Luquillo LTER Program 4: Understanding Change in the Ecosystems of Northeastern Puerto Rico

The Luquillo Long-Term Ecological Research Program (LUQ) focuses on understanding factors driving long-term change in tropical forest ecosystems in the Luquillo Mountains of Puerto Rico. Building on an earlier emphasis on natural disturbances (hurricanes, landslides, droughts, floods) and ecosystem responses, LUQ will continue studies of ecosystem structure and processes in mid-elevation tabonuco forest, extend research into other forest types along an elevation gradient, and begin investigations of regional-scale processes affecting the Luquillo Mountains. Four approaches will be used: long-term experiments and measurements, comparative analyses among different forest communities, gradient analysis from forest to urban, and synthesis using conceptual and simulation models. Mounting evidence suggests that increasing hurricane intensity, declining rainfall in the mountains, and rising temperature in lowland urbanized areas can significantly affect the ecosystems of the Luquillo Mountains. In this context, the overarching question is: How do changes in disturbance regime and climate alter biogeochemical cycles, biotic structure, and ecosystem services? This leads to three specific questions addressing key elements of the LUQ conceptual framework: 1) What controls variation in carbon and nutrient fluxes, and how are these variations modified by disturbance? Many processes in the Luquillo Mountains exhibit well defined seasonality and links to climate. Understanding these relationships is essential for determining the sensitivity of biota and biogeochemical cycling to environmental change. 2) Are changes in temperature, rainfall, light and wind (climate) along the Luquillo elevation gradient sufficient to explain variation in biogeochemical processes and biotic structure? LUQ proposes to study linear and non-linear trends in climate with elevation in the Luquillo Mountains as drivers of ecosystem processes and the distribution of organisms. By improving understanding of the importance of biotic and abiotic factors in determining the distribution of organisms over spatial gradients in tropical mountains, scientists will increase their ability to understand the effects of change. 3) How important are changes in land-use in determining long-term ecosystem biogeochemistry, biotic structure, and services? Land-use and land-cover are changing dramatically in northeastern Puerto Rico in response to socioeconomic changes. LUQ proposes to examine the long-term effects of land-use and land-cover change on a range of features, including regional and local climate, tree species composition, stream ecology, and a key ecosystem service: the delivery of clean water for humans. The proposed research will provide an improved scientific framework for the management of tropical ecosystems and ecosystem services. It will do so both through conceptual advances and documentation of human disturbance and ecosystem response. The project will continue to produce a cadre of young and minority scientists who are versed in linking population and ecosystem approaches to evaluating environmental change, and will provide them with skills that can be applied in tropical regions or elsewhere. LUQ has developed a comprehensive education program involving teachers at a network of six high schools and a web-based middle school curriculum for teaching ecology. Additional outreach activities are directed at improving the general public's appreciation of the water resources provided to surrounding towns by streams draining the Luquillo Mountains.