Human land uses, including the expansion of urban areas, threaten biodiversity globally by damaging natural ecosystems and disrupting their functioning. Ecological restoration, or the process of assisting the recovery of an ecosystem that has been damaged or destroyed, has the potential to halt or reverse biodiversity loss due to urban expansion. Unfortunately, the outcomes of ecological restoration are often variable and unpredictable, and typically fall short of achieving the same levels of biodiversity and functioning as ecosystems which have not been impacted by human land uses. In this dissertation, I conducted a research program to identify and describe the drivers of variation among ecological restoration efforts within urban areas using a common plant community – prairies – a once abundant and now largely lost native plant community in the Midwestern U.S.A across each study.Much of what we know about the factors that impact the outcomes of ecological restoration efforts is largely from work done in non-urban areas. To address this research gap, I developed two studies which work together to identify the factors that impact the outcomes of ecological restoration efforts in urban areas. The first was an observational study across previously established prairie restoration planting sites to identify how the plant communities within each site were impacted by factors that are often altered by urban expansion, such as the environmental site conditions and amount of urban land cover surrounding the planting sites, as well as restoration practices. This study revealed that variation in plant community composition among restoration plantings was related primarily to site-level factors, such as soil and local climate conditions, rather than the surrounding landscape context. I found that non-prairie species increased in richness in response to warmer local climate conditions but decreased in richness in response to soil conditions that had elevated water holding capacity, were less compacted, or sandier. Prairie species richness responded oppositely to these factors. The second study examined how the plant communities are impacted by factors that are often altered by urban expansion when restoration practices are tightly controlled across newly established prairie restoration plantings in the Lansing, Michigan (USA) metro area. Factors that impact the arrival and establishment of prairie species within a restoration planting site may be different from those acting on already established prairie plant communities. Thus, the identification of factors which limit or enhance the success of establishment will enable restoration practitioners to improve restoration success. This study revealed that both local site conditions as well as the amount of urban land cover in the surrounding landscape impacted plant community establishment, but like the previous study, prairie and non-prairie species responded to these factors differently. Prairie species richness and occurrence was consistently lower with increasing amount of surrounding urban land cover, whereas non-seeded species were largely shaped instead by environmental site conditions. Both studies indicate that restoration practices developed in non-urban areas can and should be extended to urban areas to better understand the impact of environmental site conditions and landscape context on plant community development, and that prairie plant communities are good candidates for this work. Urban ecosystems face novel environmental conditions due to human land uses; one such challenge is roads and salt addition for winter road management. In my third chapter, I designed a study to test the impact of road salt deposition on newly established prairie plant communities to better understand how this novel environmental stressor impacts plant community assembly. Additionally, we tested the effects of road salt deposition on species sourced from both the Midwest and coastal populations of some prairie species as it is likely that ability to tolerate roadside salt deposition likely differs across and within species due to natural adaptations to saline conditions. There were clear effects of salt deposition on the seeded prairie plant species. Although prairie plant species were able to establish at all levels of salt deposition, even low levels of salt deposition had negative impacts which magnified at intermediate to high levels of salt deposition. These effects were not mitigated by sourcing seed from coastal populations. Together, my findings illustrate that many of the same drivers of variation in non-urban systems are similarly drivers of variation in urban systems, but the details of these factors seem to differ. Additionally, prairie species may broadly be good candidates for future urban restoration efforts. My work contributes to the growing field of interpreting variation in urban restoration outcomes and may help guide future efforts to parse the responses of plant communities undergoing ecological restoration in urban systems going forward.
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