UC Berkeley

The effects of climate change are causing widespread changes in forest disturbanceregimes, with significant implications for ecosystem carbon (C) and nutrient cycles in wet tropical forests. These humid ecosystems are faced with multiple types of natural disturbances, including hurricanes and drought, both of which are projected to increase in frequency due to climate change. Understanding future trajectories of wet tropical forests exposed to novel disturbance regimes requires the study of belowground biogeochemical responses to disturbance at multiple temporal and spatial scales. In this dissertation, I focused on studying the responses of soil biogeochemistry to hurricanes and drought in a wet tropical forest in Puerto Rico. In the first chapter, I present the soil biogeochemical responses to a long-term (10 yr) ecosystem manipulation experiment called the Canopy Trimming Experiment, which revealed the significant impact of hurricane-induced debris deposition on soil biogeochemistry throughout the soil profile. In the second chapter, I make use of an ecosystem biogeochemical model (DayCent) to study the long-term (decades to centuries) effects of changes in the hurricane disturbance regime on soil biogeochemistry, demonstrating the significance of changes in live biomass and soil C pools due to increases in hurricane frequency for ecosystem-scale C fluxes. In the third chapter, I present the results of a throughfall exclusion experiment that demonstrated the rapid and significant effects of drought on soil microclimate and biogeochemical cycling, even within the context of a Category 4 hurricane that had a major impact on the site. This unexpected event gave me the opportunity to study the interaction between these two major disturbances in the field, revealing important insights for better understanding the consequences of changing disturbance regimes for soil biogeochemical cycling and the implications for wet tropical forests.