|LUQ Research Categories||Project Title||Project Description or Abstract||Investigators|
|Ecosystem dynamics||Nutrient Cycling in Tabonuco Forest||
Nutrient Cycling in Tabonuco Forest (MRCE/LTER Litterfall Nutrient Fluxes, and Extractable Soil versus Microbial Biomass Nitrogen)
PROJECT DESCRIPTION: Understanding the long-term impact of deforestation on ecosystem structure and function of tropical forests may aid in designing future conservation programs to preserve biodiversity and sustain ecosystem productivity. We examined forest structure, tree species composition, litterfall (fine and coarse) due to Hurricane Hugo and subsequent fine annual litterfall inputs, litterfall rate, and leaf litter decomposition. The experiment was initiated by the MRCE (Minortity Research Centers of Excellence) program, and continued by the LTER. In addition to measuring nutrient fluxes from litterfall and decomposition, we measured KCl-extractable soil nitrogen in ammonium and nitrate forms to determine the effects of complete fertilization and removal of hurricane debris.
History of litterfall, decomposition and soil nitrogen availability studies (MRCE experiment) at the Luquillo Experimental Forest (LEF):
The Minority Research Centers of Excellence (MRCE) experiment was designed originally to determine whether forest productivity was limited by nutrient availability, genetic constraints or climatic variables along a steep environmental gradient in the Luquillo Mountains of Puerto Rico. Comparisons were made between dwarf forest at 500 m elev. and tabonuco forest from 300-400 m elev. There were two main experiments in the original design: 1) forest fertilization (complete versus none); 2) transplant experiments using common gardens at high and low elevation, with and without wind protection at high elevation. In addition, phenology of leaves was studied in the dwarf forest to determine the longevity of leaves in the canopy.
Hurricane Hugo struck in September 1989, following a year of pre-treatment measurements and just as the forest plot fertilization experiments were to begin, and deposited a year and a half of annual above ground litter inputs of phosphorus on the forest floor in green leaf litter (Lodge et al. 1991). As phosphorus is thought to be the most limiting element, this necessitated the addition of a hurricane debris-removal treatment as a second type of control in the lower elevation tabonuco forest. Furthermore, the hurricane changed the nature of the study into one of looking at changes in forest composition and the recovery of forest productivity in response to fertilization and hurricane debris-removal. Seedling, sapling, herbaceous plant, and fern responses, as well as measurements of light availability and canopy closure were added to the originally planned measurements of tree diameter growth, leaf litter production, and fine root production and turnover. Funding for continued studies of the MRCE plots ended in 1998, but they were of such great value as a long-term experiment that they were incorporated into the LTER program. Another hurricane in 1998 (Hurricane Georges) presented an opportunity to look at the effects of removing only the woody debris (in new plots) versus removing all hurricane debris.
The leaf decomposition experiment was originally designed to examine short-term disappearance of foliage from three important montane species: Prestoea montana (R. Grah.) Nichols, Dacryodes excelsa (Vahl.), and Cyrilla racemiflora. Hurricane Hugo (August, 1989) provided a unique opportunity to study effects of this type of natural disturbance on decomposition. The study was repeated in 1990 as part of the LTER, with some changes in the design that allowed for comparisons of short -term foliar litter biomass and nitrogen dynamics: (1) among the three species, (between the colorado and tabonuco forest types, (3) between riparian and upland sites, and (4) between pre- and post-hurricane environments.
|Vegetation dynamics||Flooded forest plot sampling in the Amazon||
Sampling of plots in three major forest types that differed by flooding duration after 4 years of regeneration showed: (1) common species exist between wet forests and their gaps and between wet and very wet gaps, (2) tree richness is maximum in dry forest and minimum in very wet gaps except in the wet gaps that show the second highest number of species, (3) there were less stems in gaps compared to forests and less stems in forests as flooding increased, except again in the wet gaps, and (4) dominance-diversity curves have more dominance by single species in the dry gap plots compared to other gaps and in dry forest compared to other forests. In general while some aspects of structure such as tree stem density is largely determined by tree-fall gap dynamics, tree composition is determined by flooding regime. Finally a jump in tree richness in wet forests and wet gaps compared to other plots suggests a “mass effects” hypothesis where species from dry and very wet forest and gaps have overlapping ranges in the wet forest and gap. This effect may help explain the high species diversity seen in this part of the Amazon
|Randall W. Myster|
|Environmental monitoring||Meteorology and Hydrology at Bisley||
Several meteorological parameters are being measured at Bisley since 1993. Correlations
Rainfall and Stream-runoff
Long-term rainfall and discharge data from the Luquillo Experimental Forest
Using eqn. (1) to estimate total watershed throughfall becomes a problem of determining the minimum number of vegetation types necessary to describe the system at the required level of accuracy. In one of our studies, measured throughfall was compared with actual canopy and stem conditions to estimate the percentages of throughfall for different time periods was calculated by weighting the average throughfall and stemflow measured in representative areas of each vegetation type by the total area of that vegetation group.
