Response and recovery of tropical forests after cyclone disturbance

Abstract:

Tropical cyclones dominate the disturbance regime experienced by forest ecosystems in many parts of the world. Interactions between cyclone disturbance regimes and nutrient availability strongly influence forest ecosystem dynamics. However, uncertainty exists over the importance of soil fertility properties (i.e., total soil phosphorus-P concentration) in mediating forest resistance and recovery from cyclone disturbance. We hypothesized that forests on soils with low total P (e.g., developed on limited-P parent material) have a higher resistance to but a slower recovery from cyclone disturbance than forests on high P soils. We investigated cyclone impacts on litterfall, an essential conduit for nutrient recycling in forest ecosystems. We compiled site-level forest litterfall data from 56 studies and datasets associated with 18 naturally-occurring and one simulated tropical cyclone in 25 sites within five regions (Taiwan, Australia, Mexico, Hawaii, and the Caribbean) and four cyclone basins. We calculated the effect sizes of cyclone disturbance on the litterfall mass and litterfall fractions, and their nutrient (P and nitrogen-N) concentrations and fluxes during the first (< five) years post-disturbance across a total soil P gradient. We also assessed the effect of 22 covariates on the degree of cyclone impact on litterfall. Total litterfall mass flux increased by 4820% following cyclone disturbance, with an increase in the wood fraction by over 14000% and in the leaf fraction by 3000% relative to their respective long-term pre-disturbance means. Such an initial increase in litterfall mass reflects the magnitude of cyclone-derived plant material input to the forest floor. Among 22 covariates, soil P and region were the best predictors of wind effect on total litterfall mass, explaining 80% of the variance. The effect sizes increased linearly with soil P and region, from significantly lower in Taiwan (low-P) to largest in the Caribbean (high-P). Total litterfall P and N fluxes increased significantly post-cyclone, whereas the increase in leaf P flux was twice as that in N flux. Results highlight the importance of understanding the interactions between disturbance and nutrient gradients in forest ecosystems to understand forest responses to altered disturbance regimes expected under climate change.