Edge effects on the regeneration of forest fragments in south Brazil.

摘要

This work addresses three main questions: (1) Do different types of species occur at different distances from the edge in the tropics? (2) Are non-monotonic patterns of plant density common in edges? (3) If so, which mechanism is generating it, and how do fragment size and edge orientation affects non-monotonic patterns?;I established 48 transects 4 m wide, 25-100m long. I identified 192 species, on a sample of 16,674 saplings higher than 1m, and smaller than 5 cm DBH. Transects were located in 19 forest fragments, ranging from 0.4 ha to 650 ha. Two additional data sets were used. Fourteen transects, 10 m wide, 45-100m long, were surveyed for density of trees (above 10cm DBH), and fifty-five transects 50m or 100m long were surveyed for light and temperature measurements. The study site is located in North Parana, Brasil.;The occurrence of pioneers and canopy species closer to edges than the average individual, indicates that the light enhancement at these sites, is selecting species adapted to this condition. Furthermore, where light penetrates further into the forest, (north edges), the species composition of sites deeper into the forest, resembles the species composition of sites closer to the edge of protected (south) edges.;Sapling density showed to have a non-monotonic pattern. It is associated with species composition when all transects are pooled, and when different transect subsets are considered. The association sapling density/species composition ceases to exist around 35 m from the edge, in all different groups considered.;Sapling density is related to lateral light on the edge, but trees control light deeper on. The point at which one condition switches to the other, coincides with the point at which Vapor Pressure Deficit stabilizes (35m). Further evidence that the edge is 35 m wide, is that plant diversity peaks at 35 m. Species composition on the seven subsets (large-small, north-south, and three sizes of saplings) confirm that species composition is related to distance from the edge up to around 35 meters. After that, no pattern is shown.;Species composition of whole transects in small fragments somewhat resemble the species composition found in edges in this region. The diameter of small fragments is many times smaller than 200 m, so that entire transects in small fragments are closer than 100 m to a secondary edge. In those cases, a weak secondary edge effect is added to the entire transect, amplifying the edge effect. (Abstract shortened by UMI.).