Restoring Degraded and Invaded Landscapes

Date of Award


Degree Name

Ph.D. in Biology


Department of Biology


Ryan W. McEwan


Ecosystem disturbance and degradation have led to dramatically altered plant communities, necessitating their restoration to return to native states. One disturbance is emerald ash borer, an exotic, invasive insect that has decimated ash tree populations creating gaps in many forest canopies. Due to the influx of exotic invasive plant species, traditional forest recovery has been altered in that plant species establishing in gaps favor invasive shrubs to native tree seedlings. Thus, I measured the growth and survival of native tree species planted within a forest affected by emerald ash borer to determine what species may outcompete invasive species and regenerate into the forest canopy. I found that butternut and shellbark hickory trees had high survival rates compared to red oak, and could be target species for replacing ash trees in stands impacted by emerald ash borer. When fallow fields are dominated by Callery pear, a pervasive new invader in the Eastern US, native plant establishment may be limited. I found that Callery pear tends to invade near forested edges of grassland ecosystems, likely because there is increased propagule pressure from generalist frugivorous birds which forage both in Callery pear invaded areas and on forest edges creating seed rain. Callery pear occurs where there is less ground cover of forbs and grasses suggesting that it either invades in areas that have less plant cover or that it inhibits the establishment of native species. In a lab-based experiment, I found that Callery pear is likely allelopathic and can inhibit the germination of common prairie species which could prevent its establishment. Further, in the field, I found that Callery pear can acidify the soil where it establishes, and it may input carbon into the soil system which changes the activities of microorganisms in the soil. Together, these changes to soil Department of Chemistry can reduce the likelihood of native species to establish and can prevent invasive species from establishing, potentially lending to the creation of dense monocultures where this tree invades. Another disturbance to many ecosystems is industrial agriculture, which has degraded native ecosystems reducing soil organic matter content, water holding capacity and altering Department of Chemistry. During traditional succession in the Eastern US deciduous ecosystems, native plant cover would regenerate with time in open fields and forest canopies could develop within 50-100 years of passive regeneration. The first plants to establish during succession have long distance dispersal mechanisms and can survive harsh environments with little plant cover and eroded soils. When assessing the change in soil Department of Chemistry from 0-to 100-year-old forests regenerated on previous agricultural fields, we identified a recovery in soil carbon, nitrogen and water capacity, which increased the growth of bur oak seedlings when grown in a greenhouse environment, indicating that restoring soils could promote the regeneration of oak species. To accelerate the process of forest restoration informed by this study, I implemented soil amendments and planted transitional prairie communities to increase native biodiversity and resist invasion in a fallow agricultural field, which led to the initiation of a long-term research and forest restoration site, outlined here.


Biology, Ecology, Pyrus calleryana, restoration, oak, Quercus, soil enzyme, invasion, Callery pear

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