. work safety, salvage logging, 50], compared with only 5% in Slovakia and 2% in Roma- lack of own personnel), some state forest administrations nia [17]. In CE Europe, CTL technology is used mainly for and federal research institutes within CW Europe actively coniferous species, but harvesters can be used for broad- •• promote fully mechanised hardwood felling. The Austrian leaved species as well, such as birch [51, 52 ], oak [53], •• Research Centre for Forests (BFZ), for instance, published alder [54, 55] and aspen and poplar [56, 57 ]. However, a video [47] in which they state that a major challenge is broadleaved species can be seen as a factor limiting har- the undergrowth and argue that the basic requirement for a vester use in CE Europe, including in mountainous areas successful operation is good visibility of the strip roads, the [15]. Taking into account the distribution of harvesters and future crop trees and the trees selected for removal. the share of broadleaved species in the analysed region, it The potential for future mechanised hardwood harvest- can be concluded that ca. 10–15% of hardwood timber in ing in CW Europe is significant. In recent years, France Poland is obtained by harvesters, while in other countries, seemed to be very active in developing and testing solutions such as the Czech Republic, Slovakia, Romania and Hungry, for mechanised harvesting of hardwood species. This can timber from broadleaved stands is rarely produced with fully be explained mainly by its forest structure. Current trends mechanised technologies. show that companies are reacting to the demands of practi- Studies on the productivity of harvesters when process- tioners. This development is also driven in part by climate ing the timber of broadleaved species have shown that it change [48] and its associated impacts (e.g. dying ash and may differ from values for harvesting coniferous trees in beech trees). In Switzerland, a fully commercial technical CE Europe. In earlier studies carried out by Mederski et al. solution was designed and constructed to safely and effi- [58] in Poland, harvester thinning operations in broadleaved ciently fell hardwoods, including large trees, that might be mixed stands (mainly birch) resulted in a productivity of 3 −1 dry or affected by illness. In this solution, a safety platform 13.40 m PMH . This study was based on a harvester head is mounted on a felling excavator with a 15-m boom using specially designed and built for broadleaved species: CTL a quick-change system. The trees are held by the excavator 40HW. A much higher productivity was achieved when har- grapple during the felling operation and the safety platform vesting 46- and 61-year-old birch with a Sampo Rosenlew then encloses the stem and protects the feller from falling 1066 and Keto 150LD head [51]. In the study, productiv- −1 branches and crown parts. After the feller has left the area ity reached 26.95 and 40.46 PMH in younger and older of danger, the tree is safely moved by the excavator in the stands, respectively, and was higher by 44% and 41%, desired felling direction [personal communication with respectively, in comparison with productivities achieved Weber, 2021]. when harvesting pine of the same age. These differences were mainly due to tree size (birch had a larger volume) and, Central‑East Europe of considerable importance, to the fact that birch logs with a diameter over bark of up to 12.3 and 16.2 cm were processed In Central-East (CE) Europe, 27.3% of the land area is in younger and older stands, respectively. In comparison, covered with forest (44.735 mln ha), with broadleaved and processing of pine was more effective for log diameters of coniferous stands summing to ca. 40% each and mixed up to 9.4 and 10.6 cm over bark in younger and older stands, stands to ca. 20% [23]. CE Europe is the richest area in respectively [51]. 3 −1 terms of growing stock, at 254.6 m ha , with the high- In another study using a large pool of data in Poland 3 −1 3 −1 est values in Romania (339.8 m ha ), the Czech Repub- [59], the mean productivity of 15.77 m PMH when har- 3 −1 3 −1 lic (295.4 m ha ) and Poland (287.9 m ha ) [23]. The vesting broadleaved species was lower than the productiv- majority of areas are managed in the form of high forest as ity achieved in pine stands, which varied from 18.57 m −1 3 even-aged and uneven-aged stands. Coppice forests are rare PMH in younger stands (41–60 years old) to 22.60 m −1 and tend to be grown as coppice with standards. Stands are PMH in older stands (81–100 years old) [19]. In other accessible by machines with networks of strip roads, with studies in Poland, in which a Ponsse harvester was used with 3 −1 a distance between them of 20 m for harvesters and ca. 30 head H7, the productivity of oak was 20.32 m PMH for m for skidders. Exceptions exist in the mountains, where harvested trees with a mean DBH of 20.0 cm and 0.25 m 1 3 8 Current Forestry Reports (2022) 8:1–19 of timber was harvested from one tree on average [53, 60]. harvesters for felling and processing timber of the four most The interesting aspect of this study was the use of tree trunks common and economically important broadleaved species for logs. It was demonstrated that the mean top diameter in the country: oak, beech, birch and alder. All tests were over bark of the last log (from the highest tree part) was carried out in 40- to 80-year-old stands. Harvesters of 11 13.3 cm when attempting to process logs up to the smallest different producers were tested with 11 different heads. Tri - diameter of 7.0 cm over bark. It was also confirmed that the als were carried out on 60 sample plots in North Poland and top diameter of the last log depended on the DBH of the tree the considered parameters of harvester efficiency were the from which that log was obtained. It is a challenge to make following: (1) productivity, (2) cost, (3) range of trunk utili- harvesting small trees profitable. A study on harvester use in sation for logs, (4) length accuracy, (5) quality of delimbing an 8-year-old poplar plantation in Poland showed that pro- and (6) damage to logs. Considering all of these param- 3 −1 ductivity reached 7.5 m SMH (scheduled machine hours, eters, the best results were achieved when a Waratah head with delays) when the multi-tree harvesting mode was used was used, although good results were also obtained with 3 −1 •• and 6.5 m SMH in single-stem processing [57 ]. heads by Ponsse and Valmet. The average productivity was 3 −1 The quality of delimbing was studied extensively by Mederski 15.77 m PMH in all analysed stands, with maximum 3 −1 [51] in a comparison of pine and birch logs. The two tree species productivity reaching 36.16 m PMH in oak stands with were analysed separately in two mixed stands in Poland with a mean DBH of 28 cm. Generally, higher productivity was ages of 46 and 61 years. Testing of the quality of delimbing was achieved in alder stands, where larger trees were harvested. carried out as measurements of stubs left after delimbing with a It was also discovered that tree tops with larger diameters Keto 150LD head. The largest stubs were observed on the birch (in comparison to coniferous species) are typically left, as logs from older trees, with a mean stub length of 34 mm, while a result of difficulty delimbing in tree crowns. Overall, the on the birch logs from the younger stand, the mean stub length completed project popularised harvester use for broadleaved was only 26 mm. On the pine logs, the stubs were significantly species in Poland and convinced forest owners and forest smaller: 13 and 12 mm on logs from older and younger trees, entrepreneurs to consider wider harvester use in broadleaved respectively. Within this study, the accuracy of log length was or mixed stands. also considered, and it turned out that the cross-cutting accuracy The CTL 40HW harvester head, developed in 2005–2007 was highest for the butt ends of the older pine stand (more than within the ForstINNO project, was a new harvester head 60% of the logs had a very narrow length tolerance set in the dedicated to broadleaved species and tested in CE countries. harvester computer: 2.53–2.55 m). The least accurately cut logs The CTL 40HW was designed to cut trees with a maximum within this category were the top pine assortments obtained from cutting diameter of 45 cm. The head was equipped with the younger stand (ca. 45% of logs within the specified range). only two movable knives to keep the head relatively short Better results were obtained when the CTL 40HW harvester head (1270 mm), in order to move with ease on the sweep along was used for birch and aspen. The log length accuracy of birch the tree trunk [56, 58]. Another invention resulted from the and aspen showed that more than 80% of the thicker birch and cooperation of scientists from the Technische Universität aspen logs (from the bottom part of the trunk) met the target Dresden (Germany), entrepreneurs from the business sector length (2.50 ± 0.05 m), while only 70% and 50% of the thinner and researchers from the Poznań University of Life Sciences birch and aspen logs, mainly from top parts, reached the target (Poland); a new idea for a harvester head was submitted in [56]. 2016 and the patent was granted in October 2021: Harvester •• An interesting study was carried out by Karaszewski et al. head for hardwood [61 ]. [54, 55] in which log quality was defined as the extent of damage from feed rollers in the outer layer of round wood. South‑West Europe This kind of damage can be especially dangerous for pine wood harvested in summer, as blue-stain can develop and In South-West (SW) Europe, about 36% of the land area reduce timber quality. In broadleaved species, it is unwanted is forested (31.466 mln ha) [23], with a dominance of damage, especially in plywood, where outer layers are of the broadleaved stands (61%), followed by coniferous (31%) highest value. Karaszewski et al. [55] reported that damage and mixed stands (8%). This region has the largest share of from feed rollers on birch plywood logs can reach depths of broadleaved stands and the lowest average growing-stock 3 −1 3.9 mm and cause a 4% volume loss. density (60 m ha ) in the European context, with the low- 3 −1 3 −1 In 2013–2016, a project was completed for the State For- est values in Portugal (52 m ha ) and Spain (60 m h ) 1 3 ests in Poland, with the aim of selecting the most suitable varying considerably from the growing stock of 149 m 1 2 Potential of harvester use for broadleaved tree species (Możliwości ForstInno: Development of an ecologically compatible, highly pro- zastosowania harwesterów do pozyskiwania drewna gatunków ductive method of timber harvesting for Central European forestry th liściastych) – E0-2717-22/13; 2016; supported by the General Direc- – COOP-CT-2005-512681; supported by EC in 6 Framework Pro- torate of the State Forests, Poland, 2013–2016. gramme, 2005–2007. 1 3 Current Forestry Reports (2022) 8:1–19 9 −1 ha in Italy. On the contrary, there is a trend of an annual In SW Europe, the deployment of harvesters is often not increase in terms of growing stock in this region, at a rate of possible due to difficult terrain [ 66], legislation or limited +2.30% over the period 1990–2020, which is the highest in financial capacity [67]. New winch-assisted technology may Europe and can be partly attributed to the expansion of forest soon provide a technical solution to the terrain limitation; area in this region. Nevertheless, it should be noted that the nevertheless, deep structural changes in the legislative and amount of felling has markedly increased in all European economic environment would be necessary to promote har- regions since 1990 but not in SW Europe. vester adoption and use [68]. On the contrary, excavator- All types of forests can be found in all three above men- based units, whose popularity is low in North and Central tioned countries of SW Europe, ranging from natural wood- Europe, are quite popular in SW Europe, as a result of their land to remarkably large forest plantations. Fast-growing lower investment cost and their higher operational flexibility plantations aimed at timber or wood-pulp production, such [69 ]. Italy is an exemplary case, with three out of every four as those of poplar in the Po valley, have a rotation period harvester and processor heads mounted on adapted, often of around 10 years, whereas other plantations focused on pre-owned, excavators, indicating a low willingness to invest the production of particularly valuable timber (e.g. walnut, in newer machines in an effort to minimise the associated maple, ash and cherry) have considerably longer rotation financial risk [70]. In this section, representative studies on periods [62]. Plantations of eucalyptus in Central-West Por- mechanised harvesting of broadleaved tree species were car- tugal have been identified as one of the most intensively ried out in Italy, Portugal and Spain. managed forested areas in Europe [63]. Large plantations Magagnotti et al. [71] compared two strategies for chip have also been established in Spain following the decision and firewood production at two technological levels of to increase the share of energy from woody biomass to the mechanisation in thinning operations in Italy. Thinning was national energy mix [64]. carried out with two methods: as a whole tree system (WTS) Coppice forests are widely distributed in SW Europe. Dif- in partially mechanised operations and as the short-wood- ferent management strategies are implemented in the region, system (SWS) in CTL technology. In the WTS, trees were including the conversion of coppice forests to high forests, initially felled and gathered in bunches of v fi e to eight pieces which, given that it is a long and expensive activity, is unat- by a 13-tonne excavator equipped with a chainsaw felling tractive to private owners. Clear-cutting is allowed in some head and then extracted with a 75-kW farm tractor equipped cases, but law requires that some stands are left to favour with a log grapple. In the mechanised treatment, felling, pro- seed production and sprout regeneration from old stumps cessing and stacking were performed in one sequence by a [62]. Given the ecosystem services provided by coppice for- harvester, based on a 13-tonne wheeled loader. All manual ests, especially in terms of soil protection from erosion, cop- operations were carried out by chainsaw. The best results pices are gaining in importance, yet their utilisation remains were achieved with mechanised harvesting, which caused problematic. In most cases, a medium level of mechanisa- less stand and soil damage compared with manual harvest- tion is implemented, consisting of motor-manual felling ing. In mechanised WTS and SWS, higher productivities and mechanised extraction. The extent of mechanisation is were achieved than with the motor-manual methods (15.48 −1 −1 −1 highly variable, ranging from limited on steep terrain to fully t PMH vs 9.27 t PMH in WTH and 5.35 t PMH vs 0 0 0 −1 mechanised in productive poplar sites like in the Po valley 0.87 t PMH in SWS). In terms of cost, WTS was practi- −1 −1 [62]. In most cases, clear-cutting is applied to limited areas cally the same (5.8 € t for manual vs 6.1 € t for mecha- −1 in natural forests, as in the case of light-demanding species nised); however, mechanised SWS (22.4 € t ) contributed −1 (larch and pines), in order to meet the ecological require- to a significant cost reduction over manual SWS (34.9 € t ). ments of these species and facilitate the natural regenera- The mechanised thinning of walnut plantations was also tion of the stands. On the contrary, selection and shelter- examined in Italy [72]. The authors tested two low-invest- wood harvesting systems are strongly encouraged. Coppice ment fully mechanised operations for producing chips (T1) harvesting technology has evolved in the last decades [30]. or traditional firewood (T2) from the thinning of walnut In these stands, mechanical felling and processing can be plantations. In the first thinning operations (T1), a 4-tonne applied, and there is a trend of increasingly large machines skid-steer loader equipped with a disc saw felling head was in coppice operations, as is occurring in high forests and used to fell alder trees and accumulate them in bunches of plantation operations [65]. However, lighter and less special- five to eight pieces, which were later extracted by a farm ised machinery than that used in high forests has been used tractor with a log grapple. In the second treatment (T2), a so far in coppice forests. Thus, relatively cheap and versatile 95-kW farm tractor equipped with a hydraulic loader and a general-purpose machines (excavators, light forwarders and small-scale stroke harvester was used to fell and process the farm tractors) continue to make up the largest part of coppice trees. The same machine was later converted into a forward- machine fleets, compared with heavier and more expensive ing unit by replacing the harvester with a log grapple and forest machinery [30]. attaching a forestry trailer to the tractor. The equipment used 1 3 10 Current Forestry Reports (2022) 8:1–19 −1 −1 in T1 was less costly than in T2 (54.0 € h vs 88.5 € h ) mechanised whole tree system (WTS), which included chip- −1 and offered a higher felling productivity of 11.74 t PMH ping at the landing; 2) a fully mechanised CTL harvesting −1 compared with 2.40 t PMH . Furthermore, mechanised system for firewood; and 3) a semi-mechanised CTL sys- firewood harvesting, as examined in T2, was financially less tem with manual felling and bunching. The biomass removal effective than traditional motor-manual operations. Given rate from heavy thinning ranged from 34.7 to 44.1 oven dry −1 the price levels during the data collection period, small- tonnes (odt) ha for WTS, much higher than the range of −1 scale mechanised chipping was more profitable than motor- 11.6–30.0 odt ha obtained in CTL trials, a result that may manual firewood production along the full tree size range. be partially attributed to the larger average DBH in WTS. Chipping achieved a financial profit, even with smaller trees The WTS reached maximum productivity rates of 3.9 odt −1 than used in firewood production, suggesting that early thin- PMH for the felling and bunching operation and 6.9 odt −1 ning operations can be economically viable when they are PMH for the forwarding operation. The mechanised CTL carried out in a timely manner before the nurse trees overtop harvesting method achieved a lower productivity range of −1 the crop trees. 