Redbay (Persea borbonia) abundance and the potential effect of Laurel Wilt Disease in the Bald Head Woods Reserve, North Carolina, USA Maureen E. Dewire Department of Environmental Studies, University of North Carolina at Wilmington Submitted in partial fulfillment of Masters of Arts Degree May 2011 ! "! Table of Contents Abstract………………………………………………………………………………3 Introduction…………………………………………………………………………..3 Methods………………………………………………………………………………9 Results………………………………………………………………………………...10 Discussion…………………………………………………………………………….11 Figures and Tables…………………………………………………………………....14 Map of P. borbonia and LWD Distribution………………………………….14 Map of Study Site…………………………………………………………….15 Graphs of P. borbonia Percent Cover in BHI Woods………………………..16 Tables of Transects 1-5………………………………………………………17-18 Works Cited…………………………………………………………………………..19 ! #! Abstract Laurel Wilt Disease (LWD) has spread rapidly across the southeastern United States since first identified in Georgia in 2004, causing significant mortality of redbay (Persea borbonia) in the coastal plain. Vectored by the invasive redbay ambrosia beetle (Xlyeborus glabratus), LWD is a fungal disease (Raffaelea lauricola) that causes near 100% mortality in infected areas with no effective methods of control identified to date. Aided by anthropogenic actions, LWD is now established in North Carolina, South Carolina, Georgia, Florida and Mississippi. Bald Head Woods Reserve, located on Bald Head Island, North Carolina, is a 191-acre preserve of maritime forest at risk of losing its redbay population should LWD expand to the island. Maritime forests are globally imperiled ecosystems that are generally not well understood. Further, there is even less known about how forest compositions will be altered by the removal of redbay from the system. This study sought to identify the percent cover of redbay in Bald Head Woods in anticipation of the imminent arrival of LWD. Examination of 52 quadrats along five transects within the reserve boundary lines found that approximately 11.4% of the plant cover in the Bald Head Woods is redbay with the majority occurring in the southern portion of the forest. Future monitoring of the current redbay population will be essential to better understanding the impacts of LWD. It is suggested that the current redbay population be categorized by size and closely monitored for LWD infection. If and when LWD impacts Bald Head Woods, it will be important to study the rate of death, the size class affected, changes in forest species composition and signs of successful regeneration. Introduction Maritime forest communities can be found along the eastern seaboard of the United States, stretching from North Carolina south to Florida, restricted to barrier islands and the adjacent mainland (Bellis, 1995). Defined by the North Carolina Coastal Resources Commission as “those woodlands that have developed under the influence of salt spray on barrier islands and estuarine shorelines”, maritime forest are influenced by several environmental factors: exposure to high levels of salt; strong winds and tidal overwash during storm events; poor nutrient levels in the soil; limited supply of freshwater; unstable soil that is prone to wind or water erosion (Bellis, 1995). There are several distinct but related communities within this coastal zone, defined by ! $! their species composition and physical characteristics (Schafale and Weakley, 1990). Specifically, maritime evergreen forests are located on barrier islands, formed on old sand dunes that are out of the reach of storm surge flooding and away from the most intense salt spray. They differ from other coastal zone communities (maritime deciduous forest, maritime shrub and coastal fringe evergreen) by the presence of hardwoods in the canopy (Q. virginiana and Q. hemispaerica), a tree canopy height of greater than 5m tall, and their limited distribution on barrier islands or the ocean side peninsulas, respectively (Schafale and Weakley, 1990). Although somewhat protected, maritime evergreen forests must cope with a series of stresses including a constant salt spray and disturbance from storm events including hurricanes (Schafale and Weakley, 1990). This community is distinguished from the maritime deciduous forest by the presence of live oak (Quercus virginiana) and laurel oak (Quercus hemisphaerica) as the dominant canopy trees (Bellis, 1995). The Smith Island Complex in southeastern North Carolina is a southern variant of this forest, with Sabal palmetto (Sabal palmetto) an additional member of the forest canopy (Bellis, 1995). Together, these trees provide a network of limbs and foliage that create a canopy, thereby protecting the understory trees, shrubs and vines that include red cedar (Juniperus virginiana), yaupon