Seed and seedling ecology of a monocarpic tropical tree, Tachigalia versicolor

Tachigalia versicolor (Leguminosae: Caesalpinoideae) is a monocarpic canopy tree species on Barro Colorado Island, Panama. For the weighted average of 2 trees, percentage of offspring surviving from dispersed seed to germination, 1 yr, and 2 yr was 30, 7.2, and 4.3% respectively. The large seeds (500-600 mg) suffered greater mortality in absolute numbers than did seedlings. Major mortality agents of seeds were bruchid beetles (Amblycerus tachygaliae) and terrestrial vertebrates, while vertebrate herbivores and damping-off fungi killed seedlings. Seeding survival and growth were enhanced under canopies of dying T. versicolor adults, relative to under canopies of living conspecific and nonconspecific adults. Most 2-yr-old seedlings occurred within 0-40 m from the parent trees, reflecting the original peak of the distribution of wind-dispersed seeds. Few seedlings persisted beyond 40 m. Seedling survival in the first 2 mo was higher in shaded understory due to higher vertebrate herbivory in sun. Seedling growth and survival beyond 2 mo was higher in light-gaps. T. versicolor seedlings exhibited a wide range in maximum net photosynthetic rate when grown in contrasting light conditions, and could acclimate to sudden increase in light level by means of morphological and physiological adjustments of newly developed leaves. Relative to nonmonocarpic wind-dispersed tree species in the same community, T. versicolor ranks near the top in its seed mass, dispersal capability, photosynthetic flexibility to contrasting light conditions, and probability of seedling survival in the shaded understory through 1 yr. These characterstics enable T. versicolor to establish large numbers of seedlings. -from Authors