0.5–1.3 odt PMH for the harvesting operation. Motor- A harwarder is a combined machine used for timber cut- manual felling and cross-cutting in the CTL system resulted −1 ting, processing and forwarding. A small and a large har- in a productivity range of 0.7–1.9 odt PMH . Manual −1 warder (SH and LH) were tested during thinning in hard- bunching results ranged from 0.8 to 1.0 odt PMH . The wood plantations established on agricultural land in Italy semi-mechanised CTL performed best in terms of firewood −1 [73]. Two treatments were carried out: whole tree sections unit cost, at 62.0 € odt for trees with a DBH of 10 cm −1 (WT) or integrated harvesting (IH) – firewood logs joined compared with 85.2 € odt for the fully mechanised CTL with tree tops. The thinning resulted in a yield of 45 t system. The chip production cost at the landing with the −1 of fresh biomass per hectare. The average gross produc- WTS (average DBH = 10 cm) was 65.3 € odt . tivities of the SH and the LH during the WT harvesting Poplar tree plantations are often established in sites with −1 treatment were 3.46 and 2.77 t PMH , respectively. The moist soil. Forest machine operation performance has been SH was more efficient at felling and loading, while the recognised as being dependent on soil moisture. Tavankar LH was more efficient in the terrain transport work. The et al. [75] studied the effects of soil moisture content on productivity of both machines was about 15% lower in productivity, cost and emissions of greenhouse gases (GHG) the IH treatment. The harvesting cost ranged between 18 resulting from different harvesting systems (chainsaw-skid - −1 and 34 € t , with the LH having a higher operational cost der and harvester-forwarder) in two poplar plantations in than the SH. With both machine types, the harvesting cost Italy and one in Iran. Both harvesting systems performed decreased as the stem size of the harvested trees increased. better in dry than in moist sites, with a higher productiv- Suchomel et al. [74] studied the efficiency of four dif- ity by 20–30%. In Italy, poplar plantations are an important ferent harvesters used in Italy for delimbing and bucking source of high-quality veneer logs. Although the conditions of chestnut trees from coppice stands. The machines were favour mechanised operations, the plantation owners indicate as follows: an Arbro 400S on a JCB 8052 excavator, a that mechanised log-making may result in value losses, due Foresteri RH 25 on a CAT 312 L excavator (in two sites), to poor length accuracy, log surface damage and improper a Lako 55 Premio on a JCB JS 180 NL excavator and a grading. Spinelli et al. [12] studied the performance of man- Timberjack 1270B dedicated harvester with a John Deere ual and mechanised log-making in 10 commercial opera- 762C head. Trees were processed at the landing in order to tions, in terms of occurrence and severity of possible value minimise the impact of machine movement on productiv- losses due to product degradation. Mechanised processing ity. The processors reached high productivity values rang- performed better with regard to length measurement errors, 3 −1 ing from 5.4 to 19.8 m PMH . Furthermore, the influ- while the frequency and severity of log surface damage were ence of tree form was estimated in the Arbro 400S study. the same for both treatments. The size of the branches and the shape of the stem had a In a study by Magagnotti et al. [69 ], the annual use, significant effect on machine productivity, which could annual harvesting, productivity and fuel consumption of 3 −1 3 reach 2.3 m PMH for stems with a volume of 0.2 m . three purpose-built harvesters were compared with those of The study showed that mechanical processors can be suc- three excavator-based harvesters and processors after moni- cessfully deployed for handling whole chestnut trees from toring for 1 year. All machines were owned and operated coppice stands, and that working at the landing and in by private contractors and were representative of the Ital- coppice clear-cuts can improve the operational efficiency ian machine fleet. Despite the challenging mountain terrain, considerably. annual use ranged from 675 to 1525 h per year, and annual Three harvesting systems were examined in a total of harvesting volume from 3,200 to 27,400 m per year. Pro- 11 sites in Q. pyrenaica Willd. coppice stands in Spain ductivity was lower for excavator-based units (5.9 to 17.4 3 −1 [64]. The harvesting systems included the following: 1) a m PMH ) than for purpose-built harvesters (12.7 to 21.8 1 3 Current Forestry Reports (2022) 8:1–19 11 3 −1 m PMH ). Purpose-built machines offered higher annual structure of processed timber and between planned and com- use (69–83% vs 48–69%), and reduced fuel consumption pleted production revenues [81]. These differences mean −1 −1 (8.4–15.3 l PMH vs 13.1–17.9 l PMH ) compared with that silvicultural operations are often carried out at the cost- 0 0 •• excavator-based machines. effectiveness limit [18 ]. Timber extraction is mechanised: Ferrari et al. [76] tried to determine the attitudes of North in all countries the number of skidders is higher than the Italian logging contractors towards mechanised CTL tech- number of forwarders, while felling and processing of timber nology, and to evaluate the potential of machine simulators are mainly motor-manual [82, 83, 84]. when introducing mechanised harvesting for prospective In SE Europe, secondary traffic infrastructure is divided users. In this context, a total of 74 valid interviews were into skid roads, i.e. constructed trails, on sloped terrain and carried out on study participants who had previously tested skid roads in lowland forests. The distance between skid a forwarder simulator. The respondents were aware of the roads usually corresponds to the skidder’s winch rope length mechanised CTL technology potential, both in terms of and usually varies due to difficult terrain conditions, mainly productivity and safety. Respondents employed in firewood slope cong fi uration and river networks. It is generally agreed −1 production were keener on the use of CTL technology. The that 200 m ha is a dense road network on steep terrain main obstacles to the expansion of mechanised CTL tech- in forests (managed in selection cutting) of European fir nology in Italy at the time of the study were financial rather (Abies alba Mill.), Norway spruce and European beech [85, than technical. Thus, simplified low-cost machines specially 86]. In lowland (even-aged) forests (in parts of Croatia and designed for firewood production would be very attrac- Serbia) where forwarders are in use, the distance between tive to Italian firewood contractors. As modern machinery strip roads is usually 20–25 m. Machines are required to stay makes use of computer technology, younger contractors are solely on the strip road network, minimising soil and stand expected to be more interested in them. The promotion of disturbance. mechanised harvesting can be enhanced by the use of simu- Motor-manual cutting dominates in SE Europe, mainly lators; however, new approaches that would maximise their due to the diverse terrain and stand conditions and often benefit and compensate for their large cost must be deployed. due to the ownership structure affecting the introduction and use of CTL technology [87]. The large share of natural South‑East Europe forests rich in broadleaved species with a large DBH, selec- tion cutting and costs of motor-manual harvesting also limit In South-East (SE) Europe, 32% of the land area is forested wider use of CTL technology [88]. At the beginning of the (40.887 mln ha). The average growing stock in this area is twenty-first century, some SE European countries had an 3 −1 116 m ha , and in the last 30 years, the growing stock has integral and controlled introduction of fully mechanised fell- increased by 1.74% (Table 1, [23]). In SE Europe, 78% of the ing in cooperation with all the essential forestry stakehold- forested area is under natural regeneration and expansion, ers [89, 90]. There were also previous applications of CTL while some countries such as Croatia and Slovenia reported technology in the 1990s, primarily associated with salvage a share of >80%. High forest is a common management sys- felling in storm-damaged forests [91] or in clear-cuts of pine tem, and in most forest stands, beech accounts for one-third (Pinus sp.) and Douglas fir (Pseudotsuga menziesii (Mirb.) or slightly more of the entire growing stock. Bončina and Franco) [92]. At that point, some authors have reported that Čavlović [77] state that presence of beech indicates close- harvesters could be successfully applied in thinning and to-nature management in Croatia, especially when compared clear-cutting operations in coniferous cultures and planta- with countries where beech dominates other potential for- tions of fast-growing deciduous species, as well as in pure est vegetation. Most SE European countries, i.e. Slovenia, alder (Alnus sp.) and ash (Fraxinus sp.) stands, just as effec- Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, tively as in spruce (Picea sp.) stands. In other even-aged Albania and partially Croatia, manage beech forests by deciduous forests (e.g. oak and beech), the boundary fac- group selection and/or selection systems, which has pre- tors of application are the dimensions of trees (DBH and served their natural form to a large extent [78]. While in stump dimensions), branching, type and intensity of felling Central and North Europe coppice forests comprise just a and terrain conditions [89]. The authors highlighted that the small share of the total forest area, this forest type covers a use of harvesters is questionable in selection cutting, due to large part of the forest area in some countries of SE Europe, the management type and felling dimensions of the trees. such as North Macedonia 59%, Serbia 65% and Greece 65% Krpan and Poršinsky [89] concluded that the goals of fully [79, 80]. mechanised felling are the following: raising productivity, Climatic extremes have caused major problems with sus- lowering production costs, improving ergonomic aspects and tainable forest management that affect the quality of forest avoiding a labour crisis in forest operations. Today, 20–30 products (i.e. roundwood) in SE Europe, which has resulted years later, fully mechanised felling has become a regular in differences between the planned and produced assortment feature in limited areas of SE Europe. 1 3 12 Current Forestry Reports (2022) 8:1–19 Forest operations carried out with modern technolo- deciduous forests. As a result, in Slovenia, [87] reasearch gies are increasing in SE Europe, the experience gained was carried out leading to the evaluation of standard time- by forestry companies and the forestry profession is grow- tables for the most frequent commercial use of harvesters ing, machines and technology solutions on the market are in thinning operations of coniferous and broadleaved trees. very diverse [91]. However, the number of published papers The authors reported that, in the case of broadleaved forked and completed studies regarding mechanised harvesting in trees, there were frequent difficulties with tree processing— broadleaved stands in SE Europe is still relatively small, and the feeding rollers and cutting knives of the harvester head the experiences presented below come from Croatia, Serbia did not develop sufficient force for the successful cutting of and Slovenia. branches. Harvesters were only three times more efficient Shortly after the first introduction of harvesters in 2001 in than motor-manual cutting. In another study in Slovenia in coniferous stands in Croatia, it was reported that CTL tech- which the share of harvester use against motor-manual har- nology could be effectively used in soft broadleaved stands vesting was considered, it was discovered that in salvage i.e. willow (Salix sp.) and alder (Alnus sp.) [93]. The study, logging harvester use was more frequent than in standard, which used a Timberjack 1270B harvester, was carried out planned harvesting, where more or less half of the timber in a 23-year-old willow stand with a mean felling tree DBH volume was cut with harvesters [96]. of 25 cm and a volume of 0.5 m . Machine productivity In Serbia, according to personal communication with 3 −1 was 17.5 m PMH , and clear-cutting, higher felling den- Stojnić (2021), harvesters are used mainly for pine and pop- sity and larger tree dimensions had a positive impact on lar stands. Earlier studies from Serbia, [11] demonstrated the machine productivity. In contrast, large crowns, preparation effect of forks on the productivity of a John Deere 1470D of the site for harvester operation (removal of a thick layer ECO III harvester in poplar plantations. The average maxi- 3 −1 of shrubs) and an inexperienced (in broadleaved stands) mum productivity ranged from 30.3 to 34.7 m PMH , harvester operator were detrimental, and minimisation of depending on the working method. Harvester productiv- these factors would enhance harvester productivity to 27.5 ity was significantly affected by stem dimensions, within 3 −1 m PMH . In the same year, [94] researched mechanised an average DBH of 40.4 cm and an average net volume of 3 −1 felling in 80-year-old thinned stands of sessile oak (Quercus assortments per stem of 1.55 m stem . petraea (Matt.) Liebl.), European beech and European horn- The first applications of fully mechanised systems in SE beam with the same harvester in Croatia. The researched Europe date back to the 1990s to demonstrations from for- stands had more or less similar stand features: growing stock eign contractors and were associated primarily with salvage 3 −1 3 −1 310 m ha and harvesting intensity 30 m ha . Trees too cutting in storm-damaged forests [91] or conifer monocul- thick for the harvester head were cut by a chainsaw