DENSITY-DEPENDENCE IN 2 UNDERSTORY TREE SPECIES IN A NEOTROPICAL FOREST

Density dependence was examined in two species of neotropical treelets , Faramea occidentalis and Desmopsis panamensis, in a 50-ha plot on Ba rro Colorado Island in Panama. Survival and growth probability of plan ts larger than 1 cm dbh (diameter at breast height), and recruitment i nto the 1-cm class, were assessed as a function of the number of consp ecific neighbors in various distance and size classes. Density-depende nt effects on survival and growth were strong in Faramea. Performance of 1-8 cm dbh plants declined with increasing numbers of adult neighbo rs 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 neighbo rs <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. Fo r recruitment, however, the two species showed similar patterns: recru it 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 ju venile conspecifics between 2 and 30-60 m. Desmopsis must have suffere d density-dependent effects at stages < 1 cm dbh, but the effect vanis hed by the 1 cm dbh stage. In Faramea, strong neighborhood effects wer e evident in all size classes < 8 cm dbh.