Environmental heterogeneity caused by anthropogenic disturbance drives forest structure and dynamics in Brazilian Atlantic Forest

We evaluated how tree community floristic composition, forest structure and dynamics varied over a period of 13 years across a topographic gradient of ravines created by anthropic disturbance in Brazilian Atlantic Forest. The study area is located within a fragment of Atlantic Forest (21° 09' S, 44° 54' W), in Minas Gerais state, Brazil. This work was based on data of tree diameter at 1.3 m from the soil, collected in four inventories. Each individual was recorded as being in one of three stratified topographic classes: hilltop, slope and bottom. We used direct gradient analysis to evaluate floristic compositional changes, phytosociological analysis to evaluate structural variations, and assessed demographic and biomass changes over time through analysis of rates of forest dynamics. The results did not reflect modifications in the patterns of floristic composition and species diversity along the topographic gradient, while differences in forest structural attributes and dynamics may be detected at these smaller spatial scales. Thus, the same species group may employ different strategies against different restrictive environmental factors. Finally, we suggest that floristic composition and species diversity may be less sensitive parameters for post-disturbance responses than forest dynamics and structure

Unseen rare tree species in southeast Brazilian forests:a species abundance distribution approach

Rarity is an important aspect of biodiversity often neglected in ecological studies. Species abundance distributions (SADs) are useful tools to describe patterns of commonness–rarity in ecological communities. Most studies assume field observations of species relative abundances are approximately equal to their true relative abundances, thus dismissing the potential for, and importance of unseen rare species. Here, we adopted the approach proposed by Chao et al. (Ecol, 96:1189–1201, 2015) to estimate the number and abundance of unseen species, and thus the true SADs, for tree species in 48 forest sites in Minas Gerais state, Brazil (4 rainforests, 35 semideciduous forests, and 9 deciduous forests). Also, we assessed the correlations between both unseen and rare species and sampling protocol and environment characteristics (climate, terrain, terrain heterogeneity). We found estimated true SADs invariably had higher species richness values than observed in the surveys, due to the increase in rare species. We estimate that up to 55.6% of tree species per site were unseen (8.5–55.6%), with an average of 26.6%. The estimated percentage of rare species per site was between 31.9% and 72.8%, with an average of 57.78%. We found rarity to be most strongly correlated with the percentage of unidentified trees, local terrain conditions and heterogeneity at site-level. Semideciduous forest and rainforest had similar higher percentages of unseen species (c. 27.2%) when compared to deciduous forests, probably due to the relatively higher local heterogeneity of these forests, which may provide more niches for rare species. Future studies should consider estimating true species abundances to better assess biodiversity. © 2020, Akadémiai Kiadó Zrt