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Community composition, structure and management of subtropical vegetation of forests in Meghalaya State, northeast India

Community composition, structure and management of subtropical vegetation of forests in Meghalaya... International Journal of Biodiversity Science, Ecosystem Services & Management Vol. 6, Nos. 3–4, September–December 2010, 157–163 Community composition, structure and management of subtropical vegetation of forests in Meghalaya State, northeast India O.P. Tripathi* and R.S. Tripathi Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli 791 109, Itanagar, Arunachal Pradesh, India The study was conducted in three major forest types in Meghalaya State, northeast India, to characterise soil properties, community composition, tree population structure and management. Random sampling was conducted in each representative forest patch for community and soil analysis. Soils of pine forest were more acidic and relatively low in nutrients compared to evergreen and semi-evergreen forests. Tree species richness was higher in broadleaf forests than in needle-leaf forests. The dominance–distribution pattern was log normal in the former forests and was like a broken stick in the pine forest. The Shannon diversity index was higher in broadleaf forests than in pine forest, while the Simpson dominance index showed a reverse trend to that of the diversity index. Distribution of stand density in different DBH classes revealed that young individuals constituted the maximum, with a declining trend as trees matured. All three forest types showed dominance of tree seedlings and a low population density of saplings and adult trees, resulting in a pyramidal structure, indicating that the period between seedling and sapling stage was most critical in the tree life cycle, with maximum mortality during this last period. The findings of this study can help to more sustainably manage the three forest types, both in the study area and in areas elsewhere that have similar edapho-climatic conditions, and aid in conserving regional biodiversity, although more ecological research is needed. Keywords: broadleaf forest; dispersion pattern; diversity and dominance indices; needle-leaf forest; population structure; soil properties; stratification Introduction stand is a major concern for forest conservation (Foster et al. 1996). Tropical and subtropical forests have attracted the atten- The varied physiography, soil and climatic conditions tion of a large number of researchers, who have carried of northeast India are responsible for the high abundance out comprehensive studies on forest community organisa- of several forest types. The state of Meghalaya, in the tion and dynamics and estimated species richness, biomass northeastern Indian biogeographic zone, constitutes the and productivity (Condit et al. 1996, 2000; Aiba and junction of paleo-arctic, Indo-Malayan and Indo-Chinese Kitayama 1999; Tripathi and Khongjee 2010; Tripathi et al. biogeographic realms. The diverse ecological conditions, 2010). Forest structure and composition are strongly cor- for example, wide variation in rainfall, temperature, alti- related with environmental factors, such as climate and tude and soil, and the inaccessible humid areas of the topography (Currie 1991). Tree species diversity is an state, support luxuriant growth of tropical and subtropical important aspect of forest ecosystem diversity (Rennolls vegetation, which is rich in Angiosperms. The subtropi- and Laumonier 2000). Tree species inventories at defined cal evergreen and semi-evergreen forests of the state cover sites and in minimum diameter at breast height (DBH) large areas, with forest patches confined to remote areas classes provide a reliable instrument to indicate diversity of with complex terrain that have been less influenced by the stand. Quantitative floristic sampling also provides the humans. However, pine forests are secondary in nature, necessary context for planning and interpreting long-term where succession has been arrested due to a complex inter- ecological research (Phillips et al. 2003). action of biotic and edaphic factors. These forests are Diversity of a community can be assessed using several mostly confined to the higher reaches of Khasi and Jaintia non-parametric measures, such as the Shannon, Simpson Hills district and are highly fragmented. The impact of and Margalef indices, and these measures have gained shifting cultivation is lower in evergreen forests than in credibility (Magurran 1988). Besides species diversity, semi-evergreen forests, as these forests are confined to less studying abundance of species within communities helps in complex terrain (Tripathi 2002). determining common and rare species. Population studies Disturbance creates opportunities for species to claim in forest ecosystems have been used to deduce the health previously unutilised space and resources. Individuals and of a population, any past changes and to predict future species may differ in their ability to secure these resources changes in species composition by examining the size class and, as a result, disturbance may lead to a shift in distribution of the woody species (Read et al. 1995). Low species composition. Forest microclimates, and therefore numbers of seedlings and saplings of a species in a forest *Corresponding author. Email: optripathi@yahoo.com ISSN 2151-3732 print/ISSN 2151-3740 online © 2010 Taylor & Francis DOI: 10.1080/21513732.2010.539987 http://www.infomaworld.com 158 O.P. Tripathi and R.S. Tripathi recruitment conditions, change after a disturbance. In gen- (<1 m high) and saplings (<15 cm DBH and >1 m high) eral, removal of the forest canopy results in more direct were studied by laying 30 quadrats of 2 m × 2min solar radiation, higher temperatures and reduced humidity. all three forest stands. The nomenclature for the species The primary reasons for forest destruction are cattle follows regional floras (Haridasan and Rao 1985–1987). grazing, over-exploitation for medicinal and ornamental Frequency, density, basal cover and importance value index plants and encroachment into forested area for cultiva- were calculated according to Misra (1968) and Mueller- tion. The objectives of the present study were to anal- Dombois and Ellenberg (1974). The Whitford index was yse and investigate soil