Air and Soil Temperature
The relationship between mean air temperature and elevation is a required parameter
(2) Mean Air Temperature (in C) = 26.4 -(0.00558 * elevation in meters) and
(3) Mean Soil Temperature (in C) = 25.6 - (0.00543 * elevation in meters)
best fit these relationships. The equation that best fits the mean soil temperature
|Animal population dynamics||Differential Abundance of Microbial Functional Groups along the Elevation Gradient from the Coast to the Luquillo Mountains||
Soil fungal communities respond to multiple abiotic and biotic factors that change along elevation gradients. This study documents changes in fungal and bacterial diversity, and abundance and composition of microbial functional groups along a subtropical elevation gradient. The elevation gradient is located in eastern Puerto Rico and is composed of five forest types each with characteristic vegetation. Soil samples were collected every three months from March 2003 thru March 2005. Soil fungal and bacterial communities were analyzed using fatty acid methyl esters (FAME) and TRFLP profiles. Diversity in this elevation gradient is higher at mid-elevations. Most G negative and G positive bacterial FAME were positively related to soil pH in MLR models, lower pH in mid-elevation forest soil may suppress bacteria favoring fungi. These data can be used as a benchmark for monitoring changes in microbial communities along elevation gradients caused by natural and anthropogenic disturbances, as well as global and regional climate changes.
|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.
|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?
|Food web dynamics||Fresh Water Biannual Monitoring||
The LTER is conducting annual monitoring of Algae, Chlorophyll a, benthic organic matter, and benthic inorganic matter in order to document baseline stream characteristics. These data may be used to examine effects of disturbances such as hurricanes on stream ecosystems.
|Vegetation dynamics||Luquillo Forest Dynamics Plot (LFDP)||
The processes that determine the plant species diversity and structure of tropical forest are still uncertain despite many years of investigation. A tropical forest characteristically has few common species and many rare species, with conspecifics often widely distributed throughout the forest. The potential for inter and intra-specific interactions are numerous, and it is difficult to determine which factors maintain species diversity or how rare species survive in the population. Factors that we believe contribute to tropical forest structure and composition include the physical environment and past history of the forest, species-specific physiological requirements for light, nutrients and water necessary for growth, survival and reproduction, and pathogens and herbivores. Despite the substantial amount of information available about these factors, we are still unable to accurately model the current composition of tropical forest or to predict its future response to human and natural disturbances.
The Luquillo Forest Dynamics Plot (LFDP), previously known as the Hurricane Recovery Plot (Zimmerman et. al. 1994) and the Luquillo long-term ecological research grid (Soil Survey 1995), is a 16-ha forest plot (SW corner 18° 20' N, 65° 49' W) located near El Verde Field Station. The plot is 500 m N-S and 320 m E-W and is divided into 400 20 x 20 m quadrats, with each quadrat sub divided into 16 5 x 5 m sub-quadrats. The field station and LFDP are in the Luquillo Mountains of northeastern Puerto Rico, approximately 35 km southeast of San Juan. Information from the LFDP contributes to the efforts of the Center for Tropical Forest Science (CTFS, Smithsonian) network of large tropical forest plots in order to improve our understanding of tropical forest and to predict its future. Large plots (typically 50 ha) are required to cover local environmental variation, include sufficient numbers of individuals of both the common and rare species, and to determine plant spatial relationships. Population monitoring is required over many years to elucidate tree life histories, species interactions and population changes in order to determine the forest response to environmental changes and disturbance.
The LFDP is unique among the CTFS sites as it has a history of land use disturbance and also hurricane damage. These two disturbance types interact and influence the community dynamics and species composition in the LFDP. The Northern area (approximately two thirds of the plot) was disturbed by tree felling and farming until 1934 when the land was purchased by United States Department of Agriculture, Forest Service. The Southern third was not farmed and only suffered relatively light disturbance from selective logging. Aerial photographs taken in 1936 show differences in canopy cover caused by the patterns of land use history. Clear patterns in the distribution of some species reflect this land use history (Thompson et. al. in press). . The distribution of species as a result of the land use history interacts with hurricane disturbance, as those species colonizing the northern part of the LFDP are more susceptible to hurricane damage (Zimmerman et. al. 1994). Major hurricanes struck the forest area of the LFDP in 1928 and 1932 and after a 66 year period with relatively little hurricane damage, the forest was struck by Hurricane Hugo struck in 1998 and Hurricane Georges in 1989, both hurricanes causing significant damage.
|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
|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.