Impacts of dry and hazy weather in 1997 on a tropical rainforest ecosystem in West Sumatra, Indonesia

An equatorial rainforest in the coastal region of West Sumatra suffered a long period of dry and hazy weather in 1997. Canopy trees with higher growth rates before the event had reduced growth rates during the 8 months from June 1997 to an average of 23% of their 1996 growth rate. The size-dependency of growth depression in forest trees greater than 5 cm in stem diameter could be observed during this period. The weather induced defoliation, and high litterfall rates of leaves continued throughout the period. The impacts of the weather on growth rates were analyzed by using Saekis mathematical model for community production. This model suggested that the great reduction in growth-rates of active canopy trees would be caused mainly by the interacting effects of potential photosynthetic rate and leaf biomass because of their sensitive responses to drought. In the severe weather conditions, these variables were estimated to have decreased to more than 50% of their 1996 values.