Comparative Phenological Studies of Treelet and Shrub Species in Tropical Wet and Dry Forests in the Lowlands of Costa Rica

Abstract

SUMMARY (1) During 1970-73, marked individuals of 154 treelet and shrub species at a Wet forest site and 95 species at a Dry forest site in Costa Rica were observed regularly at 4- to 6-week intervals for changes in leafing, flowering and fruiting. (2) All the shrubs in the Wet forest were evergreen. New leaves were produced continually throughout the year by half the species, although this behaviour was more pronounced in species of secondary forest (87%0). For the community as a whole, leaf production was equable throughout the year. (3) About half of the treelets and shrubs in the Dry forest were deciduous. Hill forest treelets and shrubs produced most leaves at the beginning of the wet season, Riparian forest treelets and shrubs had a peak in leaf production near the end of the wet season, and leafing of species of secondary forest was continuous throughout the wet season. Most treelets and shrubs were bare or dormant during the dry season. Leaf loss was greatest during February. (4) There were no consistent peaks of flowering for treelet and shrub species in the Wet forest, but flowering levels tended to be greatest in the first half of each year. (4) Continuous flowering was rare among Wet forest treelets and shrubs, being characteristic of only a few species of secondary forest. Most Wet forest treelets and shrubs (64%) had several flowering episodes each year, with the episodes separated by 3-5-month intervals. Species with only a single brief synchronous flowering period were rare. (6) By contrast, flowering amongst Dry forest treelets and shrubs showed a pronounced seasonal pattern. The Hill forest treelet and shrub community had a sharp peak of flowering at the beginning of the wet season, while, in contrast, the Riparian forest treelet and shrub community had its major flowering at the end of the wet season. Most Dry forest species flowered synchronously once or twice each year. (7) There was a weak tendency for maximum fruiting of Wet forest shrubs in the second half of each year. A short period of fruit maturation (4 months) was shown by most Wet forest treelets and shrubs, although one species had a fruit maturation time of 27 months. Ten species of Wet forest treelets and shrubs flowered at least once during the study, but failed to produce fruit.