characteristics, plant diversity, used to study the distribution patterns of species (Whitford community organisation and population structure of sub- 1948). Various diversity indices were calculated following tropical evergreen, semi-evergreen and pine forests of Magurran (1988). Population structure of forest stands was Meghalaya. studied at community level following Khan et al. (1987). The intensity of disturbance was calculated based on the number of cut stumps divided by the total number of stems of all tree species including cut stumps. Study area The study was conducted in three selected forests to characterise their floristic composition and population structure. Representative forest stands, that is, subtropi- Results ◦  ◦ cal evergreen (25 27 N, 90 19 E, 1425 m a.s.l.), semi- Soil characteristics ◦  ◦ evergreen (25 14 N, 91 43 E, 1475 m a.s.l.) and pine Pine forest occurs on well-drained, porous acidic soil with ◦  ◦ (25 32 N, 91 53 E, 1900 m a.s.l.) were selected in each a low nutrient concentration. Soils of pine forest were more forest. Soil samples were collected randomly from two acidic and had relatively low organic carbon, organic mat- (0–10 cm and 10–20 cm) depths at ten places on an annual ter, nitrogen and available phosphorus than the evergreen basis from the selected forest stands and were mixed thor- and semi-evergreen forests. Concentrations of all these oughly to obtain a composite sample. These samples were constituents were higher in the upper (0–10 cm) than the used to determine the pH, soil organic carbon, nitrogen lower (10–20 cm) soil layer in all the three forest stands and available phosphorus using the methods given in Allen (Table 1). et al. (1974) and Anderson and Ingram (1993). The state has a monsoon climate. The climatic vari- ables like temperature, rainfall and humidity vary widely from place to place due to the wide variation in topo- Plant diversity and stratification graphy. Based on atmospheric conditions, the year may Tree species richness was higher in broadleaf than in be divided into summer (March end to mid-May), rainy needle-leaf forests. A total of 76, 77 and 26 tree species (mid-May to September), autumn (October and November) were recorded in a 1-ha sampled area in evergreen, semi- and winter (December to February). The annual rainfall evergreen and a 0.3-ha area in pine forest, respectively. The varies widely, from about 1600 mm (Umiam, Ribhoi) to number of shrub species was higher in the semi-evergreen over 11,463 mm (Mawsynram, East Khasi Hills). The mean forest, and there were more herbaceous species in pine ◦ ◦ minimum and maximum temperature are 5 C and 33 C forest than evergreen forest (Table 2). and relative humidity is 56–92%. Stratification was distinct in the evergreen and semi- evergreen forests, with trees distributed in three distinct strata: canopy (>15 m), sub-canopy (8–15 m) and treelet Methods (2–8 m) layers. However, there was no clear stratification Twenty-five quadrats of 20 m × 20 m were randomly laid in in the pine forest. The canopy layer contained 13 species in the evergreen and semi-evergreen forests and 30 quadrats both evergreen and semi-evergreen forests, but was almost of 10 m× 10 m were laid in the pine forest, and all indi- exclusively composed of Pinus kesiya in the pine forest; viduals (>15 cm DBH) were recorded. Tree seedlings however, a few broadleaf trees, for example, Quercus sp., Table 1. Soil characteristics of subtropical evergreen, semi-evergreen and pine forests. Evergreen Semi-evergreen Pine Soil properties/Soil depth 0–10 cm 10–20 cm 0–10 cm 10–20 cm 0–10 cm 10–20 cm Soil moisture (%) 31.8 32.3 34.1 37.2 26.3 30.1 pH 5.80 5.41 5.3 5.1 5.12 5.10 Soil organic carbon (%) 2.62 1.84 2.18 1.64 2.38 1.60 Soil organic matter (%) 4.52 3.17 3.76 2.83 4.10 2.76 Total nitrogen (%) 0.42 0.35 0.27 0.19 0.17 0.14 −1 Phosphorus (µgg ) 28.7 25 31.7 24.5 17.2 15.1 International Journal of Biodiversity Science, Ecosystem Services & Management 159 Table 2. Community characteristics of the forests of and Helicia excelsa in evergreen forest, Psychotria errat- Meghalaya. ica, Symplocos paniculata, Adenia trilobata, Rhus javan- ica and Achronychia pedunculata in the semi-evergreen Evergreen Semi-evergreen Pine forest and Eupatorium adenophorum, Osbeckia crinita, forest forest forest Thysaenolaena agrostis and Rubus sp. in the pine forest Tree species (>15 cm DBH) (Tripathi 2002). Sample area (ha) 1 1 0.3 The tree seedlings, annual and perennial flowering −1 Density ha 1023 838 1050 plants and ferns constituted the ground layer in the forests. Basal cover 33.3 49.5 37.4 2 −1 The ground vegetation was more (57 species) species (m ha ) Species richness 76 77 26 rich in the pine forest than in the evergreen (44 species) Number of genera 58 56 23 and semi-evergreen (47 species) forests (Table 2). Among Number of families 35 34 17 the most common ground vegetation was Colquhounia Shannon diversity 4.2 4.21 2.19 coccinea, Hypericum laxum, Senecio cappa, Gleichenia index Simpson 0.02 0.02 0.06 sp. and Asplenium sp. in the evergreen forest, Anotis dominance index oxyphylla, Hemiphragma heterophyllum, Davaellia sp., Disturbance index 921 35 Crysopogon aciculatus and Asplenium sp. in the semi- (10%) evergreen forest and Asplenium sp. and Davaellia sp. in Shrub species (5 to <15 cm DBH, >1 m high) −1 the pine forest (Tripathi 2002). Density ha 1747 1608 1953 Species richness 20 23 21 Number of genera 18 20 18 Number of families 13 13 14 Dominance and distribution pattern Shannon diversity 2.77 2.91 2.39 index Life-form spectra showed a preponderance of phanero- Simpson 0.07 0.05 0.12 phytes in broadleaf forests, followed by chamaephytes and dominance index therophytes; pine forests had few phanerophytes (28.4%) Herbaceous species (<1 m high) 2 (Tripathi 2002). The dominance–distribution pattern was Density (100 m ) 1554 2976 1354 similar in evergreen and semi-evergreen forest, with a log Species richness 44 47 57 Number of genera 38 40 49 normal distribution pattern, signifying high equality and Number of families 32 25 28 low species dominance in the community. However, the Shannon diversity 3.40 3.55 3.53 pattern was a broken-stick shape in the pine forest, indi- index cating low equality in the dispersion of dominance of tree Simpson 0.05 0.03 0.04 species (Figure 1). The Shannon diversity index was higher dominance index