Conseqüências ecológicas da fragmentação florestal na Amazônia

Abstract

Many studies have analyzed the ecological consequences of forest fragmentation on Amazonian forests and the results of these studies are summarized here. Habitat fragmentation has extensive effects on Amazon rainforests, affecting diversity and community composition in the resulting fragments, and also affecting ecological processes like pollination, nutrient cycling, and carbon fixation. The ecological changes resulting from fragmentation are generally of inverse proportional magnitude to the size of the fragment area. Consequently, smaller fragments are usually less species-rich and have fewer species per area than do larger forest fragments. Forest fragments in the Amazon seem to be particularly prone to edge effects. Fragmentation dramatically increases edges of tropical forests: new edges are artificial and abrupt, forming a stark boundary between the forest and the surrounding, altered landscape. One of the most striking effects is a dramatic increase in the mortality of trees, leading to increased canopy-gap formation. Edge effects in the fragments also alter physical gradients and species abundances. In general, species that are most vulnerable to fragmentation tend to respond negatively to edges, have large area requirements, and/or are intolerant to the surrounding “matrix” (i.e. the mosaic of modified habitats around the fragments), whereas species that are resilient to fragmentation usually have an opposite set of characteristics.