|LUQ Research Categories||Project Title||Project Description or Abstract||Investigators|
|Research in the secondary forest La Torrecilla, Barranquitas 2||
During the years of 1986 and 1987, we selected a private area in the Forest “La Torrecilla”, located at the Barrio Barranquitas, for the development of a long-term study with the help of the International Institute for Tropical Forestry. Our study area is located at the Barrio Barrancas of Barranquitas at 3,093 feet above sea level. The area has been classified as a secondary forest in the past because it was used for agriculture since the XIX Century until 1940, to cultivate coffee. In our forest, one of our main water source originates: The Manatí River. The Forest is the lung which efficiently purifies our air.
|Ecosystem dynamics||Riparian Carbon and Nitrogen Dynamics||
Hydrologic and chemical characteristics were determined for both riparian and hyporheic subsurface flow along a 100-m reach of a sandy-bottom tributary of the Rio Icacos in the Luquillo Experimental Forest, Puerto Rico. Hydrologic data (vertical hydraulic gradient and hydraulic conductivity of streambed sediments) and the topographic and morphological features of the watershed indicated diffuse inputs of groundwater from the near-stream riparian zone along this site. Cumulative groundwater discharge, determined by tracer dilution techniques, was ~1.5 L/s or 10% of the total stream discharge. Spatial heterogeneity in hydrologic and chemical properties of riparian and hyporheic sediments was large. Hydraulic conductivity explained much of the variation in NH4-N and dissolved organic carbon (DOC) concentrations, with highest concentrations in sites having low conductivity. A mass-balance approach was used to examine the influence of the near-stream zone on nutrient transport and retention. Outwelling riparian groundwater had the potential to increase stream N concentrations by up to 84% and DOC concentrations by up to 38% along our 100-m reach. Because stream concentrations were constant downstream despite this input, we conclude that significant N and C retention or loss were occurring in the near-stream zone. Lotic ecosystems and their associated riparian groundwater can have a quantitatively significant impact on the nutrient budgets of tropical headwater catchments.
|William H. McDowell|
|Environmental monitoring||River Education Program||
The River Education Program (Luquillo-LTER)is a portal to information about the natural resources of El Verde, Luquillo Experimental Forest, and El Yunque National Park. By reporting on what has been learned from research and monitoring in these areas, we hope to increase public awareness of new findings and encourage studies that will help guide management decisions.
NOTE: A web site was developed by O. Perez-Reyes at: https://sites.google.com/a/ites.upr.edu/luquillo-lter/home
|Vegetation dynamics||Seed Germination and Light Quality||
Light level is an environmental property monitored at LUQ. Light level, soil moisture, and temperature simultaneously increase after disturbance and may interact with the pulse of detritus to affect subsequent community and ecosystem changes. For example, increased light promotes the establishment of pioneer and shrub species, but the litter deposited by the hurricane inhibits the germination of these same species (Guzmán-Grajales & Walker 1991). (See LUQ lTER Proposal 2002 for mor details. )
The L-CENTURY predicts that light is the dominant regulator of NPP along the gradient (Wang 2001) and in LUQ LTER 3 we hypothesize that the observed change in litter production results from decreased light availability at the cloud line coupled with lower temperatures with elevation.
Seed germination of seven tree species in three red (660 nm) to far-red (730 nm) light environments were studied in 1995 to determine the germination success of a number of species in different light environments.
|Vegetation dynamics||Seedling and Sapling Dynamics||
Studies of seedlings and saplings are and have been conducted on several landslides and plots on the LEF. The primary purposes are to study seedling recruitment and seedling and sapling growth and the effect of hurricane disturbance (specifically Hugo) on these processes as related to the degree of canopy disturbance, and the temporary reduction in shade from the defoliation of the canopy under distinct soil conditions.
The primary purpose of this study is to look at seedling recruitment, and the growth of seedlings and saplings as it relates to the degree of canopy disturbance caused by Hurricane Hugo. Although all trees down to 1-cm dbh will eventually be identified and measured for the separate 16-ha grid project, the smallest trees will not be measured for at least a year, and seedling will not be included in the 16-ha grid program. The seedling/sapling plots in the 9-ha grid will allow us to follow early responses of seedlings and saplings to increased light. Tree maps for the 16-ha grid which will encompass the 9-ha grid) will eventually be used to determine the proximity of seed-source trees to each plot.
