Impacts of Restoration and Management on Plant Communities and Belowground Processes in the Chicago RegionPublic Deposited
Ecological restoration is a land management tool for biological conservation in areas where ecosystems are subject to a suite of natural and anthropogenic disturbances. This approach is particularly critical in urban areas where disturbances are often frequent and substantial. Restoration projects aim to re-establish an entire ecosystem, including the native organisms as well as the ecological processes and biotic interactions of those ecosystems for long-term sustainability. In practice, ecological restoration has primarily focused on establishing a diverse plant community while largely ignoring the belowground components of ecosystems. Surprisingly little is known about the complex relationships between soil factors, plant communities, and ecosystem processes in pristine systems, and even less is known about these relationships in restored or urban systems. In my dissertation, I ask: how do aboveground-focused management practices influence plant communities and belowground processes in the Chicago region? I address this question using research that spans spatial and temporal scales and includes different terrestrial habitats. I examine ecological patterns of restoration activities at sites replicated across a large landscape, plant-soil interactions at the site level, and interactions between plant tissues and fungal communities using molecular techniques. I also address these questions across temporal scales. Using a restoration chronosequence, I use a space for time substitution to investigate ecological patterns over large periods of time. In a manipulative field study, I examine plant-soil dynamics over a period of 4 years. My study sites include private and publicly owned lands that represent a range of upland terrestrial habitats in the Midwestern U.S. and are managed by citizen scientists, government agencies, and professional contractors and combinations therein. My highly replicated, regionally comprehensive, and ecologically and politically representative experimental approach ensures that conclusions from my research have direct and immediate impacts on the understanding these ecosystems and how they are managed. In Chapter 1, I describe the development of a collaborative network of protected sites that capitalize on the shared best management practices in the Chicago region. This network links on-the-ground restoration and land management activities with ecological research. This chapter provides the conceptual and experimental framework as well as experimental methods for collecting baseline data used in the subsequent studies. In Chapter 2, I describe how patterns in plant community structure and soil nutrient levels in woodlands and prairies differ with management duration and relate to each other. I found that in prairies, land use history is the most important factor in determining plant community assemblage followed by more recent land management activities. In woodlands, the initial action of removing woody invasive taxa is critical to initiating ecosystem restoration, while on-going management maintains community composition. In Chapter 3, I used geo-spatial analysis to develop a model of woodland degradation that integrates invasive shrub density, exotic earthworm biomass, and soil nitrogen (N) availability. Using this model, I found that unrestored sites have significantly higher invasive shrub cover, exotic earthworm biomass, and soil nitrogen availability than managed sites, regardless of their time under management. I also identified notable exceptions to these patterns that may be used to direct and prioritize future investigations and ultimately, lead to more cost-effective restoration efforts. In Chapter 4, I examine the decomposition rates of leaf litter in remnant and former row-crop agricultural prairie ecosystems across the restoration chronosequence and describe the functional and community composition of the decomposer fungal communities. I found that leaf chemistry was a more important driver of litter mass loss than either land use history or management duration. I also found that although fungal communities differed in composition, they remained functionally similar across all sites. In Chapter 5, I conducted a manipulative field experiment exploring traditional and novel methods of restoration following the invasion of a non-native shrub (Rhamnus cathartica). I determined that amending soils with woody mulch following buckthorn removal significantly reduced reinvasion over the four-year field study period but that these results are not due to a reduction in soil N availability. Manipulative studies in the greenhouse similarly showed that mulch-amended soils significantly reduced buckthorn germination, seedling growth, and transplanted sapling growth. The results of this study suggest that incorporation of ground woody material into the soil following aboveground removal may facilitate restoration following European buckthorn invasion In this dissertation, I set out to examine and document how aboveground-focused management practices influence plant communities and belowground processes in the Chicago region. My research shows that land management practices influence plant community composition and soil nutrient availability across a range of ecosystem types. From a landscape perspective, these results are important in that they demonstrate that local correlations between above and belowground communities differ from those on the broader scale. From an applied perspective, my research informs land management practice and restoration of temperate woodlands and globally threatened tallgrass ecosystems, but also contributes to our knowledge on the processes and interactions between plant and soil communities that determine biological diversity in the Midwest US, especially in urban ecosystems.