Forests affected by frequent and intense typhoons challenge the intermediate disturbance hypothesis

Abstract

Tropical cyclones (hurricanes and typhoons) are extreme disturbances that have a significant impact on ecosystem structure and processes. The intermediate disturbance hypothesis (IDH) generalizes disturbance–diversity relationships but its validity is hotly debated. The IDH has been challenged both theoretically and with results from experimental studies; however, few studies have empirically tested the proposed mechanisms of IDH using results from the actual ecosystems. In this commentary, based on empirical observations from studies on the interactions between tropical cyclones and forest dynamics, we outlined seven possible outcomes of gap dynamics and tree diversity as a result of different frequency and intensity combinations. We argue that the lack of distinction and differentiation between disturbance intensity and severity, and the overlooked role of tree mortality, seedling recruitment, and tree adaptations limit the applicability of IDH in predicting the disturbance–diversity relationship. In the era of climate change characterized with more frequent climate extremes and natural disturbances, we should move beyond the generalizations and directly address the processes leading to the observed disturbance–diversity relationships to make reliable predictions.