Species-specific responses to extreme hydrological disturbances depend on event sequences

Climate change is projected to dramatically increase the probability and frequency of extreme weather events such as floods and droughts, and detrimentally affect the structure, function and services of terrestrial and coastal ecosystems. However, ecological studies to date have focused mainly on the consequences of individual extreme events, largely ignoring the confounding impacts of multiple extreme events and their sequences.  Here, we show that co-occurring, dominant tree species in wetland ecosystems differ in their responses to extreme hydrological disturbances of flood and drought. In addition, the sequential order of flood or drought imposed resulted in significantly different species responses. The sequential effects can be mitigated for certain species by imposing a period of optimal conditions between two extreme events which, under certain circumstances, was observed to positively stimulate plant growth for some species.  These findings lead us to believe that the assessment of the impacts of multiple extreme climatic events cannot be modeled by simply summing the projected effects of individual extreme events. Instead, multiple extreme events like those associated with climate change should be evaluated within relevant spatial, temporal and sequential contexts. Our findings are likely to provide critical information for the successful management and restoration of ecosystems that are projected to experience increases in extreme weather events and hydrological fluctuations.  The results will improve our modeling effort by allowing more precise assessments and strengthen our ability to predict terrestrial ecosystem responses to various projected climate scenarios.