in the broadleaf forest (4.2) than the pine forest (2.19), Number of tree stumps Note: Disturbance index = × 100. Total number of trees including tree stumps while the Simpson dominance index showed an opposite trend. The diversity index for the shrub and herbaceous Schima wallichii, Myrica esculenta and Exbucklandia pop- layers showed a similar trend to that for woody species ulnea, were found scattered in this forest (Tripathi 2002). richness (Table 2). The under-canopy (2–15 m) was poor in the pine forest, Most (68–95%) plant species in the forest had a but was the most species rich layer in the evergreen and contagious/clumped distribution pattern (Table 3), with semi-evergreen forests, contributing about 80% of total only a few species having regular or random distribution. of species richness. Elaeocarpus rugosus, Castanopsis tribu- the higher contagious distribution revealed that the species loides, Engelhardtia spicata and Duabanga grandiflora in were in patches, and was further supported by the fre- the evergreen forest, Aporusa oblonga, Dysoxylum binec- quency distribution pattern, with most species having a low tiferum, S. wallichii and Ficus sp. in the semi-evergreen frequency. forest were among the most dominant canopy trees. Lauraceae was the most common family, with 11, 10 and five species in the evergreen, semi-evergreen and pine Stand density and basal cover forest, respectively. Euphorbiaceae and Pinaceae were co- dominant in the broadleaf and pine forests. There were Stand density of tree species was higher in the ever- many families represented by a single species in all three green and pine forests (1023 and 1050 individuals per ha) forests. Dominance–distribution curves of the families than in the semi-evergreen forest (838 individuals per ha). showed that only a few families were dominant in broad- Although stand density of semi-evergreen forest was less and needle-leaf forests and large number of families had than the other two forests, the contribution to basal cover low FIV (Tripathi 2002). was higher (Table 1). The stand density in different girth Shrub species were represented by 20, 23 and 21 classes revealed that young individuals (<55 cm DBH) species belonging to 18, 20 and 18 genera and 13, 13 were most common (70% and 78%) and thereafter showed and 14 families in the evergreen, semi-evergreen and a declining trend (reverse J-shaped curves) in broadleaf pine forests, respectively (Table 2). The most common forest. Adult individuals (>95 cm DBH) were represented shrub species were Bridelia retusa, Callicarpa rubella by a few individuals in the broadleaf forest and completely 160 O.P. Tripathi and R.S. Tripathi (a) Evergreen forest Semi-evergreen forest Evergreen forest Pine forest Semi-evergreen forest Pine forest 100 400 (b) 0.1 0 1020 3040 5060 7080 90 Plant species Figure 1. Dominance–distribution of tree species in the subtrop- ical evergreen, semi-evergreen and pine forests. absent from the pine forest. However, in pine forest mature trees (55–95 cm DBH) contributed most to stand density. 15−35 35−55 55−75 75−95 >95 The distribution of basal cover was opposite to that of stand Girth-class (cm) density, that is, mature and adult trees, although less in Figure 2. Density–distribution (a) and basal cover (b) distri- number, contribute most to the basal cover (Figure 2). bution in the subtropical evergreen, semi-evergreen and pine forests. Population structure Mean seedling density (plants 100 m ) was 494, 1341 Glochidion acuminatum, Garcinia pedunculata and Persea and 501 in the evergreen, semi-evergreen and pine duthiei in semi-evergreen forest and Myrica esculenta, forest, respectively. The most common seedlings were Quercus glauca, Lindera leata and Litsea sp. in the pine Ostodes paniculata, Persea duthiei, Macaranga den- forest (Tripathi 2002). ticulata and Engelhardtia spicata in evergreen forest, The mean density of adult trees was 1023, 838 and −1 Cinnamomum tamala, Aporusa oblonga, Celtis tetranda, 1050 individuals ha in the evergreen, semi-evergreen Callicarpa arborea and Ficus racemosa in semi-evergreen and pine forest, respectively. Based on density, all three forest and Eurya acuminata, Combretum acuminatum, forests showed a dominance of tree seedlings and low pop- Lyonia ovalifolia and Zanthoxylum alatum in pine for- ulation density of saplings and adult trees, resulting in an est (Tripathi 2002). The mean sapling density was upright pyramid-type structure. The preponderance of tree −1 −1 3813 stem ha in evergreen forest, 4056 stem ha in seedlings, followed by a steep decline in population den- −1 semi-evergreen forest and 2212 stem ha in pine for- sity of saplings and adult trees indicated that the seedling est. The most common saplings were C. tamala, Citrus to sapling stage was the most critical stage in the life of a medica, Glochidion assamicum and Callicarpa vestita tree, and most mortality (about 93%) occurred during this in evergreen forest, Camellia cauduca, Celtis tetranda, period (Figure 3). Table 3. Distribution pattern of trees, shrubs and herbaceous species in the subtropical broad- and needle-leaf forests. Evergreen forest Semi-evergreen forest Pine forest Distribution pattern Tree Shrub Herb Tree Shrub Herb Tree Shrub Herbs Regular 6(8) 0 6(14) 1(1) 1(4) 5(11) 1(3) 1(5) 5(9) Random 18(24) 1(5) 5(11) 15(20) 2(9) 9(19) 3(12) 4(19) 12(21) Contagious 52(68) 19(95) 33(75) 61(79) 20(87) 33(70) 22(85) 16(76) 40(70) Total 7620447723472621 57 Importance value index Density per hectare 2 −1 Basal cover (m ha ) International Journal of Biodiversity Science, Ecosystem Services & Management 161 a few deciduous species, which shed their leaves dur- Evergreen forest Semi-evergreen forest ing the dry months between February and April, gives a Pine forest semi-evergreen appearance to the forest. The majority of species showed a contagious/clumped distribution in all the forests, which could be attributed to insufficient seed dispersal (Richards 1996), topography and soil factors (Currie 1991). A regular dispersion pattern, as observed in the present study, may be the consequence of direct competition for water and nutrients, allellopathy or frequent disturbance, which largely contribute to the main- tenance of a high level of diversity (Armesto et al. 1986). The change in dominance distribution pattern from log normal in the broadleaf to broken-stick