COS 85-4 - Tree rings as a global proxy record of long-term changes in tropical cyclone activity and their impact on forest ecosystems under changing climate

Background/Question/Methods

Tropical cyclones (TCs) are important drivers of forest dynamics, and it is predicted that their importance will increase. Opinions on the past variability of the TC land interaction in the western North Pacific are conflicting, with some studies detecting a decrease, others detecting an increase, and still others showing no trend in the destructive potential of TCs. Instrumental records are too short to satisfactorily determine whether detected trends in TC activity are within the range of long-term natural variability or are associated with climate change. Thus, unified and high-resolution proxy records from multiple locations are essential for understanding the long-term trends in TC activity over a wider area. In addition, little is known about the long-term (over several decades or centuries) impact of TCs on forest growth, diversity, and regeneration although these are key aspects of predicting the consequences of globally accelerating forest diebacks on carbon stocks and forest biodiversity, as well as humankind. Here we aimed to determine (i) history and potential shifts in TC activity over several sites in East Asia and USA and (ii) impact of TCs on forest ecosystems, including impact of recent changes in TC activity.

Results/Conclusions

Our results indicate significantly increasing TC frequency in the areas formerly situated at the edge of TC activity and thus provide evidence supporting the broad relevance of poleward migration of TCs. In addition, we identified recent increase in TC intensity as well as high frequency of landfalling TCs. Our findings significantly enhance current understanding of the effects of climate change on TCs and emphasize the need for determination of long-term variation of past TC activity to improve future TC projections. In addition, we identified the gradient of TC activity as the main driver influencing forest canopy dynamics and thus changes in life-history traits for several dominant tree species in East Asia. Flexibility in growth strategies enabled the studied species to cover extensive areas and indicates that they will be able to cope with shifts in disturbance regimes induced by the poleward migration of TCs and increasing TC intensity. We suggest that utilization of TC proxy data, as tree rings, is necessary to place variability in TC activity in a historical, preindustrial context and provides a benchmark for understanding TC drivers on multi-centennial scale.