Tuesday, August 7, 2007 - 2:50 PMCOS 52-5: Effects of invasive beach grasses on the shape and composition of coastal dunes
Phoebe L. Zarnetske, Eric Seabloom, and Sally D. Hacker. Oregon State University
Coastal dune communities harbor many rare and endangered species and also protect coastal communities from high waves and flooding. The biodiversity and coastal protection services provided by these dunes are strongly influenced by the combination of biotic and abiotic forces. Over the last century, North American West Coast dunes have changed dramatically due to the intentional planting of two non-native beach grass species, Ammophila arenaria and A. breviligulata. Currently, Ammophila dominates nearly all of the dune systems on the West Coast. Through their sand-binding abilities, these ecosystem engineers have created large continuous foredunes, which stabilize sand, promote wetland and forest encroachment, and alter the ecosystem trajectory. Using long term survey data, we show that A. breviligulata has rapidly displaced A. arenaria throughout Washington and northern Oregon , and is potentially lowering dune heights where it dominates the foredune vegetation. Of particular importance to coastal dune community states and coastal protection is the prediction of how continued spread of A. breviligulata will alter dune geometry, and the susceptibility of foredunes to overtopping and breaching from high waves and water levels, especially in light of future climate change predictions (i.e., intensified storms and sea level rise). We also demonstrate the corresponding decline in native species diversity arising from this invasion.