shape in the pine forest indicate a marked shift from high equality to high dominance in the community due primarily to disturbance. The dominance of phanerophytes in broadleaf forests is indicative of a mild and moist climate, as also found by Archibold (1995). Dominance of therophytes followed by phanerophytes in pine forest suggest a transformation of Seedling Sapling Adult mesic habitat supporting broadleaf forests to a disturbed Age group xeric habitat that provides more favourable conditions for annuals and tolerant tree species like Pinus kesiya (Tripathi Figure 3. Overall population structure of the subtropical forests 2002). In general, the higher values for therophytes, the of Meghalaya. more homogenous are the stands (Singh et al. 2006). The girth class composition of stands at high distur- Discussion bance levels resembles a J-shaped distribution (number increases with increasing age), indicating future decline in The selected forest types are the major forest types in Meghalaya State; they cover an area of about 41% of the population. However, at low disturbance, the trend is the total geographical area of the state. These forests are reversed due to the presence of a large number of indi- between 800 and 2000 m a.s.l. The climate is seasonal, viduals in lower girth classes, an indicator of a growing with a 7–8-month rainy season. The evergreen and semi- population (Pandey and Shukla 2001). Selective thinning evergreen forests differ, depending on the species domi- of treelets for firewood and their death due to surface fire nance in the canopy. Evergreen forests are found where seems to be a major cause of loss of young individuals. rainfall is relatively high and soil moisture is favourable for The tree density in the broadleaf forest and its reverse most of the year. The areas with low rainfall support semi- J-shaped distribution in different girth classes could be evergreen vegetation, mainly due to the coarse texture or related to gap phase dynamics, tree regeneration behaviour high slope gradient or both (Tripathi 2002). Human inter- and age of the stand. In the pine forest, density distribu- vention in these broadleaf forests has paved the way for tion in different girth classes seems to be determined by the cumulative effect of natural thinning, selective cutting development of pine forests, which represent the edaphic and surface fires, as these factors cause heavy mortality and biotic climax community on disturbed sites, which are of tree seedlings and saplings. Variations in species rich- seasonally dry and nutrient poor. ness and diversity at a local scale are affected by a number The most noticeable features of the tropical and sub- of complex and interacting variables, including both natu- tropical humid forests are the species richness, hetero- ral environmental factors and human-made changes to the geneity and complex community organisation. Rainfall local environment. At relatively small spatial scales, envi- pattern and temperature regime strongly influence their ronmental variables, such as chemical and physical soil floristic composition, which is further modified by edaphic properties (Fu et al. 2004; Poulsen et al. 2006), topogra- and biotic influences (WCMC 1992). The dominance of phy (Fu et al. 2004; Cielo-Filho et al. 2007) and human families like Lauraceae, Euphorbiaceae, Moraceae and disturbance, such as logging (Brown and Gurevitch 2004) Rubiaceae in the broadleaf forests is similar to tropical rain forest of Pasoh reserve forests in Malaysia and subtropi- and livestock grazing (McEvoy et al. 2006; Dufour-Dror cal forests/sacred forests in Meghalaya (Manokaran et al. 2007) are important drivers of community structure. 1991; Mishra et al. 2004; Tripathi and Khongjee 2010; Tripathi et al. 2010). The soil profile in broadleaf forests is well developed, Conclusions acidic and rich in organic matter and nutrients. The soil in pine forests, however, is more acidic and low in organic All three forest types are found inter-mixed at higher ele- matter and nutrients. The subtropical evergreen forest is vations under similar climatic conditions. However, the richer in species than the evergreen forest. Presence of evergreen forest is mainly in more humid and inaccessible Density per 100 m 162 O.P. Tripathi and R.S. Tripathi areas. In this forest, the tree species richness is lower Condit R, Hubbel SP, LaFrankie JV, Sukumar R, Manokaran N, Foster RB, Ashton PS. 1996. Species–area and species– than in the semi-evergreen forest. Although all three for- individual relationships for tropical trees: a comparison of est types were exposed to different levels of disturbance, three 50-ha plots. J Ecol. 84:549–562. the pine forests on nutrient-poor and relatively dry soil Currie DJ. 1991. Energy and large-scale patterns of animal- and are more disturbed and are lower in tree species richness plant-species richness. Am Nat. 137:27–49. than the other two types. In spite of disturbance, regen- Dufour-Dror JM. 2007. Influence of cattle grazing on the density of oak seedlings and saplings in a Tabor oak forest in Israel. eration of the dominant tree species in the evergreen and Acta Oecol. 33:223–228. semi-evergreen forests is satisfactory, but was poor in the Foster DR, Orwig DA, Maclachalan JS. 1996. Ecological pine forest. Clumped distribution of species was attributed and conservation insights from re-constructive studies of to insufficient seed dispersal, topography and soil factors. temperate old growth forests. Trends Ecol Evol. 11: The change in dominance distribution pattern indicates 419–424. Fu BJ, Liu SL, Ma KM, Zhu YG, 2004. Relationships between a marked shift from high equality to high dominance in soil characteristics, topography and plant diversity in a the community due to cumulative effects of natural thin- heterogeneous deciduous broad-leaved forest near Beijing, ning, selective cutting and surface fire, as these factors China. Plant Soil. 261:47–54. cause heavy mortality of tree seedlings and saplings. Based Haridasan K, Rao RR. 1985–1987. Forest flora of Meghalaya. on the findings of this study, it is evident that human Vol. 2. Dehra Dun (India): Bishen Singh Mahendrapal Singh. disturbances are the main drivers of spatial variation in Khan ML, Rai JPN, Tripathi RS. 1987. Population struc- species richness and population structure. Conservation ture of some tree species in disturbed and protected of regional biodiversity therefore faces major challenges sub-tropical forests of north-east India. Acta Oecol. 