Phenology of tropical lower montane forests in southern highlands of Vietnam: leafing is associated with precipitation but flowering is not

The premise of the study Though phenological studies in montane forests are important, particularly in tropical Asia where primitive angiosperms are found, the phenology in these forests is still poorly understood. To characterize the phenological patterns and reveal the relationships between meteorological factors and phenology, we observed the leafing, flowering, and fruiting phenology in the tropical montane forests of Vietnam. Methods We observed the leafing, flowering, and fruiting phenology of 91 species every three months in five plots (elev. 1460–1920 m) in Bidoup-Nui Ba National Park, Vietnam, and analyzed how the number of species that were leafing, flowering, or fruiting varied in relation to precipitation, temperature, or daylength. Key results The leafing phenology showed a peak at the beginning of the wet season (April) and was significantly influenced by all of day length, precipitation, and temperature. The flowering phenology did not show any distinct peaks and was influenced by day length and precipitation. The fruiting phenology showed a low peak from the wet season (July) to the beginning of the dry season (December) and was not significantly influenced by any of the meteorological factors. Main conclusion The community-wide phenological patterns of leafing, flowering, and fruiting in the tropical montane forest of Bidoup-Nui Ba are unique among the tropical forests of East and Southeast Asia. In particular, our observation suggests that masting in tropical montane forests may be an ancestral state of both general flowering in tropical rainforests and masting found in temperate forests in East and Southeast Asia.