Abstract

This study documents the community composition and forest structure of lowland rainforest in eastern Madagascar, with a first quantitative description of the primary lowland rainforest of Reserve Naturelle Intégrale de (RNI) Betampona. An intensive field survey of vegetation and environmental factors was conducted over two consecutive field campaigns in RNI Betampona, an isolated primary forest reserve located ca. 40 km northwest of the city of Toamasina. One hundred 10 m-diameter vegetation survey plots were inventoried and re-measured in 2004 and 2005. Two hundred forty-four tree species belonging to 49 families comprised the 2,487 stems greater than or equal to 5cm diameter at breast height (DBH) measured in 2004, with an average of 19.27 species per plot (2,227 and 15.71 respectively in 2005). Stem density per plot ranged from 12 to 52 for trees ≥5cm-DBH in 2004 (12 to 38 in 2005), while regeneration stems less than 5cm-DBH had a per-plot average of 57.28 in 2005 (range 19 to 140) and 94.19 (range 22 to 224) per hectare in 2004. The substantial decrease in ≥5cm-DBH trees and in stems ≥5cm-DBH from 2004 to 2005 suggests a forest undergoing thinning, perhaps following recovery from gap formation. Importance Value Indices (IVI) calculated for tree species indicated that an unidentified Uapaca species, Ravenala madagascariensis, Anthostema madagascariensis, Canarium spp and Cassipourea lanceolata were the most important species according to their overall frequency, dominance and abundance values, and accounted for 10% of the overall IVI.