operator, tures [89]. Since 2000, fully mechanised cutting has been as were trees with large crowns. In the felling time structure, used increasingly by contractors (mainly in Slovenia and the harvester share was 81% and 19% of the remaining time Croatia), mostly by private forest enterprises. Krč [91] was used for chainsaw operation. The authors concluded that reported that in the Slovenian Forestry Service, companies the average productivity of felling and processing achieved and research institutions held many workshops to promote by the joint operation of a harvester and chainsaw was 14.5 mechanised cutting. The author concluded that Slovenian 3 −1 m PMH . entrepreneurs prefer investing in more universal machines, According to personal communication with Poršinsky due to the greater chance of effective amortisation. Beguš (2021), the number of harvesters working in Croatia today and Krč [90] stated that the introduction of mechanised cut- is >40. If used in hardwood stands, they are usually involved ting in Slovenia was planned and its course was directed in late thinning and preparatory felling operations (mostly in an effective way by workshops held from 2002 to 2018 with European hornbeam), often in combined mechanised [96]. Slovenia was involved in the Quality Forest project and motor-manual cutting, due to the larger butt swelling of (2017–2019), which addressed the challenge of elaborat- trees with a larger DBH, large crowns and thick branches. ing new professional qualifications, focusing mainly on the Vusić et al. [95] also researched mechanised timber harvest- European Chainsaw Certificate, but also on carrying out tree ing in Croatia by a Timberjack 1470D harvester in 80-year- felling and processing with harvesters. According to Marčeta old European hornbeam and European beech harvesting et al. [97], the use of a chainsaw and skidder is the most sites, and concluded that European beech trees with a DBH common harvesting system in Bosnia and Herzegovina. The >52 cm (considering butt swelling) had to be felled and authors promoted the planning of harvesting operations and processed motor-manually. investments with new CTL technologies and improved work- An increase in the use of fully mechanised felling in both ing methods using GIS and the Analytic Hierarchy Process coniferous and deciduous stands was observed in the past (AHP) method. They proposed that using the AHP method, decade in Slovenia [91]. An expansion of harvester use in integrated with GIS software, would lead to improvement deciduous stands in 2009 was due to harvesting in younger in the planning of forest operations, introduction of modern 1 3 Current Forestry Reports (2022) 8:1–19 13 technologies to replace traditional forestry practice and ulti- Europe than in the other regions. In the analysed latest pub- mately selection of the optimal harvesting system. lished research, investigations into whether applications of Previous research on conifers in SW Europe already dem- multi-tree harvesting lead to higher productivity are com- onstrated how tree characteristics, such as forks, can nega- mon. At the same time, there are published findings on the tively affect productivity, by up to 70% for trees of 10 cm difficulties of harvesting broadleaved species with sweep. DBH and by up to 50% for trees of 40 cm DBH [87, 88]. Slo- Also, it is reported that keeping stable log length is chal- venian experiences shown that large, developed crowns have lenging. It can be concluded that broadleaved trees in North a negative influence on productivity, because the harvester’s Europe are characterised by rather thin branching and lim- head is not able to develop a sufficiently high velocity for ited stem sweep in comparison with trees in Central Europe. effective delimbing [89]. Further Slovenian research [98] Another argument for the influence of these morphological indicated that time consumption per unit product should be tree characteristics is that even though CTL technology has determined to compare the economic efficiency of different been developed for large-scale use in North Europe, there is technologies, and that the direct relationship between prod- no evidence of scientific findings leading to improved effi- uct output and time input is productivity. When comparing ciency of broadleaved species harvesting with CTL methods. the productivity of fully mechanised harvesting systems in CTL technology application seems to remain a major chal- coniferous and broadleaved stands, other influencing factors lenge for Central European countries. should be taken into account, such as stem form (multi-stem, Central-West Europe is characterised by the second single-stem), forking, crown size, share of thick branches, largest average growing stock of all European regions, butt swelling and stem sweep, all of which negatively with a large (44.9%) share of broadleaves. In this region, affect productivity. In a recent study, it was observed that a there is an increasing interest and demand in all countries mixed stand (60/40 coniferous to broadleaved) significantly for mechanised hardwood logging, which is leading to affected the reduction of harvesting productivity, highlight- the development of new technologies. However, most of •• ing the importance of operator experience [99 ]. them are produced individually by small manufacturers. The main factor driving increases in the share of broad- leaved stands is climate change and its associated impacts Conclusions i.e. shifts in species, increasing safety risks and economic effects. From a technical point of view, it is necessary to Findings from the latest research on harvester applications in further adapt the harvester head to handle large crowns broadleaf-dominated stands indicate that there are different of hardwood species, especially those with forks and challenging factors in different European regions (Table  2). thick branches. Ribbed knives for harvester heads were In North Europe, difficulties with harvester use for broad- tested, which lead to higher productivity. At the same time, leaved species were observed in the multi-tree harvesting machines should not become too large, since there is a of trees with sweep; other difficulties were in accuracy of trend towards using small and flexible machines, mainly log length, while in Central (West and East) and South-East for soil protection reasons. Given the current developments Europe, harvester use for broadleaved species has more and the increasing pressure to provide hardwood timber in potential limitations. The development of harvester heads an economically efficient, safe and environmental-friendly dedicated to broadleaved species is mainly focused on Cen- manner, it can be expected that the development will con- tral Europe, where the share of broadleaved species and tinue to progress. their particular morphological features (thick branches and Central-East Europe is characterised by the largest sweep) are a major challenge for CTL technology. There growing stock of all European regions, with a very large have been research projects completed on this topic: in the (47.4%) share of broadleaves. Wider harvester use occurs last 15 years, there were a few larger initiatives leading to the mainly in two countries, Poland and the Czech Repub- design and development of harvester heads for broadleaved lic, where up to ca. 40% of timber is harvested by CTL species, with participation from institutions and universities technology. There are recognised causes of limitations to in France, Germany and Poland. There are currently no initi- wider harvester use, i.e. mountainous areas and broad- atives, but the formation of new ones is highly recommended leaved species, due to their morphological features (mainly because we currently manage and develop forests in a way sweep and thick branches), that lead to lower quality of that is different from how it was done in the last century. delimbing, lower length accuracy, or large tree tops left North Europe is the region with the highest forest cover, unprocessed. For this reason, it is recognised that harvester but with the smallest share of broadleaves. The growing heads require adjustments in design and construction to stock is average in comparison with other regions. A large make timber processing more effective. It is also recog- share of coniferous species is advantageous for wide use of nised that e.g. birch in CE Europe has different features to CTL technology, and this method is more popular in North birch in Scandinavia or other parts of North Europe. Birch 1 3 14 Current Forestry Reports (2022) 8:1–19 1 3 Table 2 Conclusion highlights for each European region North Europe Central-West Europe Central-East Europe South-West Europe South-East Europe The most forested area in Europe, An increase in broadleaf-dominated The largest growing stock of all A large share of broadleaved species The largest share of broadleaved spe- with the smallest share of broad- or mixed stands can be expected. European regions. and the lowest growing-stock den- cies as growing stock. leaved species. Low share of CTL technology, due CTL with a maximum share of 40% sity of all European regions. Partially mechanised harvesting Highly mechanised forest opera- to small clear-cuts, but good, in the region. Although the growing stock has systems are dominant. tions. extensive strip road system. Broadleaved species limit harvester increased, the number of felling Characteristics of broadleaved species Studies focused on the effectiveness Harvester productivity is lower than use. operations has decreased since limit the use of harvesters: large of multi-tree harvesting of broad- in coniferous stands. Use of inno- Scientific projects have been 1990. butt swelling, thick branches, forked leaved species. vative ribbed knives in harvester completed leading to selection In many cases forest machinery can trees, large and developed crowns. Log length accuracy of multi-tree head increased productivity. of the best harvesters for broad- be employed, but promotion and Buck-to-quality method is applied, in harvesting needs improvement. Current research focuses on machine leaved species. Initiatives have an increase in growing stock have which the forester uses wood defects No studies on the difficulties of development for the processing of been undertaken for new designs to be introduced first. and dimensions to determine the harvesting broadleaved species. large hardwood crowns (patented). of harvester heads dedicated to Incremental innovation is applied, cutting position of round wood. Many individual developments by broadleaved species (patented). and financial incentives are Harvester productivity is higher in small manufacturers. Harvester productivity tends to be deemed necessary to boost forest coniferous stands. An increase in supply and demand is lower in broadleaved stands in mechanisation. Expected growth in the number of expected. comparison with coniferous stands. qualified and experienced harvester In contrast, higher productivity can operators for broadleaved stands. be achieved when larger tree tops are left without processing. Limited harvester use for hard- woods, difficulties with: process- ing in top tree parts, delimbing and log length accuracy. Further improvements of harvester heads are expected. Current Forestry Reports (2022) 8:1–19 15 in CE Europe frequently has sweep and thicker branches, in broadleaved stands is the economically important buck- which make it more difficult to process. Therefore, sci - to-quality method, in which foresters define timber assort- entific projects were carried out in last two decades in ments and select the most valuable ones. Similar to in other which selection of the best harvester heads for broadleaved regions, there is an increasing demand for hardwood; there- species was an objective. Other projects were carried out fore, it can be concluded that in the future, the development (mainly in co-operation with scientists from Central-West will move to fully mechanised harvesting operations. Europe) and focused on the construction of heads with Acknowledgements The authors thank Mr. Julian Muhmenthaler from features making the processing of hardwood easier (e.g. WSL for supporting the French literature review. The authors are grate- the CTL 40 HW head and new patent granted in October ful to Professor Tomislav Poršinsky, PhD from the Faculty of Forestry 2021: Harvester head for hardwood). In general, experi- and Wood Technology, University of Zagreb, and Mrs. Silvija Zec, ences with harvester use for broadleaved species indicate president of the Croatian Chamber of Forestry and Wood Technology Engineers, for sharing information on the current number of harvest- that productivity is lower than in harvester use with coni- ers in Croatia. fers. Higher productivity can be achieved only when large tree tops are left without processing. When using harvest- Funding The publication was co-financed within the framework of ers for plywood, damage of the outer layer was observed, the Polish Ministry of Science and Higher Education’s programme: “Regional Initiative Excellence” in the years 2019–2022, Project No. which can lead to economic loses and a lower quality of 005/RID/2018/19. logs. Harvester use for broadleaved species has become unavoidable, mainly due to significant changes in forest Data availability The authors confirm that the data supporting the find- management leading to mixed or broadleaf-dominated ings of this study are available on request. stands and plantations. Therefore, it is expected that in the future, due to increases in broadleaved species shares in Declarations stands, improvements of harvester heads will be necessary to improve the effectiveness of CTL technology. Conflict of Interest The authors declare no competing interests. The region of South-West Europe represents an inter- Human and Animal Rights and Informed Consent This article does not esting case; despite having quite a large (44.4%) share contain any studies with human or animal subjects performed by any of broadleaves in the European context, the region also of the authors. has the lowest growing-stock density. This fact inevitably affects the profits of forest entrepreneurs who are reluctant Open Access This article is licensed under a Creative Commons Attri- to invest in capital-demanding forest machines. Instead, bution 4.0 International License, which permits use, sharing, adapta- local innovations are applied in the form of excavators tion, distribution and reproduction in any medium or format, as long equipped with harvester heads. However, their future as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes deployment will depend on their fuel efficiency, where were made. The images or other third party material in this article are they are outperformed by more expensive, purpose-built included in the article's Creative Commons licence, unless indicated harvesters. In SW Europe, past research on mechanised otherwise in a credit line to the material. If material is not included in harvesting of broadleaved species has largely focused on the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will coppice forests, agroforestry systems and firewood produc- need to obtain permission directly from the copyright holder. To view a tion. More research on mechanised harvesting is needed, copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . as well as policy tools to promote and ease investments in CTL technology. In the face of climate change and the declining forest workforce, mechanised harvesting of References broadleaved stands seems to be the missing link between more intensive and efficient forest utilisation. Papers of particular interest, published recently, have South-East Europe is characterised by the largest share of been highlighted as: broadleaved species in growing stock, and it has the greatest • Of importance (+1.74%) increase of annual growing stock. Even though the •• Of major importance share of fully mechanised forest operations in this region is increasing, partially mechanised harvesting systems still pre- 1. Martin P, Lapeyre D, Douchet O, Restoy G, Guegand G. Récolte mécanisée des taillis en bois ronds (Mechanised harvesting of vail. 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The study confirmed the conference “Šumsko inženjerstvo Jugoistočne Evrope – stanje i intensification of mental demand, effort and frustration izazovi”, 28–30 October 2015. Goč, Srbija. In: https://www .slide experienced by the operators when changing from the pure share. net/ Dusan Stojn ic/ mareta- et- al- istra ivanje- razli itih- tehno conifer stand to the mixed stand. Additionally, work in the logija-sjee-u- za vrnim- sjeama- u- plant aama- e tinar a (accessed on mixed stand resulted in productivity loss, estimated between 25.03.2021). 40 and 57%. Interesting, such an increase in the mental work- 93. Krpan AP, Poršinsky T. Efficiency of mechanical felling and load was independent of the age and experience of the opera- processing in soft and hardwood broadleaved stands – Part 2: tors. Since it is expected that harvesters will be used more Efficiency of harvesters in the culture of soft broadleaf trees. and more in broadleaved stands, results of this study could Šumarski List. 2004;128(5–6):233–44. be used to show a more holistic approach of close-to-nature 94. Krpan AP, Poršinsky T, Stankić I. Efficiency of mechanical fell- forestry and its future implications for harvester operators.) ing and processing in soft and hardwood broadleaved stands; Part 3: Efficiency of harvester in natural thinning stands of hardwood Publisher's Note Springer Nature remains neutral with regard to broadleaf species. Šumarski List. 2004;128(9–10):495–508. jurisdictional claims in published maps and institutional affiliations. 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Forestry Reports Springer Journals

