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 the novel approaches advanced our understanding of GF, it is usually difficult to know whether the mathematical formulation reasonably well represents the complex and dynamic processes involved in GF. In the present study, we collected a 17-year set of community-wide phenology data during 1993 to 2011 from Lambir Hills National Park in Borneo, Malaysia, and analyzed it using a model-free approach, empirical dynamic modeling (EDM), that does not rely on specific assumptions about the underlying mechanisms, to overcome and complement the previous limitations. By using EDM, we found that GF in the forest in Lambir Hills National Park is synergistically driven by cool air temperature and drought, which is consistent with the previous studies. Also, we found that cumulative meteorological variables, rather than instantaneous values, drive GF with delayed effects, which is also consistent with the previous studies. Interestingly, the present study showed that effects of cumulative meteorological variables on GF changed through time, which implies that the relationship between GF and meteorological variables may be influenced by other factors such as plant/soil nutrient resource dynamics. Future studies integrating novel mathematical/statistical frameworks, long-term and large spatial scale ecosystem monitoring and molecular phenology data are promising for better understanding and fore-casting of GF events in tropical forests in Southeast Asia.