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 had no effect. Performance also declined with increasing numbers of juvenile neighbors <4f 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 <1 cm dbh, but the effect vanished by the 1 cm dbh stage. In Faramea, strong neighborhood effects were evident in all size classes <8 cm dbh.