Aspectos ecológicos para categorização de estágios sucessionais na Floresta Atlântica

Abstract

The Atlantic Forest is one of the richest Brazilian biomes in biodiversity, and is also the one that has suffered most from anthropogenic activities, which has led to a fragmentation of its remnants that are in different stages of succession. Thus, the study aimed to describe the floristic, environmental and structural composition of the arboreal and regenerating stratum of three different remnants of Dense Ombrophylous Lowland Forest, in the north of the state of Espírito Santo, and relate them to different classifications and norms of successional stages of the Atlantic Forest. For the arboreal vegetation, 15 30m x 30m plots were allocated, with 5 plots within each fragment. All living arboreal individuals with diameter at breast height (DBH at 1.30m) ≥ 5 cm were sampled. For regenerating vegetation, sampling was carried out in the area of existing plots in the tree stratum. We established 15 sampling units, in which each unit was composed of 3 subplots with dimensions of 5 x 5m, with 5 sampling units demarcated in each of the three fragments. The criteria were minimum height of 50cm and diameter at breast height (DBH) < 5. Phytosociological parameters, Shannon index and equability were obtained for both strata to compare the structure and floristic composition between the fragments. An indicator species analysis (ISA) to verify indicator species, a similarity between the sampling units of the fragments, based on Jaccard's index and using the (UPGMA) method, and an NMDS to verify clusters. To evaluate the relationship of the vegetation of the two strata with the environmental variables, data on luminosity and soil attributes were obtained, the luminosity was obtained from hemispherical digital photographs, which were collected and analyzed by GLAMA software. The soil was collected from 0 - 20 cm, and in each plot 5 samples were collected and later homogenized. With the environmental variables, Redundancy Analysis (RDA) was performed to verify the influence of the variables on the vegetation of both strata. Fragments 1 and 2 showed lower species richness and diversity in detriment of fragment 3 in both strata, also showed a predominance of initial secondary species, a greater relationship with light and a soil poorer in nutrients, suggesting that the fragment is in a stage of medium secondary vegetation. Fragment 3 showed a predominance of late-secondary species, higher soil fertility, and a lower relationship with light, which may indicate conditions of an advanced vegetation fragment. The analyses showed that the environmental variables influenced the vegetation of the two strata and these changes cause differences in structure and composition, which can cause different successional trajectories. Regeneration also contributed to the classification of successional stages, and is important to predict the recovery and the consequent successional advance of the forest. With this study, we can see that a larger number of parameters makes the classification of successional categories more efficient. This is because other ecological indicators help to better understand the successional trajectory and not only structural parameters.