Impacts of the Invasive Emerald Ash Borer on Ash Tree Physiology and Forest Ecology

Invasive species are widely recognized as altering species and community dynamics, but their impacts on biogeochemical cycling and ecosystem processes are less understood. I investigated the impacts of the emerald ash borer (Agrilus planipennis Fairmaire, EAB), a phloem feeding beetle that was inadvertently introduced to the US in the 1990’s, on ash tree physiology and forest ecosystem dynamics.;I assessed the physiologically basis for the visual canopy decline classes used by managers to rapidly assess EAB induced tree decline in the field. I found that EAB will impact health and physiologically stressed trees. The abundance and damage increases as the tree canopies declines. Furthermore, I found a significant relationship with foliar 13C and gallery cover indicating that the physiological basis of EAB induced tree decline is larval feeding which inhibits water transport. Building of the finding that EAB larval galleries impact water transport, I investigated tree-level water use in ash trees experiencing different degrees of EAB damage. I found that EAB significantly reduces daily tree-level water use by upwards of 80%. I also found evidence supporting abiotic drivers of water use.;I investigated the potential impacts of EAB on standing C stocks in forests of the US, by using the forest inventory and analysis database. I found that forests in the Midwestern US will experience the greatest impacts from EAB, as they contain significant quantities of ash trees, between 5-9% in the Great Lakes Region. To investigate ecosystem responses, I tracked tree growth and decline in forests in EAB impacted and non-EAB impacted regions. Using data on the growth rates of trees in the non-EAB impacted regions, I modeled the impacts of EAB on impacted ash forests. I found that EAB reduced forest net ecosystem production by ∼31%, and that there was a considerable compensatory growth of non ash trees which reduced the severity of this disturbance. I found that maple and elm trees responded most positively. This study illustrates the ecosystem and regional scale impacts of invasive pest-induced disturbance on biogeochemical cycling and forest species composition.;Following up on this, I experimentally manipulated an ash forest to low, moderate, and high EAB levels to measure responses in tree growth, canopy decline, soil respiration and foliar 13C. I found that the medium and high EAB treatments reduced net ecosystem production, canopy openness, and soil respiration. Foliar 13C signatures indicated a release from water competition associated with the decline in ash trees in the moderate and high EAB treatments. This study highlighted the impacts of forest pests on above and belowground feedbacks.;Finally, by combining observational and destructive tree harvesting approaches, I assessed woodpecker predation on EAB larvae in a deciduous forest in central Ohio. Results indicate that woodpeckers selectively forage more heavily on ash trees than nonash trees (87 v 7 %), and that they forage preferentially on ash trees that exhibit canopy decline symptoms relative those with healthy canopies. These patterns were largely supported by the destructive sampling of ash trees and indicate that woodpecker predation can significantly reduce tree-level EAB densities by upwards of 85%. Our results suggest that woodpeckers may use visual canopy decline, and perhaps other cues, to target ash trees with greater stages of EAB infestation. Moreover, our results provide insight into the indirect effects of invasive species on biotic interactions in forest ecosystems and highlight potential shifts in woodpecker foraging behavior in response to a novel forest pest. Woodpeckers respond to EAB infestation and may thus potentially help regulate EAB populations and their spread in a mixed deciduous forest.