ESTRUTURA E DEMOGRAFIA DE FLORESTAS SECUNDÁRIAS TROPICAIS NO SUL DO BRASIL: EFEITOS DO ESPAÇO, DO TEMPO E DO AMBIENTE (Tese de doutorado)

Analysis of the structure, diversity and demographic dynamics of tree assemblages in tropical forests are especially important to evaluate successional trajectories locally and the diversity of regional successional trajectories. We conducted a long-term study to investigate how the structure, species richness and diversity of secondary tropical forests changes over time. Trees (DBH ≥ 5 cm) in the Atlantic Forest of southern Brazil were sampled twice in 10-year period (2007 and 2017), in six stands (1 ha each) that varied in age from their last disturbance (25, 60, 75, 90, and more than 100 years). We compared forest structure (abundance, and basal area), species richness, alpha diversity, demographic rates (mortality, recruitment, and loss or gain in basal area), species composition (by non-metric multidimensional scaling – nMDS), spatial beta diversity and temporal beta diversity (based on β Sørensen, turnover (βsim) and nestedness (βsne) indices) among stand ages and study years. Demographic rates recorded to 10-year interval indicate a rapid and dynamic process of species substitution and structural changes and are less predictable in younger stands than in older stands. Structural recovery occurred at a faster rate than beta diversity and species composition. The successional gradient evidenced a pattern of species trade-off over time, with less spatial dissimilarity and faster demographic rates in younger stands. As stands grow older stands show larger spatial turnover of species than younger stands making them more stochastic in relation to species composition. Stands appear to split chronologically to some extent, but not across a straightforward linear axis, reflecting stochastic changes, evidence for nonequilibrium community. The total spatial and temporal dissimilarity of the assemblies was driven mainly by the substitution of species. This indicates that the disturbances resulted in significant changes in the composition of species that are becoming more heterogeneous. These results reiterate the complexity and variability of forest succession and serve as a reference for the evaluation and monitoring of local management actions and for defining regional strategies that take into account a diversity of local successional trajectories including to evaluate the effectiveness of restoration measures in secondary forests of the Atlantic Forest biome.