Analysis of Edge Effects on Fragmented Forests Using Forest Inventories in Southwestern Amazonia

Abstract:

Deforestation fragments contiguous forests into smaller and smaller pieces, inducing ecological and biological changes in forest ecosystems. Edge effects are spatial and temporal phenomena. The effects of forest fragmentation vary primarily as functions of edge penetration distance, spatial arrangements and time of persistence of forest edges. Across varying penetration distances in a forest edge, numerous changes occur including elevated tree mortality and canopy desiccation, changes in forest structure and species composition, alternation of hydrological and carbon cycles. We analyzed the effects of edge penetration distance and time of persistence of forest edges on forest biophysical characteristics based upon more than thirty 500m transects over highly fragmented forests in Acre, the southwestern Amazon. Spatial variability of tree data (diameter at breast height – DBH, above ground biomass, tree density, species composition and population) was measured along a penetration distance of 500m from forest edges. Different edge age classes (1-5yr, 6-10yr, > 10yr) and edge penetration distances were identified based upon a Landsat time-series analysis. The number of individual plants with DBH > 10cm tends to be greater near edge (largest in the first 100m), while larger biomass amounts are found at > 300m distance. The impact of penetration distance on biomass, however, is not statistically significant. In terms of the distribution of DBHs, while smaller trees with DBH <=20cm account for 70% of all trees, larger DBH trees tend to increase after 300m penetration distance. The effect of edge persistence period (edge age) is not significant for both the number of individual plants as well as the biomass, however it is more pronounced on secondary species’ biomass such as Cecrcopia sp and bamboo, which increase as edges persist longer.