Mechanised Harvesting of Broadleaved Tree Species in Europe

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Abstract

Purpose of the Review The application of cut-to-length (CTL) technology for harvesting and processing timber from broad- leaved tree species is a challenging process, due to thick branches, stem sweep, forks and high wood density. The objective of this review was to describe the current state of harvester use and characterise the effectiveness of mechanised forest operations for broadleaved and mixed forest stands in Europe, paying particular attention to productivity and product quality aspects. An additional aim was to identify the greatest difficulties associated with harvesting broadleaved tree species today and to indicate future challenges and areas for improvement. Recent Findings An interest in wider harvester use for broadleaved tree species started after the storm Lothar in France in 1999. Early experiences demonstrated that lower productivity is common when harvesting broadleaved tree species, due to limitations in delimbing and the high frequency of sweep. Initially, modifications were made to harvester heads, while a newly designed head (CTL 40 HW) was later developed within a European project in 2005–2007. Using various heads, very high productivity was achieved in some cases, but log recovery was unsatisfactory, with large tree tops left without delimbing. The delimbing was of lower quality and log length inaccuracy was observed, as well as economic losses due to damage to plywood caused by feed rollers. These issues resulted in a change in harvester head construction, including work on a patent for a head designed specifically for harvesting broadleaved tree species. Summary The harvester heads that have been developed to date for broadleaved tree species have mainly been used within Central Europe, where the high incidence of broadleaved tree species and their particular morphological features (thick branches and sweep) are a major challenge for CTL technology. There have been many research projects related to this issue: in the last 15 years, there were a few larger initiatives leading to the design and development of harvester heads for broad- leaved tree species, with participation from institutions and universities in France, Germany and Poland. There are currently no ongoing initiatives, but the formation of new ones is strongly recommended because today’s forests have a growing share of broadleaved tree species and are being managed to an increasing extent with CTL technology. Keywords Deciduous tree species · Forest operation · Hardwood · Harvester · Harvester head · Productivity · Thick branch This article is part of the Topical Collection on Forest Engineering * Piotr S. Mederski Department of Forest Utilisation, Faculty of Forestry piotr.mederski@up.poznan.pl and Wood Technology, Poznań University of Life Sciences (PULS), ul. Wojska Polskiego 71A, 60-625 Poznań, Poland * Janine Schweier janine.schweier@wsl.ch Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Andreja Đuka Switzerland andreja.duka@sumfak.unizg.hr Department of Forest Engineering, Faculty of Forestry Petros Tsioras and Wood Technology, University of Zagreb, Svetošimunska ptsioras@for.auth.gr 25, 10002 Zagreb, Croatia Leo G. Bont Department of Harvesting and Technology Forest leo.bont@wsl.ch Products, Lab of Forest Utilisation, Aristotle University Mariusz Bembenek of Thessaloniki, P.O. Box 227, 54-124 Thessaloniki, Greece mariusz.bembenek@up.poznan.pl Vol.:(0123456789) 1 3 2 Current Forestry Reports (2022) 8:1–19 harvesting has become more popular in Europe [15]. In Introduction general, forest operations carried out by harvesters differ among countries in Europe, with a larger share of CTL In contrast to harvester use for forest operations in conifer technology in North, Central and West Europe in com- stands, the use of harvesters in broadleaved forest stands •• parison to South and South-East Europe [15, 16, 17, 18 ]. has a relatively short history. This is because harvesting One reason for this variation is the tree species composi- and processing timber from broadleaved species is more tion–coniferous tree species are more suitable for CTL difficult than from coniferous tree species e.g. spruce and technology and more dominant in North, Central and West pine. Thick branches make it difficult to obtain logs from Europe [15, 19]. However, Scots pine (Pinus sylvestris L.) the top parts of trees, and hardwood trees have higher and Norway spruce (Picea abies (L.) Karst) are conifers wood density than conifers. that are recognised as vulnerable to changing climate con- Besides challenges associated with certain tree spe- ditions, and their abundance in Central European lowland cies, there may be other factors that limit wide harvester forests is expected to decrease significantly with global use, like the low rate of investment capability and fear of change [20]. At the same time, broadleaved tree species unemployment. However, today’s market conditions, with may find the new conditions more suitable; according to low availability of manpower, may accelerate wider use of the latest findings and predictions, European beech and cutting-edge harvesting technology. pedunculate oak (Quercus robur L.) will become (increas- One of the first records of harvester productivity in broad - ingly) dominant in large parts of Central Europe [20]. leaved forest stands was with the harvester type Sifor 614 in Thus, an increasing potential for the use of CTL technol- France in 1993–1996 [1, 2], where European beech (Fagus ogy can be expected, taking into account that the interest sylvatica L.), oak (Quercus sp.), European hornbeam (Carpi- in manual work has declined recently. nus betulus L.), chestnut (Castanea sativa Mill.), birch (Bet- There is a strong need to adapt silvicultural management ula sp.) and aspen (Populus sp.) were harvested. Early use of practices and to provide forest managers with evidence- harvesters was also recorded in the 1990s, in Finland (birch) based recommendations, especially regarding CTL technol- and in Spain (Eucalyptus sp.) [3, 4, 5]. Basically, the use of •• •• ogy [21 , 22 ]. Based on initial studies of the available harvesters for broadleaved species was rather sporadic at literature, it was hypothesised that development of CTL the end of the twentieth century. This changed after wind technology for broadleaved species is an unavoidable step damage resulting from the storm Lothar in 1999, when large in the expansion of forest operations. Therefore, the objec- areas needed clearing and harvesters were a suitable option tive of this study was to assess the current state of harvester in comparison to low-safety motor-manual salvage removal use and characterise the effectiveness of its use for broad- [6]. The need for wider harvester use led to head modifica- leaved tree species in Europe, paying particular attention tions to make timber processing more effective and with to economic (productivity) and product quality aspects. An satisfactory productivity [2]. additional objective was to identify challenges with mecha- Bigot and Cuchet [7] conducted a large study of har- nised forest operations in broadleaved or mixed stands and vester head usability in broadleaved forest stands in France to establish what could or should be improved to enhance and tested 40 harvesters with heads originally dedicated to the efficiency of the timber harvesting of deciduous trees. coniferous species and some adapted for broadleaved tree species. Compared to use with coniferous species, lower productivity was observed and more frequent repairs were Material and Methods needed with broadleaved tree species, which is still true today. In 2004–2005, studies were carried out on harvester An English literature review was conducted in the databases use in coppice chestnut forest stands, and later research Web of Science, Scopus and Google Scholar in April and considered beech and eucalyptus forest stands in Europe May 2021. The following keywords were used to retrieve and North America [8, 9, 10]. Further studies focused on available studies: hardwood cut-to-length; mechanised harvester use in poplar short-rotation plantations [11, 12], harvesting of broadleaves; mechanised harvesting of hard- as well as on improved productivity during multi-stem wood species; mechanised forest operations in mixed stands; processing of spruce and birch [13]. Lower quality wood mechanised forest operations in broadleaved stands; mecha- produced during delimbing, as well as bark shavings, were nised thinning operations in mixed stands; mechanised thin- recognised as useful energy sources. Recently, studies ning operations in broadleaved stands; harvester thinning have indicated that trees with thinner branches in younger operation. stands could be processed efficiently with harvesters [14]. In the first step, no specific time span was chosen in order Meanwhile, cut-to-length (CTL) technology (defined to get a comprehensive basis of relevant studies for the intro- here as harvester use for processing short logs) for timber duction and discussion parts of the article. Titles, abstracts 1 3 Current Forestry Reports (2022) 8:1–19 3 and/or keyword fields were read to decide whether each study conifers in Europe (67%) and the lowest share of broadleaved was related to the topic. In total, 227 studies were identie fi d tree species (16%), with both forest types usually managed using Web of Science, another 327 with Scopus and 229 with as high forests. Broadleaved tree species, especially of the Google Scholar. After excluding studies that were out of scope, younger age classes, are most often used for energy pur- older than 10 years (published before 2011) or double-counted, poses [24, 25]. The average growing-stock density is 129 m −1 a total of 51 studies were considered further to review and ha and is stable: in the last 10 years (2010–2020), it has summarise the current state of CTL harvesting in hardwood increased by 0.8% [23]. stands. CTL technology is widely used in North Europe  [15, •• In a second step, national sources were searched, including 18 ], where strip roads are usually established every 20 m sources in local languages. These included not only magazines to make stands accessible for harvesters. However, a larger dedicated to practitioners, but also websites (e.g. www.w aldw share of mechanised harvesting is present in Sweden and issen. net, which is maintained in German, French, Italian and Finland than in Baltic countries [15, 17]. In the last decade, English) and personal communication between experts and CTL technology applications in broadleaved forest stands the authors of this study. Specifically, the following magazines were mostly carried out in Finland and Latvia and focused were screened: Forsttechnische Information (Germany), Der on birch and alder. In Lithuania, processing with a newly Waldbauer (Austria), Wald & Holz (Switzerland), Drwal designed harvester head was carried out on birch and aspen (Poland), Šumarski list and Nova mehanizacija šumarstva [26]. (Croatia) and FCBA reports (France). Finally, international Few studies from Finland were carried out in stands with and local research projects, dissertations and reports were downy birch (Betula pubescens Ehrh.). One of these studies searched and considered. Additional sources were also con- was focused on the productivity of multi-stem harvesting in sidered based on the expert knowledge of all co-authors. thinning and clear-cut stands dominated by young downy Results were reported according to their geographical birch trees, from which pulpwood and energy wood sec- assignment, distinguishing regions in Europe as North, Cen- tions were processed. The Komatsu 901.4 harvester with tral-West, Central-East, South-West and South-East, with their a Komatsu 350.1 harvester head was used with an option respective countries (Table 1) [23]. References were structured for multi-stem harvesting [25]. Tree-specific time studies according to the region and based on four important aspects were conducted, and productivity models based on these related to CTL hardwood harvesting: productivity and cost, investigations were elaborated for multi-stem cutting. product quality (timber assortments), delimbing quality and Clear-cutting in older stands resulted in a higher cutting utilisation of tree stems for timber assortments. However, the productivity than in younger stands where thinning was sections might differ slightly depending on the regions’ char - carried out. Multi-tree cutting was more productive, but acteristics and the relative importance of challenging factors only marginally and in both types of stands. This was due studied in the local conditions. to the small share of multi-stem cutting. Harvesting condi- tions were more favourable in clear-cutting than in thinning Results and Discussion operations. The multi-tree harvesting productivity was from 3 −1 5.6 to 17.4 m PMH (productive machine hour without 3 −1 Overview delays) in clear-cut stands and from 4.8 to 10.9 m PMH in thinned stands. In terms of multi-tree cutting, the har- The forest cover and tree species composition of forests in vester head processed only 1.2 trees per cycle in clear-cut Europe vary across the regions (Table 1). The most forested stands and 1.1 trees per cycle in thinning stands. Finally, region is North Europe, which also has the largest share of it was concluded that improving harvesting equipment for coniferous tree species. However, the highest growing-stock multi-tree cutting of birch and other tree species that have density is in Central-East Europe. Broadleaved tree species stems with sweep is necessary. occur in all regions, with South-West Europe having the largest In another study from Finland, downy birch harvesting share of forest stands with deciduous tree species (Table 1). was carried out in young (age 12 to 29 years) forest stands [24]. A Valmet 911.3 harvester was used for cutting with an engine power of 170 kW. The harvester was equipped with Experiences with Harvesting Broadleaved the Bracke C16.b accumulating felling head fitted with a Tree Species circular saw disc. A small volume of trees harvested with clear-cutting methods led to satisfactory productivity, from 3 −1 North Europe 6 to 24 m PMH , in spite of harvesting residues of ca. 7% of the total biomass that were left on the harvesting sites. In North Europe, about 54% of the land area is forested In a final research from Finland, the impact of the remain- (71.299 