Abstract
We made litter fall observations in a West Sumatran tropical rain forest every 2 weeks through 3 years (including the drought year, 1997). Seasonal changes in long-term average rainfall were bimodal, but even in the two dry seasons average monthly precipitation was > 200 mm. Leaf-fall rates in a year with normal rainfall peaked in the first dry season; leaves made up one-third of mean annual litter fall. Larger trees had highly synchronized leaf fall during the peak shedding period. Smaller trees shed simultaneously during severe drought. Twigs < 0.5 cm diameter tended to fall in proportion to the 3/2 power of leaf-fall rates; therefore, we considered autonomous twig fall in relation to the pipe model theory. Variances in reproductive organ shedding rates (seasonal and annual) were larger than those of leaves and branches, possibly because of the higher susceptibility of reproductive parts to drought. Reproductive fall rates in the year with normal weather peaked in May (flowers) and August (fruits). Seasonal patterns of flowering and fruiting were classified into three groups. Understory species had an “extended flowering” pattern. We discuss phenological patterns found in this very high humidity climate and the impacts of increasingly frequent droughts.
