Determining Change in Coastal Barrier Island Dune Vegetation Following a Decade of Nitrogen Fertilization

Nitrogen deposition from agricultural and industrial sources is a threat to terrestrial biodiversity, and impacts are likely to be greatest in nitrogen-deficient systems. The results of a 10 year fertilization treatment on nitrogen-deficient coastal barrier island dunes and the decade following cessation of fertilizer application are reported here. The study objective was to determine the resilience of the dune plant communities. Would these communities return to their former state in terms of density, species composition, and species diversity after nitrogen additions ended, and if so, how rapid was their recovery? Plant density by species and species diversity were determined over a 20 year period from permanent plots established on three different-aged dunes on a Virginia barrier island. Two dominant species responded differently to nitrogen additions. Ammophila breviligulata abundance was enhanced by the additions, and, in most cases, Spartina patens abundance was repressed. On the older Hog Island dunes, the addition of nitrogen over a 10 year period had a dramatic and rapid negative effect on diversity. However, recovery to diversity values observed in the control plots was rapid, beginning almost immediately after nitrogen additions were stopped. The dune vegetation on a Virginia barrier island appears to be quite resilient, as it rapidly recovered from diversity loss after 10 years of nitrogen additions.