Dynamic and synergistic influences of air temperature and rainfall on general flowering in a Bornean lowland tropical forest

Supra-annually synchronized flowering events occurring in tropical forests in Southeast Asia, known as general flowering (GF), are "spectacular and mysterious" forest events. Recently, studies that combined novel molecular techniques and model-based theoretical approaches suggested that cool temperature and drought synergistically drove GF. Although these advanced our understanding of GF, it is still difficult to know whether the individual-based molecular measurements and model-based mathematical representations reasonably well capture the complex and dynamic GF processes at the community level. In the present study, we collected a 17-year set of community-wide phenology data from Lambir Hills National Park in Borneo, Malaysia, and analyzed it using a model-free approach, empirical dynamic modeling (EDM), which does not rely on specific assumptions about the underlying mechanisms, to overcome and complement the previous limitations. We found that GF in the region is driven synergistically, not independently, by cool air temperature and drought, which is consistent with the previous studies. More importantly, our model-free approach showed for the first time that effects of cumulative meteorological variables on GF changed over time. The time-varying influences of meteorological variables on GF imply that the relationship between GF and meteorological variables might be influenced by other factors such as plant/soil nutrient resource dynamics. Our study provides a novel insight about the mechanism underlying the spectacular tropical forest event GF, and future studies integrating advanced mathematical/statistical frameworks, long-term and large spatial scale ecosystem monitoring and molecular phenology data are promising for achieving better understanding and forecasting of GF events in Southeast Asia.