mln ha), and this region has the largest share of ing young spruce understorey on the cutting productivity in 1 3 4 Current Forestry Reports (2022) 8:1–19 1 3 Table 1 Main characteristics of forest management in the five European regions [23] Selected feature North Europe Central-West Europe Central-East Europe South-West Europe South-East Europe Countries in the region Denmark, Estonia, Finland, Austria, Belgium, France, Belarus, Czech Republic, Andorra, Holy See, Italy, Albania, Bosnia and Herze- Iceland, Latvia, Lithuania, Germany, Ireland, Liech- Georgia, Hungary, Poland, Malta, Monaco, Portugal, govina, Bulgaria,Croatia, Norway, Sweden tenstein, Luxembourg, Neth- Republic of Moldova, Spain Cyprus, Greece, Montenegro, erlands, Switzerland, UK Romania, Slovakia, North Macedonia, Serbia, Ukraine Slovenia, Turkey Forested land area, % 53.8 27.9 27.3 35.5 31.5 Average growing-stock den- 129.0 242.1 254.6 59.7 115.7 3 −1 sity, m ha Growing stock:   broadleaves, % 25.6 44.9 47.4 44.4 53.1   conifers, % 74.4 55.1 52.6 55.6 46.9 Growing stock trend (annual +0.80 +1.06 +1.58 +1.06 +1.74 growth in 1990–2020), % Management system High forest High forest High forest High forest High forest Coppice with standards Coppice with standards Coppice Coppice Distance between strip roads/ 20 20–40 20 or 30 Depends on terrain conditions Depends on terrain conditions skid trails, m Size of clear-cuts, ha The most common is 4–10 Small, 1–2 4–6 Small, 1–3 Small, if feasible Share privately owned f orest Large Large Medium Large Small, apart from Slovenia >75% and Serbia 47% Dominant harvesting sy stem Fully mechanised Partially mechanised Partially mechanised Partially mechanised Partially mechanised All countries in the region; countries with studies considered suitable for this paper are given in bold High forest originating from seeds or planted seedlings, in contrast to coppice forest In Sweden, larger area of clear-cuts can be >20 ha; however, any application for clear cut >0.5 ha has to be approved by Forest Agency Large, medium and small share, understood as >50%, 25–50% and <25% privately owned forests, respectively Fully mechanised and partially mechanised, understood as min. 70% and min. 30%, respectively, of timber being cut with a harvester-forwarder system Current Forestry Reports (2022) 8:1–19 5 thinning stands dominated by downy birch was investigated forest, which can be even-aged management, continuous [27]. Tests were carried out on 50- to 75-year-old birch trees cover forestry or uneven-aged forestry. One exception is with a mean diameter at breast height (DBH) from 14 to France, which has a large share of broadleaved tree species 24 cm. A medium-sized John Deere 1070/745 with a boom (64%) and where around 30% of the total forest area is tra- reach of 10 m was used in the study. Different productivi- ditionally managed as coppice with standards [30]. A large 3 −1 ties were achieved from 13 to 29 m PMH . In particular, share of the forest area in CW Europe is managed using for- 3 −1 productivity was 15–29 m PMH in thinning stands where est strip roads with 20- to 40-m distance between them, and 3 −1 there were no spruce trees present, 14–24 m PMH in with restrictions limiting penetration by any machine in the stands where spruce trees were present but were not consid- zone between the strip roads. Again, France is an exception, 3 −1 ered, and 13–21 m PMH in stands where spruce under- as it doesn’t make use of a defined strip road network [31]. growth was retained. Since clear-cuts are usually tolerated for small areas only In Latvia, grey alder is an important tree species in the in CW Europe (e.g. <1 ha in Germany, <2 ha in Austria), management of non-state forests. Motor-manual felling is a the dominant harvesting system is selective cutting, which is common method in non-state forests, but fully mechanised conducted in a motor-manual system, partially mechanised forest operations are carried out in final felling. Liepiņš system (i.e. motor-manual felling and mechanised process- et al. [28] examined the effectiveness of motor-manual and ing) or fully mechanised system. The choice depends on the mechanised harvesting, in which productivity reached 2.99 strip road density but also on the forest ownership. There 3 −1 and 7.04 m PMH , respectively. In spite of the lower pro- is a large share of privately owned forests (almost 75% in ductivity, motor-manual harvesting was more cost-effective France, approx. 50% in Austria and Germany). Owners are than mechanised forest operations. It was also concluded responsible for small forest areas only and do not make that improvements in work organisation that could lead to large investments. The trend to use light and less special- higher productivity and a potential increase in labour costs ised machines can be observed in coppice forests as well, in the near future may increase the financial competitiveness which is consistent with the rural and small-scale character of mechanised harvesting. of coppice forestry [30]. The majority of fully mechanised It was reported that the average cost for final felling in felling operations are carried out by contractors e.g. approx. Latvia, including cutting, off-road transport and further 90% in Germany [32]. In hardwood stands, the share of fully −3 transportation to the customer, reached 16.54 € m in 2015 mechanised harvesting operations is only about 10–20%. [29]. For these three specific operations, the calculated costs Schuldt [33] assessed the status of partially and fully mech- −3 were similar at 5.70, 4.94 and 5.90 € m , respectively [17]. anised harvesting methods for hardwood stands, thereby −3 In thinning operations, the average cost was 21.60€ m but focusing on a medium DBH of 20–35 cm. He recognised −3 was more differentiated: 9.39, 6.14 and 6.07 € m , respec- that a machine with at least a medium-sized engine power tively [17, 29]. Differences in harvesting costs depended is needed and that it should be run by a skilled operator. mostly on the type of felling (thinning or final felling) but Smaller harvesters were not considered suitable because also on forwarding conditions, such as soil bearing capacity they have a shorter boom reach and thus require a denser and forwarding distance. However, there was no evidence network of strip roads, as confirmed by Mederski et al. [34 ]. that tree species composition had a significant impact on Selected studies included in this paper were from Austria, harvesting costs. France, Germany and Switzerland. A study on product quality was carried out on birch and Labelle et al. [35] conducted a pilot study consisting of aspen in Lithuania and indicated that keeping a stable length 82 sample plots in a 4.5-ha beech-dominated mixed stand in of logs is a challenge for harvesters. Zinkevicius et al. [26] Germany, aiming to assess the influence of silvicultural man- reported that, for birch and aspen logs, the length accuracy agement (selective-cut vs clear-cut) and tree species (spruce of cut logs by a motor-manual operator was better than the vs beech) on the performance of the analysed harvester. The accuracy of bucking by the CTL 40 HW harvester head stand had an average age of 90 years and an estimated vol- 3 −1 designed specifically for broadleaved tree species. ume of 280 m ha . A six-wheeled single-grip harvester was used for the felling operation (2005 TimberPro 620-E Central‑West Europe equipped with a LogMax 7000C harvester head). The result- 3 −1 ing felling productivity for beech trees was 24.7 m PMH 3 −1 3 −1 In Central-West (CW) Europe, about 28% of the land area (23.4 m PMH in selective-cut and 27.5 m PMH in 0 0 is forested (38.966 mln ha) [23]. The average growing-stock clear-cut). This was, however, 31–45% lower than the pro- 3 −1 3 −1 3 −1 density is 242 m ha , whereas Switzerland (354 m ha ), ductivity observed in spruce stands (33.9 m PMH in 3 −1 3 −1 3 −1 Germany (321 m ha ) and Austria (299 m ha ) represent selective-cut and 36.0 m PMH in clear-cut). Processing the upper limit. Overall, the growing stock is increasing in was more time consuming in selective-cut compared with this region. The most common management system is high clear-cut operations, due to larger tree diameters (DBH 41 1 3 6 Current Forestry Reports (2022) 8:1–19 cm vs 32 cm). In another pilot study, [36 ] observed four observed for larger diameters: the productivity increased to 3 −1 3 harvesters (two-wheeled and two-tracked machines) that 14 m PMH at a stem volume of 0.20 m . The multi- worked in four different plots with a high percentage of stem structure did not result in technical problems or a sig- large-diameter trees (oak, European beech). Two operations nificantly greater time consumption for the harvester, even were conducted on a fully mechanised basis and processing though it was slightly more time-consuming to grab and fell was the most time-consuming step, taking 54–65% of the multi-stemmed trees than single-stemmed trees. Compared time per cycle. The harvesting productivity varied between with manual felling, the harvester left significantly (5 cm) 3 −1 29 and 43 m PMH on average. taller tree stumps, although [42] showed that mechanised In France, the mechanised processing of logs from large cutting does not seem to have any negative effects on cop - crowns of broadleaved species is of particular interest. Ruch pice regeneration and growth. et al. [37] compared two harvesting systems, the first with Fully mechanised hardwood harvesting depends mainly a grapple saw that was attached to a forwarder and the sec- on the harvester head or the fuelwood feller unit. Using soft- ond with the grapple saw that was attached to an excavator wood harvester heads in hardwood stands is technically dif- which processes the crowns for a forwarder. The one- and ficult. Nordic products are light and handy, but felling heads two-machine systems were analysed in terms of productiv- have been constructed for tree species with less dense wood ity, efficiency and technical and economic aspects. Nine key [43]. On the other hand, North American felling heads are factors influencing productivity were identified. The authors more robust and powerful but must be mounted on heavy concluded that (i) the grapple saw is an easy-to-use piece machines, which stands in conflict with soil protection issues of equipment which is efficient and requires a comparably and Central European silvicultural practices [44]. Chakroun small investment for the contractor (15,000 €), and (ii) the et al. [44] performed a study in which two recently devel- single-machine system performs best, with costs varying oped fuelwood feller units from French manufacturers were −1 −1 between 8 and 14 € t , compared with 20 to 23 € t for a compared in typical hardwood biomass forests: (a) thinning two-machine system. Several studies (e.g. [38]) have been in regular high forest and (b) clear-cutting in coppices. The conducted in France to observe the current productivity of feller units were tailored for the tree species available in applied hardwood harvesting systems. These studies indi- Central and South Europe, allow multi-tree handling, and cated that there was a significant increase in the produc- were designed to be mounted on medium-sized excavators. tivity of the machines involved in hardwood harvesting in The main findings of the study were that the significant fac - recent years (around +22.7% from the period of 2000–2007 tors influencing productivity were tree size and stand type to 2008–2015) but that the rate of mechanisation of hard- (with productivity generally higher in high forests), with 3 −1 wood cuts remains low (but increased from 10% in 2013 values ranging from 5.7 to 17.1 m PMH . to around 15% in 2018) [39]. The technical complexity of Kleinschmit [45] aimed to determine the economically dealing with the most poorly shaped hardwoods, combined optimal processing intensity of beech crowns in Germany. with the absence of an ideal harvester head, could explain He conducted trials with highly mechanised systems this observation. using a John Deere harvester 1270E IT4 with a Waratah Mechanised harvesting of hardwoods is mainly carried felling head H480C developed for timber of large dimen- out by not only harvesting machines in CW Europe, but also sions. Kleinschmit examined the processing of beech trees by modified excavators equipped with harvester heads [40]. and presented a decision model with the aim not only of As there is no specific harvesting machine dedicated to hard- explaining the economic relationships of crown processing, woods, a lower annual volume was harvested in broadleaved but also of assisting decision makers in determining the 3 −1 −1 stands, i.e. 14,000 m year machine , compared with economically optimal processing intensity or the economi- 3 −1 −1 23,500 m year machine observed in softwood stands cally optimal top diameter and raising their awareness of the in France [40]. cost dependencies in the case of changed economic frame- Even though less important than high forests, traditional work conditions. Branches with a >7 cm over-bark diameter (and partially modern) coppice forests play a role in CW could be identified as cost drivers. These branches require Europe. Machines larger than traditional forestry tractors are additional time consumption of about 24 s just for cutting. increasingly being used for coppice felling and processing Processing logs with branches took five times longer than [30]. Suchomel et al. [41] determined the technical feasi- processing logs with the same length but from tree parts bility and the time consumption of harvesting oak coppice without branches. with an average DBH of 17.5–18.2 cm. They investigated Cacot et  al. [46] performed a study on a new type of an HSM 405H 6WD harvester with a CTL 40HW harvester delimbing tool for hardwood trees in France: oak, chestnut, 3 −1 head and found an overall productivity of 9.5 m PMH birch and aspen. The focus was on the shape of the delimb- for trees with a DBH >10 cm and an average stem volume ing knives modified by the integration of ribs in the cutting of 0.17 m . The main advantage of the studied harvester was area. In a first step, several types of knives were compared 1 3 Current Forestry Reports (2022) 8:1–19 7 in the laboratory in terms of the energy required for cutting. the distribution of the strip road network is irregular and Based on this evaluation, two harvester heads, each equipped depends mainly on the land configuration. with one fixed and two mobile ribbed knives (John Deere The dominant harvesting system in CE Europe is selec- 752 HD, Kesla 25 RH harvester head), were compared with tive cutting, which is used in all premature stands. Clear-cuts the original knives over 1 year. Using the ribbed knives led are usually applied on a maximum area of 4 ha, with the to an increase in productivity by 21% in the delimbing pro- exception of 6 ha in Poland. CTL technology used during cess, although the increase in overall productivity could not thinning and final felling covers 38% of the total harvest- •• be proven statistically. ing in the Czech Republic and 40% in Poland [18 , 49, For several reasons (e.g. work safety, salvage logging, 50], compared with only 5% in Slovakia and 2% in Roma- lack of own personnel), some state forest administrations nia [17]. In CE Europe, CTL technology is used mainly for and federal research institutes within CW Europe actively coniferous species, but harvesters can be used for broad- •• promote fully mechanised hardwood felling. The Austrian leaved species as well, such as birch [51, 52 ], oak [53], •• Research Centre for Forests (BFZ), for instance, published alder [54, 55] and aspen and poplar [56, 57 ]. However, a video [47] in which they state that a major challenge is broadleaved species can be seen as a factor limiting har- the undergrowth and argue that the basic requirement for a vester use in CE Europe, including in mountainous areas successful operation is good visibility of the strip roads, the [15]. Taking into account the distribution of harvesters and future crop trees and the trees selected for removal. the share of broadleaved species in the analysed region, it The potential for future mechanised hardwood