holly (Ilex vomitoria), Carolina laurel cherry (Prunus caroliniana), redbay (Persea borbonia), flowering dogwood (Cornus florida), wax myrtle (Myrica cerifera), wild olive (Osmanthus americanus), American beautyberry (Callicarpa americana), muscadine grape (Vitis rotundifolia), poison ivy (Toxicodendron radicans) and Smilax spp (Bellis, 1995). Considered globally imperiled ecosystems, maritime forests are a critical component to the overall health and stability of barrier islands providing habitat and foraging material for wildlife, stabilizing the soil and acting as a buffer against severe storms. These features also make ! %! maritime forests attractive for development and many have been partially or fully removed to make room for homes and buildings, an action likely to have long-term negative impacts on the health of such forests (Schafale and Weakley, 1990). Habitat fragmentation and the loss of biological and ecological functions as a result of development is one of the greatest challenges facing maritime forests (Bellis, 1995). A more recent threat to the health of maritime forests is the introduction of non-native, invasive species that have the potential to wreak havoc on entire ecosystems. Due in large part to the expansion of global trade, the unintentional introduction of harmful species has increased significantly in recent years (Liebhold et al. 1995). Pimentel et al. estimate an astonishing 50,000 non-native species now occur in the United States with some brought in intentionally, others by accident (2000). While not all introduced species will become established and some are even beneficial, a lack of natural predators outside their normal range allows exotics to rapidly overrun their native counterparts, resulting in the potential for catastrophic losses, both ecologically and economically (Pimental et al. 2000). Invasive species are considered one of the leading causes of biodiversity loss; 49% of imperiled species are in decline in large part due to non-native species, according to federal agencies and The Nature Conservancy (Wilcove et al. 1998). Two of the greatest threats to the health of forests in the United States are the introduction of insects and pathogens. Familiar examples include the chestnut blight fungus (Cryphonectria parasitica) and the hemlock woolly adelgid (Adelges tsugae), both infestations resulting in massive alterations in forests and species composition across the northeastern United States (Spiegel, 2005). In the past decade, a newly introduced species, the redbay ambrosia beetle (Xyleborus glabratus), has established itself across the coastal plain of the southeastern United States. The ! &! 2mm-long beetle vectors a non-native fungus (Raffaelea lauricola), resulting in widespread mortality of redbay (Persea borbonia) trees and other members of the Lauraceae family, including sassafras and avocado (Fraedrich et al. 2008). First discovered in 2002 near Georgia’s largest shipping port in Savannah, it is assumed that X. glabratus, an ambrosia beetle native to Asia, arrived via cargo ships and wood packing material (Fraedrich et al. 2008). By 2003 and 2004, significant mortality events of redbay trees were being documented in the coastal regions of both Georgia and South Carolina, though the exact cause was not determined until late 2004 by which time eradication was deemed unfeasible (USDA, 2010). Inspection of the dead trees resulted in the discovery of several species of ambrosia beetles, some native, some exotic. One native ambrosia beetle, the black twig borer (Xylosandrus compactus) is known to cause damage to small diameter branches on redbay trees, mimicking the initial damage caused by X. glabratus; the twig borer however does not impact larger limbs or kill the entire tree as X. glabratus does (USDA, 2010). Like most ambrosia beetle species, adult X. glabratus bore into healthy trees, creating tunnels in which they lay their eggs. As part of a symbiotic relationship, the beetle carries a fungus in its mycangia that is released into the tree and serves as food for the developing larvae (Fraedrich et al. 2008). This fungus, R. lauricola, spreads through the vascular tissue of the tree, prohibiting the uptake of nutrients and water, resulting in the ‘wilt’ appearance and eventual death of the tree, hence the name Laurel Wilt Disease (LWD) (Fraedrich et al. 2008). In an experiment carried out by Fraedrich et al., R. lauricola was found regularly inside the head of X. glabratus confirming their symbiotic relationship (2008). Further in their experiment, they found that when X. glabratus were exposed to redbay trees, 96% of the trees were bored into by the beetles, 70% of the trees died, and R. lauricola was present in 91% (Fraedrich, 2008). Results from these experiments