Density dependence in two understory tree species in a neotropical forest

Abstract

Density dependence was examined in two species of neotropical treelets, Faramea occidentalis and Desmopsis panamensis, in a 50-ha plot on Barro Colorado Island in Panama. Survival and growth probability of plants larger than 1 cm dbh (diameter at breast height), and recruitment into the 1-cm class, were assessed as a function of the number of conspecific neighbors in various distance and size classes. Density-dependent effects on survival and growth were strong in Faramea. Performance of 1-8 cm dbh plants declined with increasing numbers of adult neighbors within 1 m, 1-2 m, and 2-4 m, but neighbors at 4-6 m had no effect. Performance also declined with increasing numbers of juvenile neighbors lt 4 cm dbh, but the effect was less pronounced. Saplings of Faramea grew poorly in areas of high juvenile density within 30 m, independent of the effects caused by neighbors within 4 m. In contrast to Faramea, Desmopsis showed no density dependence in survival nor in growth. For recruitment, however, the two species showed similar patterns: recruit density was lower in regions with an adult conspecific within 1 or 2 m distance, but higher in regions with high densities of adult or juvenile conspecifics between 2 and 30-60 m. Desmopsis must have suffered density-dependent effects at stages lt 1 cm dbh, but the effect vanished by the 1 cm dbh stage. In Faramea, strong neighborhood effects were evident in all size classes lt 8 cm dbh.