harvest- can be concluded that ca. 10–15% of hardwood timber in ing in CW Europe is significant. In recent years, France Poland is obtained by harvesters, while in other countries, seemed to be very active in developing and testing solutions such as the Czech Republic, Slovakia, Romania and Hungry, for mechanised harvesting of hardwood species. This can timber from broadleaved stands is rarely produced with fully be explained mainly by its forest structure. Current trends mechanised technologies. show that companies are reacting to the demands of practi- Studies on the productivity of harvesters when process- tioners. This development is also driven in part by climate ing the timber of broadleaved species have shown that it change [48] and its associated impacts (e.g. dying ash and may differ from values for harvesting coniferous trees in beech trees). In Switzerland, a fully commercial technical CE Europe. In earlier studies carried out by Mederski et al. solution was designed and constructed to safely and effi- [58] in Poland, harvester thinning operations in broadleaved ciently fell hardwoods, including large trees, that might be mixed stands (mainly birch) resulted in a productivity of 3 −1 dry or affected by illness. In this solution, a safety platform 13.40 m PMH . This study was based on a harvester head is mounted on a felling excavator with a 15-m boom using specially designed and built for broadleaved species: CTL a quick-change system. The trees are held by the excavator 40HW. A much higher productivity was achieved when har- grapple during the felling operation and the safety platform vesting 46- and 61-year-old birch with a Sampo Rosenlew then encloses the stem and protects the feller from falling 1066 and Keto 150LD head [51]. In the study, productiv- −1 branches and crown parts. After the feller has left the area ity reached 26.95 and 40.46 PMH in younger and older of danger, the tree is safely moved by the excavator in the stands, respectively, and was higher by 44% and 41%, desired felling direction [personal communication with respectively, in comparison with productivities achieved Weber, 2021]. when harvesting pine of the same age. These differences were mainly due to tree size (birch had a larger volume) and, Central‑East Europe of considerable importance, to the fact that birch logs with a diameter over bark of up to 12.3 and 16.2 cm were processed In Central-East (CE) Europe, 27.3% of the land area is in younger and older stands, respectively. In comparison, covered with forest (44.735 mln ha), with broadleaved and processing of pine was more effective for log diameters of coniferous stands summing to ca. 40% each and mixed up to 9.4 and 10.6 cm over bark in younger and older stands, stands to ca. 20% [23]. CE Europe is the richest area in respectively [51]. 3 −1 terms of growing stock, at 254.6 m ha , with the high- In another study using a large pool of data in Poland 3 −1 3 −1 est values in Romania (339.8 m ha ), the Czech Repub- [59], the mean productivity of 15.77 m PMH when har- 3 −1 3 −1 lic (295.4 m ha ) and Poland (287.9 m ha ) [23]. The vesting broadleaved species was lower than the productiv- majority of areas are managed in the form of high forest as ity achieved in pine stands, which varied from 18.57 m −1 3 even-aged and uneven-aged stands. Coppice forests are rare PMH in younger stands (41–60 years old) to 22.60 m −1 and tend to be grown as coppice with standards. Stands are PMH in older stands (81–100 years old) [19]. In other accessible by machines with networks of strip roads, with studies in Poland, in which a Ponsse harvester was used with 3 −1 a distance between them of 20 m for harvesters and ca. 30 head H7, the productivity of oak was 20.32 m PMH for m for skidders. Exceptions exist in the mountains, where harvested trees with a mean DBH of 20.0 cm and 0.25 m 1 3 8 Current Forestry Reports (2022) 8:1–19 of timber was harvested from one tree on average [53, 60]. harvesters for felling and processing timber of the four most The interesting aspect of this study was the use of tree trunks common and economically important broadleaved species for logs. It was demonstrated that the mean top diameter in the country: oak, beech, birch and alder. All tests were over bark of the last log (from the highest tree part) was carried out in 40- to 80-year-old stands. Harvesters of 11 13.3 cm when attempting to process logs up to the smallest different producers were tested with 11 different heads. Tri - diameter of 7.0 cm over bark. It was also confirmed that the als were carried out on 60 sample plots in North Poland and top diameter of the last log depended on the DBH of the tree the considered parameters of harvester efficiency were the from which that log was obtained. It is a challenge to make following: (1) productivity, (2) cost, (3) range of trunk utili- harvesting small trees profitable. A study on harvester use in sation for logs, (4) length accuracy, (5) quality of delimbing an 8-year-old poplar plantation in Poland showed that pro- and (6) damage to logs. Considering all of these param- 3 −1 ductivity reached 7.5 m SMH (scheduled machine hours, eters, the best results were achieved when a Waratah head with delays) when the multi-tree harvesting mode was used was used, although good results were also obtained with 3 −1 •• and 6.5 m SMH in single-stem processing [57 ]. heads by Ponsse and Valmet. The average productivity was 3 −1 The quality of delimbing was studied extensively by Mederski 15.77 m PMH in all analysed stands, with maximum 3 −1 [51] in a comparison of pine and birch logs. The two tree species productivity reaching 36.16 m PMH in oak stands with were analysed separately in two mixed stands in Poland with a mean DBH of 28 cm. Generally, higher productivity was ages of 46 and 61 years. Testing of the quality of delimbing was achieved in alder stands, where larger trees were harvested. carried out as measurements of stubs left after delimbing with a It was also discovered that tree tops with larger diameters Keto 150LD head. The largest stubs were observed on the birch (in comparison to coniferous species) are typically left, as logs from older trees, with a mean stub length of 34 mm, while a result of difficulty delimbing in tree crowns. Overall, the on the birch logs from the younger stand, the mean stub length completed project popularised harvester use for broadleaved was only 26 mm. On the pine logs, the stubs were significantly species in Poland and convinced forest owners and forest smaller: 13 and 12 mm on logs from older and younger trees, entrepreneurs to consider wider harvester use in broadleaved respectively. Within this study, the accuracy of log length was or mixed stands. also considered, and it turned out that the cross-cutting accuracy The CTL 40HW harvester head, developed in 2005–2007 was highest for the butt ends of the older pine stand (more than within the ForstINNO project, was a new harvester head 60% of the logs had a very narrow length tolerance set in the dedicated to broadleaved species and tested in CE countries. harvester computer: 2.53–2.55 m). The least accurately cut logs The CTL 40HW was designed to cut trees with a maximum within this category were the top pine assortments obtained from cutting diameter of 45 cm. The head was equipped with the younger stand (ca. 45% of logs within the specified range). only two movable knives to keep the head relatively short Better results were obtained when the CTL 40HW harvester head (1270 mm), in order to move with ease on the sweep along was used for birch and aspen. The log length accuracy of birch the tree trunk [56, 58]. Another invention resulted from the and aspen showed that more than 80% of the thicker birch and cooperation of scientists from the Technische Universität aspen logs (from the bottom part of the trunk) met the target Dresden (Germany), entrepreneurs from the business sector length (2.50 ± 0.05 m), while only 70% and 50% of the thinner and researchers from the Poznań University of Life Sciences birch and aspen logs, mainly from top parts, reached the target (Poland); a new idea for a harvester head was submitted in [56]. 2016 and the patent was granted in October 2021: Harvester •• An interesting study was carried out by Karaszewski et al. head for hardwood [61 ]. [54, 55] in which log quality was defined as the extent of damage from feed rollers in the outer layer of round wood. South‑West Europe This kind of damage can be especially dangerous for pine wood harvested in summer, as blue-stain can develop and In South-West (SW) Europe, about 36% of the land area reduce timber quality. In broadleaved species, it is unwanted is forested (31.466 mln ha) [23], with a dominance of damage, especially in plywood, where outer layers are of the broadleaved stands (61%), followed by coniferous (31%) highest value. Karaszewski et al. [55] reported that damage and mixed stands (8%). This region has the largest share of from feed rollers on birch plywood logs can reach depths of broadleaved stands and the lowest average growing-stock 3 −1 3.9 mm and cause a 4% volume loss. density (60 m ha ) in the European context, with the low- 3 −1 3 −1 In 2013–2016, a project was completed for the State For- est values in Portugal (52 m ha ) and Spain (60 m h ) 1 3 ests in Poland, with the aim of selecting the most suitable varying considerably from the growing stock of 149 m 1 2 Potential of harvester use for broadleaved tree species (Możliwości ForstInno: Development of an ecologically compatible, highly pro- zastosowania harwesterów do pozyskiwania drewna gatunków ductive method of timber harvesting for Central European forestry th liściastych) – E0-2717-22/13; 2016; supported by the General Direc- – COOP-CT-2005-512681; supported by EC in 6 Framework Pro- torate of the State Forests, Poland, 2013–2016. gramme, 2005–2007. 1 3 Current Forestry Reports (2022) 8:1–19 9 −1 ha in Italy. On the contrary, there is a trend of an annual In SW Europe, the deployment of harvesters is often not increase in terms of growing stock in this region, at a rate of possible due to difficult terrain [ 66], legislation or limited +2.30% over the period 1990–2020, which is the highest in financial capacity [67]. New winch-assisted technology may Europe and can be partly attributed to the expansion of forest soon provide a technical solution to the terrain limitation; area in this region. Nevertheless, it should be noted that the nevertheless, deep structural changes in the legislative and amount of felling has markedly increased in all European economic environment would be necessary to promote har- regions since 1990 but not in SW Europe. vester adoption and use [68]. On the contrary, excavator- All types of forests can be found in all three above men- based units, whose popularity is low in North and Central tioned countries of SW Europe, ranging from natural wood- Europe, are quite popular in SW Europe, as a result of their land to remarkably large forest plantations. Fast-growing lower investment cost and their higher operational flexibility plantations aimed at timber or wood-pulp production, such [69 ]. Italy is an exemplary case, with three out of every four as those of poplar in the Po valley, have a rotation period harvester and processor heads mounted on adapted, often of around 10 years, whereas other plantations focused on pre-owned, excavators, indicating a low willingness to invest the production of particularly valuable timber (e.g. walnut, in newer machines in an effort to minimise the associated maple, ash and cherry) have considerably longer rotation financial risk [70]. In this section, representative studies on periods [62]. Plantations of eucalyptus in Central-West Por- mechanised harvesting of broadleaved tree species were car- tugal have been identified as one of the most intensively ried out in Italy, Portugal and Spain. managed forested areas in Europe [63]. Large plantations Magagnotti et al. [71] compared two strategies for chip have also been established in Spain following the decision and firewood production at two technological levels of to increase the share of energy from woody biomass to the mechanisation in thinning operations in Italy. Thinning was national energy mix [64]. carried out with two methods: as a whole tree system (WTS) Coppice forests are widely distributed in SW Europe. Dif- in partially mechanised operations and as the short-wood- ferent management strategies are implemented in the region, system (SWS) in CTL technology. In the WTS, trees were including the conversion of coppice forests to high forests, initially felled and gathered in bunches of v fi e to eight pieces which, given that it is a long and expensive activity, is unat- by a 13-tonne excavator equipped with a chainsaw felling tractive to private owners. Clear-cutting is allowed in some head and then extracted with a 75-kW farm tractor equipped cases, but law requires that some stands are left to favour with a log grapple. In the mechanised treatment, felling, pro- seed production and sprout regeneration from old stumps cessing and stacking were performed in one sequence by a [62]. Given the ecosystem services provided by coppice for- harvester, based on a 13-tonne wheeled loader. All manual ests, especially in terms of soil protection from erosion, cop- operations were carried out by chainsaw. The best results pices are gaining in importance, yet their utilisation remains were achieved with mechanised harvesting, which caused problematic. In most cases, a medium level of mechanisa- less stand and soil damage compared with manual harvest- tion is implemented, consisting of motor-manual felling ing. In mechanised WTS and SWS, higher productivities and mechanised extraction. The extent of mechanisation is were achieved than with the motor-manual methods (15.48 −1 −1 −1 highly variable, ranging from limited on steep terrain to fully t PMH vs 9.27 t PMH in WTH and 5.35 t PMH vs 0 0 0 −1 mechanised in productive poplar sites like in the Po valley 0.87 t PMH in SWS). In terms of cost, WTS was practi- −1 −1 [62]. In most cases, clear-cutting is applied to limited areas cally the same (5.8 € t for manual vs 6.1 € t for mecha- −1 in natural forests, as in the case of light-demanding species nised); however, mechanised SWS (22.4 € t ) contributed −1 (larch and pines), in order to meet the ecological require- to a significant cost reduction over manual SWS (34.9 € t ). ments of these species and facilitate the natural regenera- The mechanised thinning of walnut plantations was also tion of the stands. On the contrary, selection and shelter- examined in Italy [72]. The authors tested two low-invest- wood harvesting systems are strongly encouraged. Coppice ment fully mechanised operations for producing chips (T1) harvesting technology has evolved in the last decades [30]. or traditional firewood (T2) from the thinning of walnut In these stands, mechanical felling and processing can be plantations. In the first thinning operations (T1), a 4-tonne applied, and there is a trend of increasingly large machines skid-steer loader equipped with a disc saw felling head was in coppice operations, as is occurring in high forests and used to fell alder trees and accumulate them in bunches of plantation operations [65]. However, lighter and less special- five to eight pieces, which were later extracted by a farm ised machinery than that used in high forests has been used tractor with a log grapple. In the second treatment (T2), a so far in coppice forests. Thus, relatively cheap and versatile 95-kW farm tractor equipped with a hydraulic loader and a general-purpose machines (excavators, light forwarders and small-scale stroke harvester was used to fell and process the farm tractors) continue to make up the largest part of coppice trees. The same machine was later converted into a forward- machine fleets, compared with heavier and more expensive ing unit by replacing the harvester with a log grapple and forest machinery [30]. attaching a forestry trailer to the tractor. The equipment used 1 3 10 Current Forestry Reports (2022) 8:1–19 −1 −1 in T1 was less costly than in T2 (54.0 € h vs 88.5 € h ) mechanised whole tree system (WTS), which included chip- −1 and offered a higher felling productivity of 11.74 t PMH ping at the landing; 2) a fully mechanised CTL harvesting −1 compared with 2.40 t PMH . Furthermore, mechanised system for firewood; and 3) a semi-mechanised CTL sys- firewood harvesting, as examined in T2, was financially less tem with manual felling and bunching. The biomass removal effective than traditional motor-manual operations. Given rate from heavy thinning ranged from 34.7 to 44.1 oven dry −1 the price levels during the data collection period, small- tonnes (odt) ha for WTS, much higher than the range of −1 scale mechanised chipping was more profitable than motor- 11.6–30.0 odt ha obtained in CTL trials, a result that may manual firewood production along the full tree size range. be partially attributed to the larger average DBH in WTS. Chipping achieved a financial profit, even with smaller trees The WTS reached maximum productivity rates of 3.9 odt −1 than used in firewood production, suggesting that early thin- PMH for the felling and bunching operation and 6.9 odt −1 ning operations can be economically viable when they are PMH for the forwarding operation. The mechanised CTL carried out in a timely manner before the nurse trees overtop harvesting method achieved a lower productivity range of −1 the crop trees. 