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O papel relativo da configuração da paisagem, fatores naturais e manejo da terra na estrutura e diversidade de florestas secundárias no leste da Amazônia
(Universidade Federal do Pará, 2016-04-29) LIZON ROMANO, Leon Pastor; FERREIRA, Joice Nunes; http://lattes.cnpq.br/1679725851734904
Secondary forests cover about 23% of deforested areas of the Brazilian Amazon. Although they have clear differences with primary forests, forests in succession have undeniably ecological, social and economic importance. The eastern region of the Amazon, specifically the area known as arc of deforestation, presents a fragmented landscape, characterized by several land uses and large extent of secondary forests. This study aimed to evaluate the relative role of landscape variables, natural variables and use and soil management on the structure and floristic diversity of secondary forests in the southeast of Pará. We surveyed 20 secondary forests along an age gradient from 5 to 20 years. In each fragment, were established: i) transects of 10 x 250m (0.25 ha) to study the plants with diameter at breast height (DBH) ≥ 10cm (DBH ≥10cm) in plots of 10 x 10m (total 25 ) ii) 5 subplots of 5 x 20m nested within the transects to study the plants (DBH) <10cm and ≥2cm. (DBH <10cm). Structural variables were measured (plant density, height, basal area, number of stems) and species diversity variables (richness, and Shannon and Simpson diversity index) considering trees, palm trees and lianas. A set of landscape configuration variables for each fragment were considered (eg. Size, perimeter, distance and proportion of primary forest and total forest in a radius of 500 m, 1 km and 3 km); natural variables (altitude and slope) and the historical use of each transect: land use intensity index (LUI) and number of agricultural cycles. The history of land use was assessed by a combination of satellite images time series and interviews with landowners. We undertook analyses with RandomForest package in the R software environment. Structural and diversity parameters had great variation among the 20 secondary forests studied. Variables such as height and basal area have not grown consistently over the age gradient. The percentage of variation of the response variable explained by the models ranged from 0 to 38.75%. In general, all categories of variables (age, landscape, natural factors, land management) contributed to explain the variation in the data, but the landscape variables were those that contributed the most (20.44 to 66.92%) . Age was not the most important factor to explain structural parameters except the liana density (54.17%) which reduced in forests from 15 years. In contrast, age was a major factor explaining the diversity of species of plants DAP≥10cm (Simpson index). Along with the lanscape, age explained the total variation in diversity (57.60% and 42.49, respectively). The land use management variables were important to explain the basal area of the individuals DAP≥10cm and DBH <10cm (25.22% and 36.19%, respectively). All landscape variables investigated helped to explain the structural parameters and diversity, most explaining over 50% of the variation. The area, perimeter and perimeter-area ratio of the fragments best explained the structural parameters and species richness. On the other hand, the diversity of Simpson was mainly explained by the cover of primary forest; distance to the primary forest (1 km) and distance to forests (primary and secondary). The natural variables (slope and altitude), as well as the municipality, which includes natural variations between sites were more important in explaining the variation in density and basal area in DBH <10cm plants. Overall, while a combination of prior land use, landscape and natural environmental changes were important for the regeneration of the structure of forests, coverage of primary forests and the distance remaining forests (primary and secondary) were important to the initial recovery in species diversity. The patterns reported in the present study are important to understanding the drivers of regeneration and for informing decisions regarding restoration strategies in this most deforested region of the Brazilian Amazon.