Spatial and temporal variability in the structure of a tropical forest

This study examines spatial and temporal variation in the forest structure of the Kibale National Park, Uganda by contrasting tree density, tree size, and forest composition among four areas each separated by less than 15 km, and by quantifying changes in the composition of one of these forests over a 20-year period. Densities of some tree species differed markedly between sites, and some species common at one location were absent at others. Monthly phenological monitoring demonstrated that it was not uncommon for phenological patterns to differ between the forests. To examine temporal variation in the tree composition over a 20-year period, a sampling regime that was carried out in the early 1970s was replicated on the floristic composition of one of these sites, using identical methods in the same sampling areas. While no form of human intervention occurred in this area between the early 1970s and 1992, there were marked changes in the densities of some tree species. Twenty-seven percent of the identified species increased in abundance, 33% decreased, and 40% remained relatively unchanged. The observed spatial and temporal variation in forest composition could be the result of abiotic factors, such as altitude or rainfall, or biotic factors such as elephant and/or human influences on ecosystem dynamics; the implications of this variation for frugivores are discussed.