0.5–1.3 odt PMH for the harvesting operation. Motor- A harwarder is a combined machine used for timber cut- manual felling and cross-cutting in the CTL system resulted −1 ting, processing and forwarding. A small and a large har- in a productivity range of 0.7–1.9 odt PMH . Manual −1 warder (SH and LH) were tested during thinning in hard- bunching results ranged from 0.8 to 1.0 odt PMH . The wood plantations established on agricultural land in Italy semi-mechanised CTL performed best in terms of firewood −1 [73]. Two treatments were carried out: whole tree sections unit cost, at 62.0 € odt for trees with a DBH of 10 cm −1 (WT) or integrated harvesting (IH) – firewood logs joined compared with 85.2 € odt for the fully mechanised CTL with tree tops. The thinning resulted in a yield of 45 t system. The chip production cost at the landing with the −1 of fresh biomass per hectare. The average gross produc- WTS (average DBH = 10 cm) was 65.3 € odt . tivities of the SH and the LH during the WT harvesting Poplar tree plantations are often established in sites with −1 treatment were 3.46 and 2.77 t PMH , respectively. The moist soil. Forest machine operation performance has been SH was more efficient at felling and loading, while the recognised as being dependent on soil moisture. Tavankar LH was more efficient in the terrain transport work. The et al. [75] studied the effects of soil moisture content on productivity of both machines was about 15% lower in productivity, cost and emissions of greenhouse gases (GHG) the IH treatment. The harvesting cost ranged between 18 resulting from different harvesting systems (chainsaw-skid - −1 and 34 € t , with the LH having a higher operational cost der and harvester-forwarder) in two poplar plantations in than the SH. With both machine types, the harvesting cost Italy and one in Iran. Both harvesting systems performed decreased as the stem size of the harvested trees increased. better in dry than in moist sites, with a higher productiv- Suchomel et al. [74] studied the efficiency of four dif- ity by 20–30%. In Italy, poplar plantations are an important ferent harvesters used in Italy for delimbing and bucking source of high-quality veneer logs. Although the conditions of chestnut trees from coppice stands. The machines were favour mechanised operations, the plantation owners indicate as follows: an Arbro 400S on a JCB 8052 excavator, a that mechanised log-making may result in value losses, due Foresteri RH 25 on a CAT 312 L excavator (in two sites), to poor length accuracy, log surface damage and improper a Lako 55 Premio on a JCB JS 180 NL excavator and a grading. Spinelli et al. [12] studied the performance of man- Timberjack 1270B dedicated harvester with a John Deere ual and mechanised log-making in 10 commercial opera- 762C head. Trees were processed at the landing in order to tions, in terms of occurrence and severity of possible value minimise the impact of machine movement on productiv- losses due to product degradation. Mechanised processing ity. The processors reached high productivity values rang- performed better with regard to length measurement errors, 3 −1 ing from 5.4 to 19.8 m PMH . Furthermore, the influ- while the frequency and severity of log surface damage were ence of tree form was estimated in the Arbro 400S study. the same for both treatments. The size of the branches and the shape of the stem had a In a study by Magagnotti et al. [69 ], the annual use, significant effect on machine productivity, which could annual harvesting, productivity and fuel consumption of 3 −1 3 reach 2.3 m PMH for stems with a volume of 0.2 m . three purpose-built harvesters were compared with those of The study showed that mechanical processors can be suc- three excavator-based harvesters and processors after moni- cessfully deployed for handling whole chestnut trees from toring for 1 year. All machines were owned and operated coppice stands, and that working at the landing and in by private contractors and were representative of the Ital- coppice clear-cuts can improve the operational efficiency ian machine fleet. Despite the challenging mountain terrain, considerably. annual use ranged from 675 to 1525 h per year, and annual Three harvesting systems were examined in a total of harvesting volume from 3,200 to 27,400 m per year. Pro- 11 sites in Q. pyrenaica Willd. coppice stands in Spain ductivity was lower for excavator-based units (5.9 to 17.4 3 −1 [64]. The harvesting systems included the following: 1) a m PMH ) than for purpose-built harvesters (12.7 to 21.8 1 3 Current Forestry Reports (2022) 8:1–19 11 3 −1 m PMH ). Purpose-built machines offered higher annual structure of processed timber and between planned and com- use (69–83% vs 48–69%), and reduced fuel consumption pleted production revenues [81]. These differences mean −1 −1 (8.4–15.3 l PMH vs 13.1–17.9 l PMH ) compared with that silvicultural operations are often carried out at the cost- 0 0 •• excavator-based machines. effectiveness limit [18 ]. Timber extraction is mechanised: Ferrari et al. [76] tried to determine the attitudes of North in all countries the number of skidders is higher than the Italian logging contractors towards mechanised CTL tech- number of forwarders, while felling and processing of timber nology, and to evaluate the potential of machine simulators are mainly motor-manual [82, 83, 84]. when introducing mechanised harvesting for prospective In SE Europe, secondary traffic infrastructure is divided users. In this context, a total of 74 valid interviews were into skid roads, i.e. constructed trails, on sloped terrain and carried out on study participants who had previously tested skid roads in lowland forests. The distance between skid a forwarder simulator. The respondents were aware of the roads usually corresponds to the skidder’s winch rope length mechanised CTL technology potential, both in terms of and usually varies due to difficult terrain conditions, mainly productivity and safety. Respondents employed in firewood slope cong fi uration and river networks. It is generally agreed −1 production were keener on the use of CTL technology. The that 200 m ha is a dense road network on steep terrain main obstacles to the expansion of mechanised CTL tech- in forests (managed in selection cutting) of European fir nology in Italy at the time of the study were financial rather (Abies alba Mill.), Norway spruce and European beech [85, than technical. Thus, simplified low-cost machines specially 86]. In lowland (even-aged) forests (in parts of Croatia and designed for firewood production would be very attrac- Serbia) where forwarders are in use, the distance between tive to Italian firewood contractors. As modern machinery strip roads is usually 20–25 m. Machines are required to stay makes use of computer technology, younger contractors are solely on the strip road network, minimising soil and stand expected to be more interested in them. The promotion of disturbance. mechanised harvesting can be enhanced by the use of simu- Motor-manual cutting dominates in SE Europe, mainly lators; however, new approaches that would maximise their due to the diverse terrain and stand conditions and often benefit and compensate for their large cost must be deployed. due to the ownership structure affecting the introduction and use of CTL technology [87]. The large share of natural South‑East Europe forests rich in broadleaved species with a large DBH, selec- tion cutting and costs of motor-manual harvesting also limit In South-East (SE) Europe, 32% of the land area is forested wider use of CTL technology [88]. At the beginning of the (40.887 mln ha). The average growing stock in this area is twenty-first century, some SE European countries had an 3 −1 116 m ha , and in the last 30 years, the growing stock has integral and controlled introduction of fully mechanised fell- increased by 1.74% (Table 1, [23]). In SE Europe, 78% of the ing in cooperation with all the essential forestry stakehold- forested area is under natural regeneration and expansion, ers [89, 90]. There were also previous applications of CTL while some countries such as Croatia and Slovenia reported technology in the 1990s, primarily associated with salvage a share of >80%. High forest is a common management sys- felling in storm-damaged forests [91] or in clear-cuts of pine tem, and in most forest stands, beech accounts for one-third (Pinus sp.) and Douglas fir (Pseudotsuga menziesii (Mirb.) or slightly more of the entire growing stock. Bončina and Franco) [92]. At that point, some authors have reported that Čavlović [77] state that presence of beech indicates close- harvesters could be successfully applied in thinning and to-nature management in Croatia, especially when compared clear-cutting operations in coniferous cultures and planta- with countries where beech dominates other potential for- tions of fast-growing deciduous species, as well as in pure est vegetation. Most SE European countries, i.e. Slovenia, alder (Alnus sp.) and ash (Fraxinus sp.) stands, just as effec- Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, tively as in spruce (Picea sp.) stands. In other even-aged Albania and partially Croatia, manage beech forests by deciduous forests (e.g. oak and beech), the boundary fac- group selection and/or selection systems, which has pre- tors of application are the dimensions of trees (DBH and served their natural form to a large extent [78]. While in stump dimensions), branching, type and intensity of felling Central and North Europe coppice forests comprise just a and terrain conditions [89]. The authors highlighted that the small share of the total forest area, this forest type covers a use of harvesters is questionable in selection cutting, due to large part of the forest area in some countries of SE Europe, the management type and felling dimensions of the trees. such as North Macedonia 59%, Serbia 65% and Greece 65% Krpan and Poršinsky [89] concluded that the goals of fully [79, 80]. mechanised felling are the following: raising productivity, Climatic extremes have caused major problems with sus- lowering production costs, improving ergonomic aspects and tainable forest management that affect the quality of forest avoiding a labour crisis in forest operations. Today, 20–30 products (i.e. roundwood) in SE Europe, which has resulted years later, fully mechanised felling has become a regular in differences between the planned and produced assortment feature in limited areas of SE Europe. 1 3 12 Current Forestry Reports (2022) 8:1–19 Forest operations carried out with modern technolo- deciduous forests. As a result, in Slovenia, [87] reasearch gies are increasing in SE Europe, the experience gained was carried out leading to the evaluation of standard time- by forestry companies and the forestry profession is grow- tables for the most frequent commercial use of harvesters ing, machines and technology solutions on the market are in thinning operations of coniferous and broadleaved trees. very diverse [91]. However, the number of published papers The authors reported that, in the case of broadleaved forked and completed studies regarding mechanised harvesting in trees, there were frequent difficulties with tree processing— broadleaved stands in SE Europe is still relatively small, and the feeding rollers and cutting knives of the harvester head the experiences presented below come from Croatia, Serbia did not develop sufficient force for the successful cutting of and Slovenia. branches. Harvesters were only three times more efficient Shortly after the first introduction of harvesters in 2001 in than motor-manual cutting. In another study in Slovenia in coniferous stands in Croatia, it was reported that CTL tech- which the share of harvester use against motor-manual har- nology could be effectively used in soft broadleaved stands vesting was considered, it was discovered that in salvage i.e. willow (Salix sp.) and alder (Alnus sp.) [93]. The study, logging harvester use was more frequent than in standard, which used a Timberjack 1270B harvester, was carried out planned harvesting, where more or less half of the timber in a 23-year-old willow stand with a mean felling tree DBH volume was cut with harvesters [96]. of 25 cm and a volume of 0.5 m . Machine productivity In Serbia, according to personal communication with 3 −1 was 17.5 m PMH , and clear-cutting, higher felling den- Stojnić (2021), harvesters are used mainly for pine and pop- sity and larger tree dimensions had a positive impact on lar stands. Earlier studies from Serbia, [11] demonstrated the machine productivity. In contrast, large crowns, preparation effect of forks on the productivity of a John Deere 1470D of the site for harvester operation (removal of a thick layer ECO III harvester in poplar plantations. The average maxi- 3 −1 of shrubs) and an inexperienced (in broadleaved stands) mum productivity ranged from 30.3 to 34.7 m PMH , harvester operator were detrimental, and minimisation of depending on the working method. Harvester productiv- these factors would enhance harvester productivity to 27.5 ity was significantly affected by stem dimensions, within 3 −1 m PMH . In the same year, [94] researched mechanised an average DBH of 40.4 cm and an average net volume of 3 −1 felling in 80-year-old thinned stands of sessile oak (Quercus assortments per stem of 1.55 m stem . petraea (Matt.) Liebl.), European beech and European horn- The first applications of fully mechanised systems in SE beam with the same harvester in Croatia. The researched Europe date back to the 1990s to demonstrations from for- stands had more or less similar stand features: growing stock eign contractors and were associated primarily with salvage 3 −1 3 −1 310 m ha and harvesting intensity 30 m ha . Trees too cutting in storm-damaged forests [91] or conifer monocul- thick for the harvester head were cut by a chainsaw operator, tures [89]. Since 2000, fully mechanised cutting has been as were trees with large crowns. In the felling time structure, used increasingly by contractors (mainly in Slovenia and the harvester share was 81% and 19% of the remaining time Croatia), mostly by private forest enterprises. Krč [91] was used for chainsaw operation. The authors concluded that reported that in the Slovenian Forestry Service, companies the average productivity of felling and processing achieved and research institutions held many workshops to promote by the joint operation of a harvester and chainsaw was 14.5 mechanised cutting. The author concluded that Slovenian 3 −1 m PMH . entrepreneurs prefer investing in more universal machines, According to personal communication with Poršinsky due to the greater chance of effective amortisation. Beguš (2021), the number of harvesters working in Croatia today and Krč [90] stated that the introduction of mechanised cut- is >40. If used in hardwood stands, they are usually involved ting in Slovenia was planned and its course was