TREE MORTALITY IN MATURE LOWLAND TROPICAL MOIST AND TROPICAL LOWER MONTANE MOIST FORESTS OF VENEZUELA

We examined patterns of mortality from long-term (up to 25 yr) forest inventory data collected from 17 0.25-ha plots representing mature tro pical lowland moist forest and tropical lower montane moist forest lif e zones in Venezuela. Annual mortality rates varied greatly among plot s and differed when mortality was calculated on a frequency basis (% s tems dying annually) versus a biomass (% total aboveground biomass dyi ng annually) basis. Mortality rates ranged from 0. 5 to 3.3 percent (s tems) and 0. 1 to 3.9 percent (biomass). Annual mortality rate of stem s versus mortality rate of biomass differed by as much as 20 percent w ithin a plot; greater mortality rate of biomass on a yearly basis was attributable to the death of large trees. Annual percent mortality was independent of life zone, diameter class within life zone, and crown class. The majority of trees died standing (64%) followed by fallen (1 7%), snapped (I 1%), and other unknown causes (I 1%). Estimates of the mean half-life of all plots were 36.9 and 42.5 yr based on stems and biomass, respectively, in the tropical moist forest, and 39.3 and 36.3 yr, respectively, in the tropical lower montane moist forest. Large d iameter classes had the longest half-lives. Similarity in stem and bio mass based half-lives within a life zone suggests that although there is great variability at the individual plot scale, stems and biomass y ield similar estimates of mortality at the larger life zone scale.