8: since it competes with basic demands of local communi- 247–255. ties. 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Effects Dehradun, for financial assistance in the form of a research of anthropogenic disturbance on plant diversity and com- project, and also Prof. A.K. Misra, Head, Department of Botany, munity structure of a sacred grove in Meghalaya, north-east North-Eastern Hill University, Shillong, for providing basic India. Biodivers Conserv. 13:421–436. infrastructure for conducting the research. The authors are grate- Misra R. 1968. The ecology work book. Calcutta (India): Oxford ful to the reviewers for their valuable comments and suggestions, and IBH Publishing. which have improved the manuscript. Mueller-Dombois D, Ellenberg H. 1974. Aims and methods of vegetation ecology. New York: John Wiley and Sons. Pandey SK, Shukla RP. 2001. Population structure of woody References plants in relation to disturbances including NTFP extrac- tion in forests of north eastern Uttar Pradesh, India. In: Aiba S, Kitayama K. 1999. 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Community composition, structure and management of subtropical vegetation of forests in Meghalaya State, northeast India

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International Journal of Biodiversity Science, Ecosystem Services & Management Vol. 6, Nos. 3–4, September–December 2010, 157–163 Community composition, structure and management of subtropical vegetation of forests in Meghalaya State, northeast India O.P. Tripathi* and R.S. Tripathi Department of Forestry, North Eastern Regional Institute of Science and Technology (Deemed University), Nirjuli 791 109, Itanagar, Arunachal Pradesh, India The study was conducted in three major forest types in Meghalaya State, northeast India, to characterise soil properties, community composition, tree population structure and management. Random sampling was conducted in each representative forest patch for community and soil analysis. Soils of pine forest were more acidic and relatively low in nutrients compared to evergreen and semi-evergreen forests. Tree species richness was higher in broadleaf forests than in needle-leaf forests. The dominance–distribution pattern was log normal in the former forests and was like a broken stick in the pine forest. The Shannon diversity index was higher in broadleaf forests than in pine forest, while the Simpson dominance index showed a reverse trend to that of the diversity index. Distribution of stand density in different DBH classes revealed that young individuals constituted the maximum, with a declining trend as trees matured. All three forest types showed dominance of tree seedlings and a low population density of saplings and adult trees, resulting in a pyramidal structure, indicating that the period between seedling and sapling stage was most critical in the tree life cycle, with maximum mortality during this last period. The findings of this study can help to more sustainably manage the three forest types, both in the study area and in areas elsewhere that have similar edapho-climatic conditions, and aid in conserving regional biodiversity, although more ecological research is needed. Keywords: broadleaf forest; dispersion pattern; diversity and dominance indices; needle-leaf forest; population structure; soil properties; stratification Introduction stand is a major concern for forest conservation (Foster et al. 1996). Tropical and subtropical forests have attracted the atten- The varied physiography, soil and climatic conditions tion of a large number of researchers, who have carried of northeast India are responsible for the high abundance out comprehensive studies on forest community organisa- of several forest types. The state of Meghalaya, in the tion and dynamics and estimated species richness, biomass northeastern Indian biogeographic zone, constitutes the and productivity (Condit et al. 1996, 2000; Aiba and junction of paleo-arctic, Indo-Malayan and Indo-Chinese Kitayama 1999; Tripathi and Khongjee 2010; Tripathi et al. biogeographic realms. The diverse ecological conditions, 2010). Forest structure and composition are strongly cor- for example, wide variation in rainfall, temperature, alti- related with environmental factors, such as climate and tude and soil, and the inaccessible humid areas of the topography (Currie 1991). Tree species diversity is an state, support luxuriant growth of tropical and subtropical important aspect of forest ecosystem diversity (Rennolls vegetation, which is rich in Angiosperms. The subtropi- and Laumonier 2000). Tree species inventories at defined cal evergreen and semi-evergreen forests of the state cover sites and in minimum diameter at breast height (DBH) large areas, with forest patches confined to remote areas classes provide a reliable instrument to indicate diversity of with complex terrain that have been less influenced by the stand. Quantitative floristic sampling also provides the humans. However, pine forests are secondary in nature, necessary context for planning and interpreting long-term where succession has been arrested due to a complex inter- ecological research (Phillips et al. 2003). action of biotic and edaphic factors. These forests are Diversity of a community can be assessed using several mostly confined to the higher reaches of Khasi and Jaintia non-parametric measures, such as the Shannon, Simpson Hills district and are highly fragmented. The impact of and Margalef indices, and these measures have gained shifting cultivation is lower in evergreen forests than in credibility (Magurran 1988). Besides species diversity, semi-evergreen forests, as these forests are confined to less studying abundance of species within communities helps in complex terrain (Tripathi 2002). determining common and rare species. Population studies Disturbance creates opportunities for species to claim in forest ecosystems have been used to deduce the health previously unutilised space and resources. Individuals and of a population, any past changes and to predict future species may differ in their ability to secure these resources changes in species composition by examining the size class and, as a result, disturbance