directed in late thinning and preparatory felling operations (mostly in an effective way by workshops held from 2002 to 2018 with European hornbeam), often in combined mechanised [96]. Slovenia was involved in the Quality Forest project and motor-manual cutting, due to the larger butt swelling of (2017–2019), which addressed the challenge of elaborat- trees with a larger DBH, large crowns and thick branches. ing new professional qualifications, focusing mainly on the Vusić et al. [95] also researched mechanised timber harvest- European Chainsaw Certificate, but also on carrying out tree ing in Croatia by a Timberjack 1470D harvester in 80-year- felling and processing with harvesters. According to Marčeta old European hornbeam and European beech harvesting et al. [97], the use of a chainsaw and skidder is the most sites, and concluded that European beech trees with a DBH common harvesting system in Bosnia and Herzegovina. The >52 cm (considering butt swelling) had to be felled and authors promoted the planning of harvesting operations and processed motor-manually. investments with new CTL technologies and improved work- An increase in the use of fully mechanised felling in both ing methods using GIS and the Analytic Hierarchy Process coniferous and deciduous stands was observed in the past (AHP) method. They proposed that using the AHP method, decade in Slovenia [91]. An expansion of harvester use in integrated with GIS software, would lead to improvement deciduous stands in 2009 was due to harvesting in younger in the planning of forest operations, introduction of modern 1 3 Current Forestry Reports (2022) 8:1–19 13 technologies to replace traditional forestry practice and ulti- Europe than in the other regions. In the analysed latest pub- mately selection of the optimal harvesting system. lished research, investigations into whether applications of Previous research on conifers in SW Europe already dem- multi-tree harvesting lead to higher productivity are com- onstrated how tree characteristics, such as forks, can nega- mon. At the same time, there are published findings on the tively affect productivity, by up to 70% for trees of 10 cm difficulties of harvesting broadleaved species with sweep. DBH and by up to 50% for trees of 40 cm DBH [87, 88]. Slo- Also, it is reported that keeping stable log length is chal- venian experiences shown that large, developed crowns have lenging. It can be concluded that broadleaved trees in North a negative influence on productivity, because the harvester’s Europe are characterised by rather thin branching and lim- head is not able to develop a sufficiently high velocity for ited stem sweep in comparison with trees in Central Europe. effective delimbing [89]. Further Slovenian research [98] Another argument for the influence of these morphological indicated that time consumption per unit product should be tree characteristics is that even though CTL technology has determined to compare the economic efficiency of different been developed for large-scale use in North Europe, there is technologies, and that the direct relationship between prod- no evidence of scientific findings leading to improved effi- uct output and time input is productivity. When comparing ciency of broadleaved species harvesting with CTL methods. the productivity of fully mechanised harvesting systems in CTL technology application seems to remain a major chal- coniferous and broadleaved stands, other influencing factors lenge for Central European countries. should be taken into account, such as stem form (multi-stem, Central-West Europe is characterised by the second single-stem), forking, crown size, share of thick branches, largest average growing stock of all European regions, butt swelling and stem sweep, all of which negatively with a large (44.9%) share of broadleaves. In this region, affect productivity. In a recent study, it was observed that a there is an increasing interest and demand in all countries mixed stand (60/40 coniferous to broadleaved) significantly for mechanised hardwood logging, which is leading to affected the reduction of harvesting productivity, highlight- the development of new technologies. However, most of •• ing the importance of operator experience [99 ]. them are produced individually by small manufacturers. The main factor driving increases in the share of broad- leaved stands is climate change and its associated impacts Conclusions i.e. shifts in species, increasing safety risks and economic effects. From a technical point of view, it is necessary to Findings from the latest research on harvester applications in further adapt the harvester head to handle large crowns broadleaf-dominated stands indicate that there are different of hardwood species, especially those with forks and challenging factors in different European regions (Table  2). thick branches. Ribbed knives for harvester heads were In North Europe, difficulties with harvester use for broad- tested, which lead to higher productivity. At the same time, leaved species were observed in the multi-tree harvesting machines should not become too large, since there is a of trees with sweep; other difficulties were in accuracy of trend towards using small and flexible machines, mainly log length, while in Central (West and East) and South-East for soil protection reasons. Given the current developments Europe, harvester use for broadleaved species has more and the increasing pressure to provide hardwood timber in potential limitations. The development of harvester heads an economically efficient, safe and environmental-friendly dedicated to broadleaved species is mainly focused on Cen- manner, it can be expected that the development will con- tral Europe, where the share of broadleaved species and tinue to progress. their particular morphological features (thick branches and Central-East Europe is characterised by the largest sweep) are a major challenge for CTL technology. There growing stock of all European regions, with a very large have been research projects completed on this topic: in the (47.4%) share of broadleaves. Wider harvester use occurs last 15 years, there were a few larger initiatives leading to the mainly in two countries, Poland and the Czech Repub- design and development of harvester heads for broadleaved lic, where up to ca. 40% of timber is harvested by CTL species, with participation from institutions and universities technology. There are recognised causes of limitations to in France, Germany and Poland. There are currently no initi- wider harvester use, i.e. mountainous areas and broad- atives, but the formation of new ones is highly recommended leaved species, due to their morphological features (mainly because we currently manage and develop forests in a way sweep and thick branches), that lead to lower quality of that is different from how it was done in the last century. delimbing, lower length accuracy, or large tree tops left North Europe is the region with the highest forest cover, unprocessed. For this reason, it is recognised that harvester but with the smallest share of broadleaves. The growing heads require adjustments in design and construction to stock is average in comparison with other regions. A large make timber processing more effective. It is also recog- share of coniferous species is advantageous for wide use of nised that e.g. birch in CE Europe has different features to CTL technology, and this method is more popular in North birch in Scandinavia or other parts of North Europe. Birch 1 3 14 Current Forestry Reports (2022) 8:1–19 1 3 Table 2 Conclusion highlights for each European region North Europe Central-West Europe Central-East Europe South-West Europe South-East Europe The most forested area in Europe, An increase in broadleaf-dominated The largest growing stock of all A large share of broadleaved species The largest share of broadleaved spe- with the smallest share of broad- or mixed stands can be expected. European regions. and the lowest growing-stock den- cies as growing stock. leaved species. Low share of CTL technology, due CTL with a maximum share of 40% sity of all European regions. Partially mechanised harvesting Highly mechanised forest opera- to small clear-cuts, but good, in the region. Although the growing stock has systems are dominant. tions. extensive strip road system. Broadleaved species limit harvester increased, the number of felling Characteristics of broadleaved species Studies focused on the effectiveness Harvester productivity is lower than use. operations has decreased since limit the use of harvesters: large of multi-tree harvesting of broad- in coniferous stands. Use of inno- Scientific projects have been 1990. butt swelling, thick branches, forked leaved species. vative ribbed knives in harvester completed leading to selection In many cases forest machinery can trees, large and developed crowns. Log length accuracy of multi-tree head increased productivity. of the best harvesters for broad- be employed, but promotion and Buck-to-quality method is applied, in harvesting needs improvement. Current research focuses on machine leaved species. Initiatives have an increase in growing stock have which the forester uses wood defects No studies on the difficulties of development for the processing of been undertaken for new designs to be introduced first. and dimensions to determine the harvesting broadleaved species. large hardwood crowns (patented). of harvester heads dedicated to Incremental innovation is applied, cutting position of round wood. Many individual developments by broadleaved species (patented). and financial incentives are Harvester productivity is higher in small manufacturers. Harvester productivity tends to be deemed necessary to boost forest coniferous stands. An increase in supply and demand is lower in broadleaved stands in mechanisation. Expected growth in the number of expected. comparison with coniferous stands. qualified and experienced harvester In contrast, higher productivity can operators for broadleaved stands. be achieved when larger tree tops are left without processing. Limited harvester use for hard- woods, difficulties with: process- ing in top tree parts, delimbing and log length accuracy. Further improvements of harvester heads are expected. Current Forestry Reports (2022) 8:1–19 15 in CE Europe frequently has sweep and thicker branches, in broadleaved stands is the economically important buck- which make it more difficult to process. Therefore, sci - to-quality method, in which foresters define timber assort- entific projects were carried out in last two decades in ments and select the most valuable ones. Similar to in other which selection of the best harvester heads for broadleaved regions, there is an increasing demand for hardwood; there- species was an objective. Other projects were carried out fore, it can be concluded that in the future, the development (mainly in co-operation with scientists from Central-West will move to fully mechanised harvesting operations. Europe) and focused on the construction of heads with Acknowledgements The authors thank Mr. Julian Muhmenthaler from features making the processing of hardwood easier (e.g. WSL for supporting the French literature review. The authors are grate- the CTL 40 HW head and new patent granted in October ful to Professor Tomislav Poršinsky, PhD from the Faculty of Forestry 2021: Harvester head for hardwood). In general, experi- and Wood Technology, University of Zagreb, and Mrs. Silvija Zec, ences with harvester use for broadleaved species indicate president of the Croatian Chamber of Forestry and Wood Technology Engineers, for sharing information on the current number of harvest- that productivity is lower than in harvester use with coni- ers in Croatia. fers. Higher productivity can be achieved only when large tree tops are left without processing. When using harvest- Funding The publication was co-financed within the framework of ers for plywood, damage of the outer layer was observed, the Polish Ministry of Science and Higher Education’s programme: “Regional Initiative Excellence” in the years 2019–2022, Project No. which can lead to economic loses and a lower quality of 005/RID/2018/19. logs. Harvester use for broadleaved species has become unavoidable, mainly due to significant changes in forest Data availability The authors confirm that the data supporting the find- management leading to mixed or broadleaf-dominated ings of this study are available on request. stands and plantations. Therefore, it is expected that in the future, due to increases in broadleaved species shares in Declarations stands, improvements of harvester heads will be necessary to improve the effectiveness of CTL technology. Conflict of Interest The authors declare no competing interests. The region of South-West Europe represents an inter- Human and Animal Rights and Informed Consent This article does not esting case; despite having quite a large (44.4%) share contain any studies with human or animal subjects performed by any of broadleaves in the European context, the region also of the authors. has the lowest growing-stock density. This fact inevitably affects the profits of forest entrepreneurs who are reluctant Open Access This article is licensed under a Creative Commons Attri- to invest in capital-demanding forest machines. Instead, bution 4.0 International License, which permits use, sharing, adapta- local innovations are applied in the form of excavators tion, distribution and reproduction in any medium or format, as long equipped with harvester heads. However, their future as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes deployment will depend on their fuel efficiency, where were made. The images or other third party material in this article are they are outperformed by more expensive, purpose-built included in the article's Creative Commons licence, unless indicated harvesters. In SW Europe, past research on mechanised otherwise in a credit line to the material. If material is not included in harvesting of broadleaved species has largely focused on the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will coppice forests, agroforestry systems and firewood produc- need to obtain permission directly from the copyright holder. To view a tion. More research on mechanised harvesting is needed, copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . as well as policy tools to promote and ease investments in CTL technology. In the face of climate change and the declining forest workforce, mechanised harvesting of References broadleaved stands seems to be the missing link between more intensive and efficient forest utilisation. Papers of particular interest, published recently, have South-East Europe is characterised by the largest share of been highlighted as: broadleaved species in growing stock, and it has the greatest • Of importance (+1.74%) increase of annual growing stock. Even though the •• Of major importance share of fully mechanised forest operations in this region is increasing, partially mechanised harvesting systems still pre- 1. Martin P, Lapeyre D, Douchet O, Restoy G, Guegand G. Récolte mécanisée des taillis en bois ronds (Mechanised harvesting of vail. 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Since it is expected that harvesters will be used more Efficiency of harvesters in the culture of soft broadleaf trees. and more in broadleaved stands, results of this study could Šumarski List. 2004;128(5–6):233–44. be used to show a more holistic approach of close-to-nature 94. Krpan AP, Poršinsky T, Stankić I. Efficiency of mechanical fell- forestry and its future implications for harvester operators.) ing and processing in soft and hardwood broadleaved stands; Part 3: Efficiency of harvester in natural thinning stands of hardwood Publisher's Note Springer Nature remains neutral with regard to broadleaf species. Šumarski List. 2004;128(9–10):495–508. jurisdictional claims in published maps and institutional affiliations. 1 3

Journal

Current Forestry Reports – Springer Journals

Published: Mar 1, 2022

Keywords: Deciduous tree species; Forest operation; Hardwood; Harvester; Harvester head; Productivity; Thick branch

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