Themechanism of general flowering in Dipterocarpaceae in the MalayPeninsula is revealed through field survey and meteorological dataanalyses. The regions of general flowering coincide with those whichexperienced a low night-time temperature (LNT) c. 2 mo beforeflowering. This supports the hypothesis that low air temperature inducesthe development of floral buds of dipterocarps. LNT was found to becaused by radiative cooling during dry spells in winter when thenorthern subtropical ridge (STR) occasionally migrates southwards with adry air mass into the equatorial region. LNT events usually occur in LaNiña episodes, not in El Niño episodes as believedpreviously. This is because the southward migration of the STR isassociated with the intensification of local meridional HadleyCirculation in the western Pacific, which is strengthened in a LaNiña episode. Results suggest that El Niño-like climatechange in increased atmospheric carbon dioxide concentrations may becritical for the tropical rain forest biome in south-east Asia.