may lead to a shift in distribution of the woody species (Read et al. 1995). Low species composition. Forest microclimates, and therefore numbers of seedlings and saplings of a species in a forest *Corresponding author. Email: optripathi@yahoo.com ISSN 2151-3732 print/ISSN 2151-3740 online © 2010 Taylor & Francis DOI: 10.1080/21513732.2010.539987 http://www.infomaworld.com 158 O.P. Tripathi and R.S. Tripathi recruitment conditions, change after a disturbance. In gen- (<1 m high) and saplings (<15 cm DBH and >1 m high) eral, removal of the forest canopy results in more direct were studied by laying 30 quadrats of 2 m × 2min solar radiation, higher temperatures and reduced humidity. all three forest stands. The nomenclature for the species The primary reasons for forest destruction are cattle follows regional floras (Haridasan and Rao 1985–1987). grazing, over-exploitation for medicinal and ornamental Frequency, density, basal cover and importance value index plants and encroachment into forested area for cultiva- were calculated according to Misra (1968) and Mueller- tion. The objectives of the present study were to anal- Dombois and Ellenberg (1974). The Whitford index was yse and investigate soil characteristics, plant diversity, used to study the distribution patterns of species (Whitford community organisation and population structure of sub- 1948). Various diversity indices were calculated following tropical evergreen, semi-evergreen and pine forests of Magurran (1988). Population structure of forest stands was Meghalaya. studied at community level following Khan et al. (1987). The intensity of disturbance was calculated based on the number of cut stumps divided by the total number of stems of all tree species including cut stumps. Study area The study was conducted in three selected forests to characterise their floristic composition and population structure. Representative forest stands, that is, subtropi- Results ◦  ◦ cal evergreen (25 27 N, 90 19 E, 1425 m a.s.l.), semi- Soil characteristics ◦  ◦ evergreen (25 14 N, 91 43 E, 1475 m a.s.l.) and pine Pine forest occurs on well-drained, porous acidic soil with ◦  ◦ (25 32 N, 91 53 E, 1900 m a.s.l.) were selected in each a low nutrient concentration. Soils of pine forest were more forest. Soil samples were collected randomly from two acidic and had relatively low organic carbon, organic mat- (0–10 cm and 10–20 cm) depths at ten places on an annual ter, nitrogen and available phosphorus than the evergreen basis from the selected forest stands and were mixed thor- and semi-evergreen forests. Concentrations of all these oughly to obtain a composite sample. These samples were constituents were higher in the upper (0–10 cm) than the used to determine the pH, soil organic carbon, nitrogen lower (10–20 cm) soil layer in all the three forest stands and available phosphorus using the methods given in Allen (Table 1). et al. (1974) and Anderson and Ingram (1993). The state has a monsoon climate. The climatic vari- ables like temperature, rainfall and humidity vary widely from place to place due to the wide variation in topo- Plant diversity and stratification graphy. Based on atmospheric conditions, the year may Tree species richness was higher in broadleaf than in be divided into summer (March end to mid-May), rainy needle-leaf forests. A total of 76, 77 and 26 tree species (mid-May to September), autumn (October and November) were recorded in a 1-ha sampled area in evergreen, semi- and winter (December to February). The annual rainfall evergreen and a 0.3-ha area in pine forest, respectively. The varies widely, from about 1600 mm (Umiam, Ribhoi) to number of shrub species was higher in the semi-evergreen over 11,463 mm (Mawsynram, East Khasi Hills). The mean forest, and there were more herbaceous species in pine ◦ ◦ minimum and maximum temperature are 5 C and 33 C forest than evergreen forest (Table 2). and relative humidity is 56–92%. Stratification was distinct in the evergreen and semi- evergreen forests, with trees distributed in three distinct strata: canopy (>15 m), sub-canopy (8–15 m) and treelet Methods (2–8 m) layers. However, there was no clear stratification Twenty-five quadrats of 20 m × 20 m were randomly laid in in the pine forest. The canopy layer contained 13 species in the evergreen and semi-evergreen forests and 30 quadrats both evergreen and semi-evergreen forests, but was almost of 10 m× 10 m were laid in the pine forest, and all indi- exclusively composed of Pinus kesiya in the pine forest; viduals (>15 cm DBH) were recorded. Tree seedlings however, a few broadleaf trees, for example, Quercus sp., Table 1. Soil characteristics of subtropical evergreen, semi-evergreen and pine forests. Evergreen Semi-evergreen Pine Soil properties/Soil depth 0–10 cm 10–20 cm 0–10 cm 10–20 cm 0–10 cm 10–20 cm Soil moisture (%) 31.8 32.3 34.1 37.2 26.3 30.1 pH 5.80 5.41 5.3 5.1 5.12 5.10 Soil organic carbon (%) 2.62 1.84 2.18 1.64 2.38 1.60 Soil organic matter (%) 4.52 3.17 3.76 2.83 4.10 2.76 Total nitrogen (%) 0.42 0.35 0.27 0.19 0.17 0.14 −1 Phosphorus (µgg ) 28.7 25 31.7 24.5 17.2 15.1 International Journal of Biodiversity Science, Ecosystem Services & Management 159 Table 2. Community characteristics of the forests of and Helicia excelsa in evergreen forest, Psychotria errat- Meghalaya. ica, Symplocos paniculata, Adenia trilobata, Rhus javan- ica and Achronychia pedunculata in the semi-evergreen Evergreen Semi-evergreen Pine forest and Eupatorium adenophorum, Osbeckia crinita, forest forest forest Thysaenolaena agrostis and Rubus sp. in the pine forest Tree species (>15 cm DBH) (Tripathi 2002). Sample area (ha) 1 1 0.3 The tree seedlings, annual and perennial flowering −1 Density ha 1023 838 1050 plants and ferns constituted the ground layer in the forests. Basal cover 33.3 49.5 37.4 2 −1 The ground vegetation was more (57 species) species (m ha ) Species richness 76 77 26 rich in the pine forest than in the evergreen (44 species) Number of genera 58 56 23 and semi-evergreen (47 species) forests (Table 2). Among Number of families 35 34 17 the most common ground vegetation was Colquhounia Shannon diversity 4.2 4.21 2.19 coccinea, Hypericum laxum, Senecio cappa, Gleichenia index Simpson 0.02 0.02 0.06 sp. and Asplenium sp. in the evergreen forest, Anotis dominance index oxyphylla, Hemiphragma heterophyllum, Davaellia sp., Disturbance index 