Effects of forest features and location on emerald ash borer (Agrilus planipennis) infestation severity of ash (Fraxinus spp.) trees

Abstract

The Emerald Ash Borer (Agrilus planipennis; EAB) is a well-studied invasive species that was first discovered in the United States in 2002 (Herms and McCullough, 2014), and has spread quickly since, infesting all ash (Fraxinus sp .) trees native to the U.S (Cappaert et al., 2005). Once symptoms are observed, infested trees die within 3-4 years (Herms and McCullough, 2014). Difficulty in detecting new infestations has made them dffficult to contain. EAB prefers Fraxinus spp. stems grown individually in sunlight (Chen and Poland, 2009). Previous studies have also shown that lakes can act as barriers restricting insect pest dispersal (Kim and McPheron,1993). Additionally, there are conflicting results in previous literature regarding Fraxinus spp. density and EAB 's rate of infestation (Krlight et al., 2013; Chen et al., 2009). In order to further investigate these variables' effects on infestation, we considered three questions: ( 1) Does the density of surrounding Fraxinus spp. stems affect the severity of an individual's EAB infestation; (2) Does the distance between a Fraxinus spp. stem and the shoreline affect the severity of its EAB infestation; (3) Does the level of canopy cover surrounding an individual Fraxinus spp. stem affect the severity of its EAB infestation? We created three transects on the University of Michigan's Biological Station (UMBS) property. In each transect we recorded canopy cover, density, and severity of infestation for each Fraxinus spp. stem. Distance to shoreline and density were mapped in ArcGIS. The three Fraxinus spp. found in northern Michigan, F. americana, F. nigra., and F. pennsylvanica are all affected by EAB equally (Agiuset al., 2005), therefore differentiation by species was deemed irrelevant to this study. We found a significant inverse correlation with a weak R2 value between Fraxinus spp. stem density and severity of infestation on individual stems. Our data support the hypothesis that increased Fraxinus spp. density within a stand is associated with slower mortality due to EAB infestation. We found no significant correlation between EAB infestation severity and canopy cover or distance to shoreline. In forest stands, the canopy cover of each stem does not affect whether or not it suffers more severe infestati6ns. We hypothesize that Douglas and Burt Lakes are either not significant barriers to the spread of EAB, or that they are no longer effective barriers.