Testing the environmental prediction hypothesis for community-wide mass flowering in South-East Asia

General flowering, in which hundreds of species synchronize their flowering at multi-year intervals, is a puzzle to ecologists. It is hypothesized that species taking part in general flowering time their reproduction to meet favorable environmental conditions for seedling establishment. We tested this environmental prediction hypothesis using 14-year weekly flower records of five Shorea species (Dipterocarpaceae) and daily meteorological data in a lowland rain forest in Malaysia. We first investigated causal inference between three potential flowering triggers (cooling, drought, and the synergistic signal of cooling and drought) and flowering. We then explored the causality between flowering triggers and moisture condition during seedling establishment. Our results demonstrated that the synergistic signal of cooling and drought causally influences flowering phenology with the highest predictability for the timing of flowering. Both drought and the synergistic signal of cooling and drought are causally linked to favorable wet conditions during seedling establishment, but the predictability of future rainfall by the synergistic signal was higher than the drought alone. These results support the environmental prediction hypothesis and raise the question as to whether climate change allows the prediction to hold for plant regeneration in the future.