921 35 Crysopogon aciculatus and Asplenium sp. in the semi- (10%) evergreen forest and Asplenium sp. and Davaellia sp. in Shrub species (5 to <15 cm DBH, >1 m high) −1 the pine forest (Tripathi 2002). Density ha 1747 1608 1953 Species richness 20 23 21 Number of genera 18 20 18 Number of families 13 13 14 Dominance and distribution pattern Shannon diversity 2.77 2.91 2.39 index Life-form spectra showed a preponderance of phanero- Simpson 0.07 0.05 0.12 phytes in broadleaf forests, followed by chamaephytes and dominance index therophytes; pine forests had few phanerophytes (28.4%) Herbaceous species (<1 m high) 2 (Tripathi 2002). The dominance–distribution pattern was Density (100 m ) 1554 2976 1354 similar in evergreen and semi-evergreen forest, with a log Species richness 44 47 57 Number of genera 38 40 49 normal distribution pattern, signifying high equality and Number of families 32 25 28 low species dominance in the community. However, the Shannon diversity 3.40 3.55 3.53 pattern was a broken-stick shape in the pine forest, indi- index cating low equality in the dispersion of dominance of tree Simpson 0.05 0.03 0.04 species (Figure 1). The Shannon diversity index was higher dominance index in the broadleaf forest (4.2) than the pine forest (2.19), Number of tree stumps Note: Disturbance index = × 100. Total number of trees including tree stumps while the Simpson dominance index showed an opposite trend. The diversity index for the shrub and herbaceous Schima wallichii, Myrica esculenta and Exbucklandia pop- layers showed a similar trend to that for woody species ulnea, were found scattered in this forest (Tripathi 2002). richness (Table 2). The under-canopy (2–15 m) was poor in the pine forest, Most (68–95%) plant species in the forest had a but was the most species rich layer in the evergreen and contagious/clumped distribution pattern (Table 3), with semi-evergreen forests, contributing about 80% of total only a few species having regular or random distribution. of species richness. Elaeocarpus rugosus, Castanopsis tribu- the higher contagious distribution revealed that the species loides, Engelhardtia spicata and Duabanga grandiflora in were in patches, and was further supported by the fre- the evergreen forest, Aporusa oblonga, Dysoxylum binec- quency distribution pattern, with most species having a low tiferum, S. wallichii and Ficus sp. in the semi-evergreen frequency. forest were among the most dominant canopy trees. Lauraceae was the most common family, with 11, 10 and five species in the evergreen, semi-evergreen and pine Stand density and basal cover forest, respectively. Euphorbiaceae and Pinaceae were co- dominant in the broadleaf and pine forests. There were Stand density of tree species was higher in the ever- many families represented by a single species in all three green and pine forests (1023 and 1050 individuals per ha) forests. Dominance–distribution curves of the families than in the semi-evergreen forest (838 individuals per ha). showed that only a few families were dominant in broad- Although stand density of semi-evergreen forest was less and needle-leaf forests and large number of families had than the other two forests, the contribution to basal cover low FIV (Tripathi 2002). was higher (Table 1). The stand density in different girth Shrub species were represented by 20, 23 and 21 classes revealed that young individuals (<55 cm DBH) species belonging to 18, 20 and 18 genera and 13, 13 were most common (70% and 78%) and thereafter showed and 14 families in the evergreen, semi-evergreen and a declining trend (reverse J-shaped curves) in broadleaf pine forests, respectively (Table 2). The most common forest. Adult individuals (>95 cm DBH) were represented shrub species were Bridelia retusa, Callicarpa rubella by a few individuals in the broadleaf forest and completely 160 O.P. Tripathi and R.S. Tripathi (a) Evergreen forest Semi-evergreen forest Evergreen forest Pine forest Semi-evergreen forest Pine forest 100 400 (b) 0.1 0 1020 3040 5060 7080 90 Plant species Figure 1. Dominance–distribution of tree species in the subtrop- ical evergreen, semi-evergreen and pine forests. absent from the pine forest. However, in pine forest mature trees (55–95 cm DBH) contributed most to stand density. 15−35 35−55 55−75 75−95 >95 The distribution of basal cover was opposite to that of stand Girth-class (cm) density, that is, mature and adult trees, although less in Figure 2. Density–distribution (a) and basal cover (b) distri- number, contribute most to the basal cover (Figure 2). bution in the subtropical evergreen, semi-evergreen and pine forests. Population structure Mean seedling density (plants 100 m ) was 494, 1341 Glochidion acuminatum, Garcinia pedunculata and Persea and 501 in the evergreen, semi-evergreen and pine duthiei in semi-evergreen forest and Myrica esculenta, forest, respectively. The most common seedlings were Quercus glauca, Lindera leata and Litsea sp. in the pine Ostodes paniculata, Persea duthiei, Macaranga den- forest (Tripathi 2002). ticulata and Engelhardtia spicata in evergreen forest, The mean density of adult trees was 1023, 838 and −1 Cinnamomum tamala, Aporusa oblonga, Celtis tetranda, 1050 individuals ha in the evergreen, semi-evergreen Callicarpa arborea and Ficus racemosa in semi-evergreen and pine forest, respectively. Based on density, all three forest and Eurya acuminata, Combretum acuminatum, forests showed a dominance of tree seedlings and low pop- Lyonia ovalifolia and Zanthoxylum alatum in pine for- ulation density of saplings and adult trees, resulting in an est (Tripathi 2002). The mean sapling density was upright pyramid-type structure. The preponderance of tree −1 −1 3813 stem ha in evergreen forest, 4056 stem ha in seedlings, followed by a steep decline in population den- −1 semi-evergreen forest and 2212 stem ha in pine for- sity of saplings and adult trees indicated that the seedling est. The most common saplings were C. tamala, Citrus to sapling stage was the most critical stage in the life of a medica, Glochidion assamicum and Callicarpa vestita tree, and most mortality (about 93%) occurred during this in evergreen forest, Camellia cauduca, Celtis tetranda, period (Figure 3). Table 3. Distribution pattern of trees, shrubs and herbaceous species in the subtropical broad- and needle-leaf forests. Evergreen forest Semi-evergreen