LUQUILLO EXPERIMENTAL FOREST
LONG-TERM ECOLOGICAL RESEARCH PROJECT

Overview of the research project (continues)
Many Luquillo LTER projects occur in El Yunque National Forest, which covers 11,231 hectares and reaches 1079 m above sea level (see Environmental Setting).  El Yunque  has a warm and wet climate and includes a variety of tropical habitats and forest types and streams, and a high diversity of plants and animals (see Geology, Climate and Hydrology, Food Webs, Streams).  A key feature of these ecosystems is disturbance. Hurricanes, landslides, and human disturbance have shaped the forest, and research by LUQ has stimulated a new appreciation of the significance of large-scale disturbances in tropical forested ecosystems and the key role of plants and animals in shaping the response to these events (see Disturbance and Recovery, Landslides, Forest Dynamics). Hurricanes occurring one and 10 years after Luquillo LTER began provided landscape-scale natural experiments which are still followed closely.
Among the most important findings from these natural experiments is that detrital dynamics plays a central role in forest recovery by influencing carbon and nutrient storage and flow. Therefore, in the context of the overall research goal, the most recent research questions are: (1) How do climatic factors, litter quality, and detritivore diversity regulate decomposition of detrital pulses? (2) How do terrestrial and aquatic food webs differ in their response to detrital pulses? (3) What is the effect of disturbance frequency on nutrient cycling, plant community composition, and the accumulation of soil organic matter? (4) To what degree is the export of carbon and nutrients from watersheds a result of soil characteristics that are affected by detrital dynamics? (5) How do elevation-related changes in climate impact plant and detritivore communities, and how do these feed back on the quantity and quality of litter inputs and decomposition? The LUQ research plan for answering these questions is based on 1) long-term measurements of forest and stream response to natural and anthropogenic disturbance, 2) associated short- and long-term manipulative experiments to develop a process-level understanding of results from our long-term measurements, 3) validation of this understanding through parallel experiments and measurements along gradients of climate and species richness, and 4) comparison of results from Luquillo LTER with other LTER and non-LTER sites (see Proposals, and Methods for detailed protocols).
This work addresses critical issues about global climate change, tropical forest carbon dynamics, and changes in biodiversity by: 1) chronicling the effects of repeated hurricane disturbance and climatic gradients on the long-term dynamics of a tropical forest ecosystem, 2) providing long-term assessments of carbon storage in tropical biomass and soils, and 3) examining the degree to which species and functional groups contribute to detrital dynamics and the ability of an ecosystem to recover following disturbance. By extending an understanding of El Yunque to other disturbance-driven systems, Luquillo LTER is making significant contribution to our knowledge of the mechanisms by which disturbance structures ecosystems.

Luquillo LTER Scientists and Facilities
Principal Investigators of Luquillo LTER are Nicholas Brokaw – ITES and Ariel E. Lugo – IITF.  There are 23 additional senior researchers from Puerto Rico, the United States, and the United Kingdom in Luquillo LTER, as well as many Associate Researchers, students, and technicians (People link).

The El Verde Field Station (station link) with living and laboratory facilities for up to 25 scientists is maintained by Institute for Tropical Ecosystem Studies (ITES) in El Yunque.  The field station provides collections of local plants and animals; a laboratory with light meters, balances, microscopes, pH meters, hoods, etc.; line power backed up by a generator; and gas, air, and vacuum lines. Luquillo LTER is headed by researchers from ITES and the Forest Service, including the International Institute of Tropical Forestry (IITF). Among the resources available through IITF (IITF link) are: the Bisley Experimental Watersheds, the Sabana Field Research Station, an analytical laboratory for soils and vegetation, research nursery, an extensive tropical forestry library, and a research herbarium.

Numerous databases are compiled by Luquillo LTER, including: maps of geology, soils, vegetation, disturbance history; seven sets of aerial photography since 1936; air temperature, precipitation since 1909; solar radiation, wind speed and direction, relative humidity; NADP precipitation since 1984; chemical composition of precipitation, dryfall, cloudwater, bulk soil, soil solution, throughfall, stemflow, streamwater, plant tissue, animal tissue, fungal tissue; vegetation composition, above- and below-ground biomass, tree growth/mortality, litterfall, litter decomposition, wood decomposition, mycorrhizal associations, phenology; population records and biomass of terrestrial and aquatic fauna; streamflow. Many of these databases are available on the web.