Effect of an Introduced Ambrosia Beetle (Xyleborus glabratus) on Red Bay (Persea borbonia) Mortality in Maritime Forest Communities of St. Catherine's Island, GA

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Hess, Matthew
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barrier island , red bay , pathogen , American chestnut , American elm , St. Catherine's Island
Over the past three years, red bay (Persea borbonia, Lauraceae) populations along the Georgia coast have experienced high levels of mortality due to an introduced fungal pathogen (Ophiostoma sp.) being spread by outbreaks of a recently introduced, Asian ambrosia beetle, Xyleborus glabratus. The beetle carrying the fungus was believed to have arrived in this country on shipping pallets and was first identified in the port of Savannah, Georgia in 2002. Red bay is an abundant and ecologically important tree species found in the coastal plain of the southeastern United States. This study represents the first assessment of red bay decline, which as a casualty of an introduced pathogen, may be following the same fate as American chestnut, American elm and flowering dogwood in the forests of the eastern U.S. Five 5000m2 plots were established on St. Catherine’s Island, a barrier island south of Savannah. The status of red bay populations in these plots was assessed in 2004, 2005 and 2006 for leaf wilt, diameter at breast height (DBH), and the presence of basal sprouts. It was determined from that red bay is a common species represented in many size classes. Across the five study sites, the proportion of fully wilted red bays increased from 0.06 in 2004 to 0.89 in 2006. A fitted logistic regression model for binary response variables suggested that DBH was not a significant predictor of probability of infection (p>0.05), while site and year were significant (p<0.05). The odds of basal sprouting on a dead tree in 2006 were 7.09 times higher than the odds of sprouting on a live tree. However, potential regeneration by basal sprouts was severely limited by deer browse. A comparison with Dutch Elm Disease (DED) and other significant tree losses suggest that red bay will likely meet the same fate. This will have serious consequences for the already degraded maritime forest ecosystem in terms of species composition, structure and function.