Trajetórias populacionais de espécies arbóreas sob efeito de fragmentação florestal na Amazônia Central

Abstract

This study had the objective of evaluating how the relative density of conspecifics could affect the demographic parameters of the populations of 55 canopy and sub-canopy tree species in the context of forest fragmentation in Central Amazon. The studied demographic parameters were recruitment, mortality and intrinsic growth (λ) as response variables, and initial density (no of individuals/ha) as explanatory variable. The database of the long-term experiment Biological Dynamics of Forest Fragments Project (PDBFF) was used. At the study area, 66 plots of 1 ha were arranged in the different fragments sizes (1 ha, 10, ha and 100 ha) and continuous forest (control) in which all trees with DBH ≥ 10 cm have been monitored from 1980 to 2009. In the first study, the effect of forest fragment size over the demographic parameters of recruitment and mortality were evaluated, as well as how these parameters varied in relation to the different tree species. Recruitment increased significantly in the fragments of 100 ha and for six species of the Chrysobalanaceae family and two of the Humiriaceae family. Mortality was not significantly affected, in general, however, a few species suffered higher mortality: five species of the Chrysobalanaceae family and one of the Caryocaraceae family. In the second study, the effects of forest fragment size and initial density over the intrinsic population growth of the species, and the effect of the fragment and presence of forest edge over the individual growth of each species in relation to the control (continuous forest and forest interior) were evaluated. Based on the data from tree monitoring, the chances of change in the populations or in growth were tested according to initial density undergoing effect from fragment size and edge effect. The initially less dense populations presented less chance of change and higher chance of growth. An initial density limit of 10 individuals/ha was identified. Below this limit, the differences between fragment size and presence of edge were significant for the chances of population change, and, above it, there were no differences between the areas. Among the 55 analyzed species, only 10 were significantly affected in intrinsic population growth and size of fragment or edge. Of these, only two species had positive growth over the 29 years: Rinorea racemosa and Licania blackii, both common and high density population species. In conclusion, the initial conditions of local density were fundamental for defining the population trajectories of these tree species, that fragment size and edge distance negatively affect the populations and that mortality dependent on the density of conspecifics operates independent from fragment size.