A nitrogen budget for late-successional hillslope tabonuco forest, Puerto Rico

A Nitrogen Budget for Late-Successional Hillslope Tabonuco Forest, Puerto Rico
Tamara J. Chestnut, Daniel J. Zarin, William H. McDowell and Michael Keller
Vol. 46, No. 1/3, New Perspectives on Nitrogen Recycling in the Temperate and Tropical Americas (Jul., 1999), pp. 85-108

Nitrogen budgets of late successional forested stands and watersheds provide baseline data against which the effects of small- and large-scale disturbances may be measured. Using previously published data and supplemental new data on gaseous N loss, we construct a N budget for hillslope tabonuco forest (HTF) stands in Puerto Rico. HTF stands are subject to frequent hurricanes and landslides; here, we focus on N fluxes in the late phase of inter-disturbance forest development. N inputs from atmospheric deposition (4-6 kg N/ha/yr) are exceeded by N outputs from groundwater, gaseous N loss, and particulate N loss (6.3-15.7 kg N/ha/yr). Late-successional HTF stands also sequester N in their aggrading biomass (8 kg N/ha/yr), creating a total budget imbalance of 8.3-19.7 kg N/ha/yr. We surmise that this imbalance may be accounted for by unmeasured inputs from above- and belowground N-fixation and/or slow depletion of the large N pool in soil organic matter. Spatial and temporal variability, especially that associated with gaseous exchange and soil organic matter N-mineralization, constrain the reliability of this N budget.