The highly biodiverse Atlantic Forest has been heavily exploited and its remnant areas, which are mostly composed of secondary forests, cover less than 20% of its original extension. This study analyzed the structure, aboveground biomass (AGB) and species diversity of a secondary evergreen rainforest in the state of Santa Catarina, southern Brazil. Individuals with diameter at breast height ≥ 5 cm on 22 sample plots were measured, totalizing 3.49 hectares of sampled area. A mean AGB of 201.6 Mg ha -1 (standard deviation = 35.5) was found; Hyeronima alchorneoides and Miconia cinnamomifolia represented 29.1% and 7.6% of the community AGB ha -1 , respectively. A total of 153 species distributed in 107 genera and 55 families was observed; it was estimated that 121 species (95% confidence interval: [117, 125]) occurred in one hectare. These results highlight the importance of secondary forests for biodiversity restoration/conservation and carbon sequestration.

Tropical and subtropical regions shelter high levels of biodiversity. A combination of biological, environmental and anthropogenic factors influences tree community diversity and composition. Here, we use data from the IFFSC project to test the effect of conspecific and heterospecific density dependence, canopy cover and distance to edge on saplings populations of 229 woody species in 159 plots distributed across three forest types in Southern Brazil. All plots were measured twice with a standardized time interval of 5 years. We fitted one ordinary least square regression model to each species to test the strength of each predictor on the species' population growth rate, and one global mixed effect model including forest type, ecological group and the interaction between distance to edge and conspecific density to test their impact in the overall trend of the species. Our analysis provided circumstantial evidence that conspecific density dependence is shaping diversity of forest fragments. This mechanism was present for 75.5% of the species, while heterospecific density affected 10% of the species. Canopy cover affected the population dynamics of 9.2% of the species and distance to edge affected 7.4% of the species. Forest type had a significant effect in the global model, suggesting that population dynamics differ between different forest formations. Ecological group was not significant in the global model suggesting that the mechanism affects species similarly despite their ecological group. The interaction between distance to edge and conspecific density was significant in the global model, suggesting that this mechanism differs between interior and edge of fragments. This work represents one of the few large-scale analyses of conspecific density dependence in fragmented secondary forests. Our results show that, once the forest is stablished, conspecific density dependence is crucial in sapling population dynamics, despite high levels of fragmentation.

Studies on the dynamics of managed forests are essential for planning and executing management strategies. Timber harvesting can modify recruitment rates, mortality, gain and loss of basal area of the remaining stand. In secondary forests, especially in the Atlantic Forest, these studies are still scarce. Our study hypothesis is that the management intervention stimulates the growth of the remaining trees, overcoming the reduction of the growth of the damaged trees and the harvest mortality. We investigated the dynamics of the remaining trees and recruits (in number of individuals and basal area), with DBH ≥ 5 cm, by ecological group of the species, and the damage to the remaining adult individuals. We measured eleven permanent plots with 1.600m² each, before and four years after being harvested in a secondary forest in southern Brazil. We found that the different harvesting intensities significantly influence the forest dynamics, special the annual recruitment rates, while basal area gain/loss showed a weaker relationship to logging intensity. However, the mortality rates are similar in control plots and managed plots. We also observed that in the managed plots, the recruitment rate (5.3 ± 1.9% year-¹) exceeded mortality (2.3 ± 1.2% year-¹). Among ecological groups, we found less recruitment of climax species than of secondary species. In general, the proportion of damage of remaining trees decreased over time. We conclude that the management has modified the forest dynamics, indicating that planning, including adequate cutting limits and low impact harvesting methods are essential for achieving the sustainability of forest management.