TROPICAL TREE SEEDLING DYNAMICS - RECRUITMENT PATTERNS AND THEIR POPULATION CONSEQUENCES FOR 3 CANOPY SPECIES IN PANAMA

A study of seedling demography of three shade-tolerant canopy tree spe cies (Quararibea asterolepis, Trichilia tuberculata, and Tetragastris panamensis) was initiated to integrate with long-term studies of tree fruit production and of tree population dynamics on Barro Colorado Isl and, Panama. Over a five-year period, all seedlings (height <50 cm) an d small saplings (height greater-than-or-equal-to 50 cm to dbh 1 cm) w ere measured and monitored in permanent tree-centred transects (N = 10 -11 trees per species). Survival rates increased with plant size class and were similar among species. Maximum height growth rates increased with increasing plant size, but average growth rates did not; this di sparity suggests the importance of release from understorey suppressio n for long-term recruitment success. Among the three species, Quararib ea had the lowest standing seedling densities and almost no sapling re cruitment, whereas Tetragastris had the highest densities of both seed lings and saplings; Trichilia seedling and sapling densities were inte rmediate. In all three species, a few trees produced very high seedlin g and sapling densities in comparison with the sample average. All thr ee species exhibited a year of exceptionally high new seedling recruit ment during the study period; these good years were not coincident amo ng the species but instead reflected the species' phenological differe nces. Since seedling survival becomes relatively constant and high aft er the first few years of life (c. 80% y-1), such large new cohorts pe rsist as a year-class effect in the seedling population and thus maint ain seedling numbers over time. The interspecific differences in seedl ing and sapling dynamics were consistent with overall 10-year trends o f a declining Quararibea population, a stable Trichilia population, an d an increasing Tetragastris population.