Abstract
Forest fragments present shapes and sizes that become them more or less susceptible to external factors, which can be measured by means of ecological indexes. The aim of this research was to diagnose conservation status and to quantify forest fragments in part of the Brazilian Atlantic Forest. Forest fragments were mapped and landscape ecology metrics were calculated, including area size, fractal dimension index, and edge index. These three metrics were modeled using the Weibull-3P probabilistic function in order to quantify fragments in a specified range. A bivariate function also was applied relating the indexes with fragment area size. The diagnosis revealed that the study area is highly fragmented, since the forested area covers only 13.7% of the total area. About 89% of the forest fragments have area from 10 to 100 ha, whereas fragments larger than 100 ha totalize about 11%. The metrics allowed discriminating the forest fragments by their conservation status. This study suggests that smaller fragments should be managed as stepping stones to the larger ones. As conclusion, larger forest fragments present more complex shapes and high edge effect. Thus, smaller forest fragments present variability of shapes from simple up to the more complex ones, besides edge effect much more variable than the larger fragments. The frequency of fragments in relation to the studied variables follows a normal. This means that well-conserved forest fragments, that is, with biggest areas, lower edge effects, and more rounded shape, are the scantiest ones. Key words: Forest area size, edge index, fractal dimension index, probability density function.
Highlights
The human pressure on forests in Brazil has occurred since the beginning of its colonization
Forest fragmentation can be defined as any area of natural vegetation interrupted by human barriers such as roads and crops, or natural barriers such as rivers and lakes, which can reduce the flow of animals, pollens and seeds (Forman and Godron, 1981)
The aim of this study was: (1) to present a diagnosis of conservation status of forest fragments using as criteria landscape ecology metrics and (2) to generate probabilistic models to quantify forest fragments
Summary
The human pressure on forests in Brazil has occurred since the beginning of its colonization. The forest fragmentation consists of a mosaic of patches contained in a matrix, in which its structure suffers external influences such as wind, fire, and human intervention. In this sense, ecological metrics are used to relate perimeter and area, reflecting the level of complexity and edge of patches. Considering the assumption that the circle is the geometric shape with a smaller perimeter for a certain area, the most rounded forest fragment has the lower edge effect, besides its shape is less complex (Broadbent et al, 2008; Couto, 2004; Forman and Godron, 1981)
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