Nutrient Cycling in Tabonuco Forest related data sets

PROJECT TITLE: 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.