Treefall Pits Study
In this study, I compared seedling and sapling dynamics in soil pits and undisturbed forest floor, were both environment has experienced a temporary reduction in shade from the defoliation of the canopy during Hurricane Hugo (September 1989) but had soil conditions that were distinct. Soil pits were chosen as the microsite within the treefall gap most likely to differ in soil characteristics from the adjacent forest and most likely to alter plant establishment patterns. Soil mounds, important sites of establishment in some temperate forests (Webb 1999), erode quickly under the high rainfall conditions in Puerto Rico and were not considered in this study. I asked the following questions: (1) how does the soil physical environment differ between the soil pit and the forest floor?; (2) do tree species that have N-fixing symbionts influence soil nutrients or species composition of colonizers?, and (3) what are the consequences of uprooting and defoliation for populations of seedlings and saplings and for tree recruitment?
|Ecosystem dynamics||Soil Carbon and Nutrients in the Luquillo Experimental Forest (LEF)||
In this study, we examine the spatial variability of soil carbon, nitrogen and phosphorus in the Luquillo Experimental Forest (LEF) using a spatially explicit version of the CENTURY biogeochemistry model. We took soil samples from 119 locations in the Luquillo Mountain during the summer of 1998 and 1999. Then we compared the simulated soil C, N and P pools with observed values as a way to validate our simulation results.
|Charles A.S. Hall|
|Ecosystem dynamics||Soil Nutrient Dynamics in Bisley||
Soils and forest floor were sampled quantitatively from a montane wet tropical forest in Puerto Rico to determine the spatial variability of soil nutrients, the factors controlling nutrient availability, and the distribution of nutrients in soils and plants following Hurricane Hugo.
|Ecosystem dynamics||Soil Organic Matter Dynamics in Tabonuco Forest||
In this project we try to find out the relationship between the primary production and the soil organic carbon fractions in the tabonuco forest, a plantation and a secondary forest in Guzman.
|Environmental monitoring||Streamflow in the Luquillo Experimental Forest (LEF) Canopy Trimming Experiment||
The US Geological Survey has monitored daily average streamflow (in cubic feet per second; CFS) at 19 streams in or near the Luquillo Experimental Forest starting in 1945 (Table 1). Twelve streams are reported here. This summary includes monthly summaries of that data set through 30 September 1994. More recent data are available from the USGS Streamflow Web site.
|Ecosystem dynamics||STREAMS Project at La Selva Biological Station, Costa Rica||
The STREAMS Project at La Selva Biological Station, Costa Rica (owned and operated by the Organization for Tropical Studies, OTS) was established in 1985. Before this program, little was known about the biogeochemistry, structure, and function of Central American streams. Scientific understanding of neotropical streams has been primarily based on research conducted in South America on the Amazon (and to a lesser extent, the Orinoco). Results of the STREAMS Project comprise one of the few longterm datasets on stream solute chemistry and ecology in primary lowland rainforests of Central America. The project encompasses four areas: (1) linkages between stream ecology and biogeochemistry (e.g., Pringle 1991; Pringle and Triska 1991; Pringle et al. 1993, Triska et al. 1993; Duff et al. 1996; Genereux and Pringle 1997, Pringle and Triska 2000, Triska et al. 2006a,b, Ramirez and Pringle 2006, Ramirez et al. 2006, Stallcup et al. 2006, Ardon and Pringle in press); (2) the trophic dynamics and ecology of stream communities (Pringle and Hamazaki 1997, 1998; Pringle and Ramirez 1998; Ramirez and Pringle 1998; Rosemond et al. 1998; Rosemond et al. 2001, 2002); (3) management applications (Anderson-Olivas et al. 2006); and (4) environmental outreach on water quality and quantity issues (Pringle 1997, 1999). Pringle initiated this project in 1985 through several postdoctoral awards. In 1988, the National Science Foundation (NSF) began funding the project. It has since been funded by five consecutive NSF awards. The project is currently funded by an NSF Long-Term Research in Environmental Biology Award (2006-2011). NSF also provided two supplementary awards for the extension of research at La Selva to the Luquillo LTER site in Puerto Rico.