Resilience of a subtropical rainforest to annual typhoon disturbance: Lessons from 25-year data of leaf area index

Quantifying ecosystem resilience is critical for predicting how shifts in disturbance regime affect ecosystem structure and function as a result of recent climate change. Studies of disturbance-ecosystem interactions often focus on one or a few disturbance events but the interactions may vary considerably among disturbance events. We used a 25-year LAI (leaf area index) record of the Fushan Experimental Forest (FEF) of northeastern Taiwan to explore forest LAI resilience to annual typhoon disturbance. The four typhoons of 1994 caused the most dramatic change of LAI in both the magnitude and the rate, as well as the longest time for a full recovery. However, typhoons varied in their effects, and not all intense typhoons caused major impact suggesting that result derived from one or a few disturbance events is unlikely to capture the full spectrum of disturbance effect. Using LAI of 4.26 measured following a non-typical year of no typhoon occurrence as a reference, it took 11─16 years before the predicted LAI to return to the reference level, which represents the resilience (time to return) of the forest LAI under minimal typhoon effects. Using the event-based analyses, the average degree of return was 0.86, with values as low as 0.45, suggesting that the LAI of the FEF is not always able to fully recover within the inter-typhoon time period (<1 year). Once returned to the reference state, the LAI of the FEF stayed at the reference state for several months to several years. With annual typhoon disturbance and a return time longer than one year and may be up to more than one decade, the LAI of the FEF is constantly undergoing the disturbance-recovery process and rarely reaches an equilibrium state. Therefore, a system experiencing frequent disturbance such as FEF might be better characterized by non-equilibrium temporal dynamics of its key functions.