forest Pine forest Distribution pattern Tree Shrub Herb Tree Shrub Herb Tree Shrub Herbs Regular 6(8) 0 6(14) 1(1) 1(4) 5(11) 1(3) 1(5) 5(9) Random 18(24) 1(5) 5(11) 15(20) 2(9) 9(19) 3(12) 4(19) 12(21) Contagious 52(68) 19(95) 33(75) 61(79) 20(87) 33(70) 22(85) 16(76) 40(70) Total 7620447723472621 57 Importance value index Density per hectare 2 −1 Basal cover (m ha ) International Journal of Biodiversity Science, Ecosystem Services & Management 161 a few deciduous species, which shed their leaves dur- Evergreen forest Semi-evergreen forest ing the dry months between February and April, gives a Pine forest semi-evergreen appearance to the forest. The majority of species showed a contagious/clumped distribution in all the forests, which could be attributed to insufficient seed dispersal (Richards 1996), topography and soil factors (Currie 1991). A regular dispersion pattern, as observed in the present study, may be the consequence of direct competition for water and nutrients, allellopathy or frequent disturbance, which largely contribute to the main- tenance of a high level of diversity (Armesto et al. 1986). The change in dominance distribution pattern from log normal in the broadleaf to broken-stick shape in the pine forest indicate a marked shift from high equality to high dominance in the community due primarily to disturbance. The dominance of phanerophytes in broadleaf forests is indicative of a mild and moist climate, as also found by Archibold (1995). Dominance of therophytes followed by phanerophytes in pine forest suggest a transformation of Seedling Sapling Adult mesic habitat supporting broadleaf forests to a disturbed Age group xeric habitat that provides more favourable conditions for annuals and tolerant tree species like Pinus kesiya (Tripathi Figure 3. Overall population structure of the subtropical forests 2002). In general, the higher values for therophytes, the of Meghalaya. more homogenous are the stands (Singh et al. 2006). The girth class composition of stands at high distur- Discussion bance levels resembles a J-shaped distribution (number increases with increasing age), indicating future decline in The selected forest types are the major forest types in Meghalaya State; they cover an area of about 41% of the population. However, at low disturbance, the trend is the total geographical area of the state. These forests are reversed due to the presence of a large number of indi- between 800 and 2000 m a.s.l. The climate is seasonal, viduals in lower girth classes, an indicator of a growing with a 7–8-month rainy season. The evergreen and semi- population (Pandey and Shukla 2001). Selective thinning evergreen forests differ, depending on the species domi- of treelets for firewood and their death due to surface fire nance in the canopy. Evergreen forests are found where seems to be a major cause of loss of young individuals. rainfall is relatively high and soil moisture is favourable for The tree density in the broadleaf forest and its reverse most of the year. The areas with low rainfall support semi- J-shaped distribution in different girth classes could be evergreen vegetation, mainly due to the coarse texture or related to gap phase dynamics, tree regeneration behaviour high slope gradient or both (Tripathi 2002). Human inter- and age of the stand. In the pine forest, density distribu- vention in these broadleaf forests has paved the way for tion in different girth classes seems to be determined by the cumulative effect of natural thinning, selective cutting development of pine forests, which represent the edaphic and surface fires, as these factors cause heavy mortality and biotic climax community on disturbed sites, which are of tree seedlings and saplings. Variations in species rich- seasonally dry and nutrient poor. ness and diversity at a local scale are affected by a number The most noticeable features of the tropical and sub- of complex and interacting variables, including both natu- tropical humid forests are the species richness, hetero- ral environmental factors and human-made changes to the geneity and complex community organisation. Rainfall local environment. At relatively small spatial scales, envi- pattern and temperature regime strongly influence their ronmental variables, such as chemical and physical soil floristic composition, which is further modified by edaphic properties (Fu et al. 2004; Poulsen et al. 2006), topogra- and biotic influences (WCMC 1992). The dominance of phy (Fu et al. 2004; Cielo-Filho et al. 2007) and human families like Lauraceae, Euphorbiaceae, Moraceae and disturbance, such as logging (Brown and Gurevitch 2004) Rubiaceae in the broadleaf forests is similar to tropical rain forest of Pasoh reserve forests in Malaysia and subtropi- and livestock grazing (McEvoy et al. 2006; Dufour-Dror cal forests/sacred forests in Meghalaya (Manokaran et al. 2007) are important drivers of community structure. 1991; Mishra et al. 2004; Tripathi and Khongjee 2010; Tripathi et al. 2010). The soil profile in broadleaf forests is well developed, Conclusions acidic and rich in organic matter and nutrients. The soil in pine forests, however, is more acidic and low in organic All three forest types are found inter-mixed at higher ele- matter and nutrients. The subtropical evergreen forest is vations under similar climatic conditions. However, the richer in species than the evergreen forest. Presence of evergreen forest is mainly in more humid and inaccessible Density per 100 m 162 O.P. Tripathi and R.S. Tripathi areas. In this forest, the tree species richness is lower Condit R, Hubbel SP, LaFrankie JV, Sukumar R, Manokaran N, Foster RB, Ashton PS. 1996. Species–area and species– than in the semi-evergreen forest. Although all three for- individual relationships for tropical trees: a comparison of est types were exposed to different levels of disturbance, three 50-ha plots. J Ecol. 84:549–562. the pine forests on nutrient-poor and relatively dry soil Currie DJ. 1991. 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Journal

International Journal of Biodiversity Science, Ecosystem Services & Management – Taylor & Francis

Published: Dec 1, 2010

Keywords: broadleaf forest; dispersion pattern; diversity and dominance indices; needle-leaf forest; population structure; soil properties; stratification

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