Ecological restoration of degraded lands, such as abandoned agricultural fields, often requires establishing native species in challenging environmental conditions. The interruption of this process by invasive species poses a significant obstacle to native plant reestablishment. Woody invasive species like Callery pear (Pyrus calleryana) outcompete native plants, creating favorable conditions for invasion and rendering post-agricultural fields unsuitable for native species establishment. Traditional methods for controlling invasive species require consistent upkeep and observation, but in tallgrass prairies, increasing the diversity and abundance of plants has shown some ability to decrease the number of invasive species in the area. In collaboration with community partners at Five Rivers Metroparks, our laboratory initiated an experiment on a 30-acre parcel of post-agricultural land in Trotwood, Ohio. Twenty 50 x 50m plots were established, each receiving one of four prairie seed mixes with varying levels of species diversity and legume content (n = 5 / seed treatment). These plots were further subdivided and treated with one of four soil amendments: mulch, whole soil, mulch & whole soil, and a control with no amendment. In this thesis I describe the findings of my botanical assessment of prairie establishment that was based on a vegetation survey conducted in the summer of 2023. I found that there is still a significantly smaller presence of invasive species compared to native species. The site is comprised of mainly native species (~80%), although this is mainly driven by species that were not seeded on the site. There is also a higher species richness in the higher diversity seed mix plots than the lower diversity seed mix plots, which shows some success in the different seed mixes. There was no correlation in the presence of legumes and the applied seeding treatments or soil amendments, and the legume species were primarily spontaneous species such as Trifolium (open full item for complete abstract)

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 chemistry can reduce the likelihood of native species to establish and can prevent invasive species from establis (open full item for complete abstract)

Ecological invasion is one of the most important processes of global change influencing ecosystems in practically every biome on Earth. Invasive species shift ecosystem dynamics, community structures, nutrient cycling, and ecosystem function. Invasive species pose a significant challenge to land managers who are charged with maintaining biodiversity and managing long-term ecosystem structure. Pyrus calleryana is an ornamental tree species that escaped cultivation and grows rapidly in highly disturbed soils with high light intensities. Former agricultural fields are highly susceptible to invasion from Pyrus calleryana. Observational evidence suggests that two features of this species' biology may be particularly important to invasion success: (a) an extended leaf phenology and (b) the ability to persist in grasslands following disturbance via epicormic sprouting. While this tree is one of the most problematic invasive species within the Eastern and Central parts of the United States, it is relatively understudied. This thesis is divided into two distinct studies that address the invasion biology of Pyrus calleryana. The first study, detailed in Chapter One, is an analysis of the timing of leaf development (phenology) in relationship to co-occurring native trees. In the second study, detailed in Chapter Two, I conducted a replicated field experiment to assess P. calleryana sprouting as a mechanism of persistence in response to experimental disturbance treatments including prescribed fire and experimental freezing using a treatment of liquid nitrogen. The experiments we conducted in this project are in cooperation with the conservation staff at the Five Rivers Metroparks and all activities took place on their properties. In the first study, I discovered that P. calleryana has a longer leaf duration than native trees through earlier leaf out, and delayed abscission. In addition, a late season frost event allowed for a serendipitous study that revealed much greater frost (open full item for complete abstract)

Pyrus calleryana is an emerging invasive species that appears to have had a recent and rapid increase in the rate of population spread. The species is a very popular ornamental tree, with as many as 29 different cultivated varieties. The species was originally thought to be of little invasive potential due to its genetically-controlled self-incompatibility mechanism and clonal propagation methods, so that cultivars were essentially clones of the same source tree. Virtually unknown as an invasive ten years ago, naturalized populations have since been identified in 26 states. Genetic analyses show that cultivars are highly genetically structured and are polymorphic at the self-incompatibility locus. Invasive trees were also highly admixed hybrid progeny of these different cultivars. In cross-pollination experiments, all cultivars were capable of freely crossing, indicating all are functionally different at the self-incompatibility locus. Measures of reproductive and establishment ability were used to compare different cultivars and hybrid types in terms of an advantage in contribution to invasive populations. All groups were found to be highly fecund, have low mortality, and have high biomass accumulation. Invasive trees also produced greater numbers of seeds than cultivated individuals, indicating that invasive populations may have an increasing rate of spread due to high reproductive output. Cultivated populations, therefore, appear to be the source for invasive populations, and invasive populations are self-sustaining and composed of highly productive individuals. In the case of the Callery pear, availability of multiple cultivar types and widespread horticultural use seems to have allowed the species to not only naturalize, but also increase reproductive output.