Year of Graduation

2022

Document Type

Thesis

Major

Environmental Studies

Directing Professor

Dr. Elizabeth Gleim

Abstract

The emerald ash borer (EAB; Agrilus planipennis) is a buprestid beetle native to Asia, classified as an invasive species in North America. EAB infests trees of genus Fraxinus (ash) and has spread to 35 states since its introduction in the early to mid-1990s. Notably, EAB has the potential to functionally extirpate all native ash species in North America. Our study aims to characterize the ecological impacts of EAB infestation in the Roanoke Valley of Southwest Virginia, to quantify the impact of edge effects on EAB forest invasion and mortality of ash trees, as well as investigate the role that forest edge effects play in forest regeneration post-ash tree mortality. In 2017, twelve forested study sites, six with ash trees and six without (e.g. controls), were established in the Roanoke Valley. Data were collected annually through 2020 on tree species composition and growth, as well as understory woody species composition. Signs of EAB infestation and ash mortality were tracked via a dieback scoring system at the ash sites across all study years. Significant increases in dieback scores of large (>12-cm DBH) and small (<12-cm DBH) trees across all years were documented, indicating progressive mortality of ash trees. Large trees had significantly higher dieback scores than small trees indicating more rapid progression of mortality, particularly in 2019 and 2020. Finally, while there were significantly less ash seedlings at the edge of ash sites (8.04 +/- 0.98) than in the core ( 20.20 +/- 2.27), there were no significant changes over time in the mean number of ash seedlings in the edge or core of ash sites. This may be due to harsher microclimatic conditions in the edge leading to lower seed production and/or recruitment. Because percent cover of invasive vine species was significantly higher at the edge of ash sites (14.22 +/- 3.02%) than in the core (6.51 +/- 3.27%), the survival of ash seedlings at the forest edge may be suppressed and thus survival of ash in these forests may be dependent upon the survival of ash seedlings in the core.

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