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Browsing by Subject "ecological restoration"

Now showing 1 - 3 of 3
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    Effects of Flooding and Light on the Performance of Potential Replacement Species in Black Ash Wetland Forests
    (2022-04) Keller, Gwendolen
    Within black ash wetlands in the western Great Lakes region, black ash (Fraxinus nigra Marshall) is a foundational species that controls hydrologic regime, nutrient cycling, and wildlife habitat. The role of black ash in these stands makes them particularly vulnerable to the invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae). One strategy that has been suggested to mitigate the impact of this invasive insect is the increase of tree species diversity through artificial regeneration, however, there is limited information available on how potential replacement tree species respond to shade and flooding. We used controlled greenhouse and field experiments that manipulated flooding duration and intensity as well as shade to explore early survival, growth, and physiology of 23 different tree species that vary in shade and flood tolerance. Measurements of seedling physiology, growth, and survival were taken throughout the growing seasons of 2020 and 2021. Results indicate that bald cypress was able to tolerate the most extreme flooding conditions simulated in the study: water table at the soil surface for 15 weeks. American elm, sycamore, and river birch were tolerant of water tables between 0 and 14 cm below the soils surface for up to 15 weeks. Northern white cedar, red maple, tamarack, swamp white oak, and yellow birch had high survival and growth rates with the water table at the soil surface for up to 6 weeks. Finally, black walnut, sugar maple, white spruce, white oak, red pine, and bitternut hickory responded poorly to flooding of any duration. Results indicate that water table depth has a greater influence on seedling growth and gas exchange rates than light reduction, especially at light levels likely to be found in black ash wetlands. Since shade treatments were generally not a significant impediment to early growth, survival, and gas exchange rates, natural resource managers should focus on matching the flood tolerance of potential replacement species to local site hydrology.
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    Harvesting native seed to supply landscape-scale restoration: evaluating risks and sustainable practices
    (2016-06) Meissen, Justin
    Seed supply limits large-scale restorations, which often rely on seed collection from remnant ecosystems. Overharvesting seed may deplete populations, exacerbate seed limitation, and jeopardize ecosystem integrity, but these risks have not been formally studied. Many life history traits are linked to species’ reliance on seed reproduction, and so may provide a useful framework to address seed harvest risks. I evaluated whether life history traits predict susceptibility to overharvest by comparing tallgrass prairies in Minnesota (USA) harvested at varying frequencies (every year, once per 3-5 years, unharvested). I identified species less likely to occur on frequently harvested sites then tested whether lifespan, clonality and seed production predicted harvest sensitivity. Short-lived, non-clonal species were sensitive to seed harvest while long-lived clonal species were not, suggesting that life history traits provide a means to predict seed harvest risk. To verify the predictive utility of life history traits and determine extinction risks from seed harvest over long restoration timeframes (25 years), I used matrix models of clonal Solidago canadensis and Anemone canadensis and non-clonal Rudbeckia hirta, Packera aureus, Zizia aurea, and Liatris ligulistylis to simulate seed harvest and extinction risk. I simulated 5 scenarios: no harvest; annual harvest at 50%/75% intensity; and triennial harvest at 50%/75% intensity. Non-clonal species were insensitive to triennial and 50% harvest, but susceptible to extinction risks of up to 92% with annual 75% harvest. Clonal species were insensitive to all harvest scenarios. To maintain populations of non-clonal species in the long-term, high intensity annual harvest should be avoided. To demonstrate the risk of overharvest in short-lived, non-clonal species and determine sustainable harvest regimes, I conducted a field experiment varying seed harvest intensity (0, 50%, or 100% seed removed) and management (burned or unburned) for R. hirta populations. I compared seedling recruitment and seed production among treatments, and found that seed production nearly doubled with burning. Moderate intensity harvest with burning allowed high levels of seedling recruitment, but high harvest intensity prevented recruitment, as predicted for a short-lived, non-clonal species. A regime combining moderate intensity harvest with fire management provides seeds while also conserving at-risk seed donor sources.
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    Seed sourcing for ecological restoration in an era of climate change: Impacts of source latitude and hybridization
    (2022-11) Rushing, Naomi
    In Minnesota, tallgrass prairie ecosystems currently occupy less than 1% of their former range. The importance of maintaining and restoring this dwindling ecosystem is well recognized but the ecological restoration process is complex, particularly in the current era of climate change. Successful establishment and persistence of restoration populations depends in large part on seed source selection. Previous research and discussion have explored the importance of maintaining local adaptation and genetic diversity. There has also been discussion of intentionally translocating populations in specific directions in response to ongoing climate change. In an effort to inform seed sourcing guidelines, the research presented here investigates (1) the implications for restoration of translocating populations across latitudes, (2) the phenological and fitness outcomes of hybridization between distinct populations, and (3) genetic effects contributing to differences between divergent populations. Chapter 1 focuses on the phenological and fitness impacts of translocation along a latitudinal gradient within the state of Minnesota using a common garden style approach and three perennial prairie species. Chapters 2 and 3 expand upon this work and investigates the impact of translocation on an annual prairie species sampled across a latitudinal span from Minnesota to Missouri, as well as investigating the outcome of hybridization between these divergent populations. Our results highlight the importance of latitude of origin to both phenology and fitness of translocated populations, as plants from more northern locations tended to have earlier timing of flowering and fruiting in the common gardens, as well as higher fitness for all of our study species. In addition, Chapters 2 and 3 demonstrate the potential positive impacts of hybridization across a range of geographic distances with no indication of outbreeding depression, as hybrid generations tended to have higher mean fitness in the common gardens than the parental generations. However, phenological mismatch between seed source and planting site in populations translocated across large latitudinal distances can result in low fitness and limit hybridization with local populations. Taken together, these results highlight the benefits of hybridization between populations, while demonstrating the potential drawbacks of translocating populations across large latitudinal distances.