Reproductive phenology over a 10-year period in a lowland evergreen rain forest of central Borneo

1. The aim of this study was to document patterns in tree reproductive phenology in a rain forest of central Borneo and examine relationships between phenology and climatic patterns. 2. A 10-year data set (1990-2000) of monthly observations of flowering and fruit production of 171 trees (including 39 members of the Dipterocarpaceae) at Barito Ulu, Central Kalimantan, Indonesia, showed that most trees (73%) underwent reproductive activity on a supra-annual timescale. 3. There were three general flowering (GF) events, in 1991, 1994 and 1997, which were preceded by major drought periods (30-day sliding total rainfall of less than 100 mm for more than 10 days) in which at least 40% of dipterocarps and at least 18% of all other trees underwent synchronized reproductive activity; there was also a minor event in 1990. Around 1.3% of trees flowered and 3.8% produced fruit in months outside of these four events. 4. At the community level, the strongest negative correlation was found between the percentage of flowering individuals and total rainfall in the preceding 150 days. 5. Within three genera of dipterocarps examined in more detail (Dipterocarpus, Shorea and Vatica) there were clear and consistent patterns of sequential flowering with certain species flowering early in the GF events and others towards the end of these events. 6. Our results confirm the importance of large-scale climatic fluctuations (El Nino-Southern Oscillation) on plant reproductive phenology in South-east Asian tropical forests and indicate that drought may be a more important cue than low night-time temperatures.