EDGE EFFECTS IN CENTRAL AMAZONIAN FOREST FRAGMENTS

Current descriptive models of edge effects describe little more than t he relationship between perimeter and area. A more realistic model, on e that incorporates the additive nature of edge effects, is presented and tested. The total edge effect at a location within a patch is mode lled as the sum of edge effects at points along the edges of the patch , weighted by the distances from the edge points to the location. At f our sites in the central Amazon approximate to 80 km north of Manaus, Brazil, I measured vertical stratification of foliage in three primary forest habitats: (1) continuous forest close to linear edges, (2) 10- ha forest fragments, and (3) 1-ha forest fragments. Foliage thickness (foliage density along a vertical line) was scored in six height inter vals (0-2, 2-5, 5-10, 10-20, 20-30, and 30-40 m). With decreasing dist ance from a linear edge, understory (0-5 m) foliage thickness increase d and overstory (10-30 m) foliage thickness decreased, and the relatio nship between foliage thickness and distance to the edge agreed with t hat predicted by the model. Using parameter estimates obtained from th e ''best fit'' of the model to these data from linear edges, understor y and overstory thickness in 1- and 10-ha fragments was predicted. Fol iage thickness varied extensively among fragments, but agreed quite cl osely with that predicted by the model, and the additive model perform ed better than a curvilinear non-additive one.