Catastrophic Disturbance in a Tropical Rain Forest - Impact of the Riparian Zone on Nutrient Export

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On September 17-18, 1989, Hurricane Hugo almost completely deforested portions of the Luquillo Experimental Forest in Puerto Rico. Hurricane deforestation differs substantially from other disturbances that have been studied in tropical forests (logging, slash and burn agriculture) principally in that an enormous amount of live biomass instantly enters the surface litter compartment. Insufficient data exist to predict how this litter input will affect or be affected by nutrient dynamics in the riparian zone of this tropical forest. Drs. McDowell, Bowden and Smith have been sampling near- surface ground water and stream water at two sites in this forest since August 1988. Their work emphasizes the nutrient and water flux through the riparian zone and assesses the relative importance of microbial versus vascular plant control of nutrient flux through this interface. This new project will examine the impact of deforestation caused by Hurricane Hugo on the ability of riparian zones to regulate transport of nutrients from terrestrial to aquatic ecosystems. The investigators hypothesize that the riparian zone plays a crucial role in regulating losses of nitrogen following this catastrophic disturbance. They specifically identify two major hypotheses: 1) deforestation associated with Hurricane Hugo will result in increased fluvial export of nitrogen from the Bisley watershed, and 2) the magnitude of nitrogen export in stream water will be lessened significantly by nitrogen retention and transformation. To test these hypotheses, information from before and after Hurricane Hugo will be compared at two sites, one disturbed and one undisturbed. The scientists engaged in this research are experienced, productive researchers who have previous experience with riparian processes in tropical forests. The program is supported by excellent institutional facilities.