<S1-1> Long-term monitoring of plant reproductive phenology and observation of general flowering in Lambir Hills, Sarawak

Abstract

General flowering (GF) is a community-wide masting phenomenon, which has thus far been documented only in aseasonal tropical forests in SE Asia. It is also one of the most spectacular and mysterious phenomena in tropical biology. GF occurs at irregular intervals of less than a year to several years. During such an event most dipterocarp trees and many other plants from shrubs to emergent trees to epiphytic orchids flower over roughly a three-month period. Conversely, flowers are scant between general flowering events. This type of community-wide masting has only been documented from this region. Since 1993, we have observed plant phenology from tree towers, walkways and a canopy crane in Lambir Hills National Park. We chose 486 individual plants of 300 species in 56 families to monitor phenology at the community level in 1993. The long-term monitoring of the forests have provided important clues for understanding the phenomenon. Proximate factors of general flowering have been the subject of controversy over the last decades. From the present observations, we concluded that drought was the most plausible trigger for general flowering. We have recorded a few large and many smaller general flowerings during the 20 years of observation. All flowering peaks were preceded by dry periods. The effects of such large fluctuations in flowering and fruiting intensities on population dynamics and host ranges of flower visitors and seed predators have been intensively investigated in Lambir Hills. Examinations in the field and laboratory have often revealed rather loose interactions, and great variations of population dynamics among taxonomic groups. Although many questions still remain to be answered, there is no doubt that general flowering has played a dominant role in structuring the hyper-diverse ecosystem of the dipterocarp forests.