DEVELOPMENT OF FLORISTIC DIVERSITY IN 10-YEAR-OLD RESTORATION FORESTSON A BAUXITE MINED SITE IN AMAZONIA

Patterns of plant and animal diversity were studied in a 10-year-old n ative species reforestation area at a bauxite-mined site at Porto Trom betas in western Para State, Brazil. Understorey and overstorey floris tic composition and structure, understorey light conditions, forest fl oor development and soil properties were evaluated in a total of 3878. 5-m(2) plots located in the reforestation area at varying distances up to 640 m from the boundary with the surrounding primary forest. Wildl ife surveys focusing primarily on birds and bats were also conducted t o assess the role of seed-dispersing animals in regeneration of woody forest species within the plantations and colonization by primary fore st species not included in the original reforestation. Regeneration de nsity, species richness and species diversity (Shannon-Wiener index) f or woody perennial species, vines, herbs and grasses were strongly cor related with the diversity of planted tree species and structural deve lopment parameters, degree of forest floor development and soil pH. Th e better developed closed-canopy plots (>40% crown closure) were chara cterized by relatively well-developed litter (O1) and humus (O2) layer s, more acidic soils being typical of the surrounding primary forests, and a more diverse herb, vine and woody perennial flora with a greate r representation of primary forest species being characteristic of lat e secondary forests. In closed-canopy plots' a total of 125 tree, palm and shrub species were censused (versus 34 in the more open-canopy pl ots), of which 75 species are known to have been introduced by natural means from the surrounding primary forest (versus 11 species in the o pen-canopy plots). Among the plantation plots, there was significant c olonization by primary forest woody species up to 640 m away from the primary forest edge, although both the abundance and the diversity of colonizing species declined with increasing distance into the plantati ons. Smaller-seeded primary forest woody species dispersed by mammals and birds represented a higher proportion of the colonizing species co mpared with the larger-seeded species. These data are consistent with the results of the wildlife surveys, which indicated that most animal seed dispersal is provided by bats, that the most common frugivorous b at and bird species in the plantations feed on small-seeded plant spec ies and that birds and mammals that typically disperse larger-seeded t ree species (such as toucans, trogons, tapirs, deer and primates) are still rare in the reforestation area. These results suggest that while the reforestation program has been successful in creating a favorable environment for regeneration of a native primary forest species, furt her management interventions, such as enrichment plantings, may be req uired to accelerate regeneration of large-seeded primary forest specie s. (C) 1997 Elsevier Science B.V.