PLANT DIVERSITY AND STRUCTURAL-ANALYSIS OF A TROPICAL DRY FOREST IN SOUTHWESTERN MADAGASCAR

For this paper, we sampled a fenced and an unprotected portion of a dry gallery forest (the Beza Mahafaly Reserve) in southwestern Madagascar for structure and floristic composition. Seedling plots were also sampled to assess invasion and regeneration. A total of 923 plants greater-than-or-equal-to 2.5 cm diameter at breast height (DBH) were censused in 25 transects. Sixty-nine species and 43 genera were represented. In plant density, diversity, and size classes of individuals, the forest is similar to many continental tropical dry forests in Africa and the Neotropics. Over 80 percent of those species identified were native, as were 26 percent of the genera. Unlike many insular forests, Beza Mahafaly is not being invaded by fast-growing exotic species. There were no noticable differences in density, diversity, size classes, or proportion of native species between transects within and outside of the protected reserve. Two distinct microhabitats were noticed. Individual plants were more dense on ''drier'' soils; whereas, large trees greater-than-or-equal-to 25 cm DBH were over twice as frequent on ''wetter'' soils. The floristic composition also differed, with only two species of tree, Tamarindus indica and Azima tetracantha, being common to both habitats. The distribution and density of lemur populations within the forest appear to be directly related to microhabitat differences.