Graduate Thesis Or Dissertation
 

Exploring Alternative Approaches for Native Plant Production and Ecological Restoration in the Pacific Northwest

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h415pj11v

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  • Global recognition of the need for ecosystem restoration and revegetation following natural and anthropogenic disturbances has been growing in recent years. Successful programs often depend on the use of nursery-grown seedlings and appropriate mitigation of limiting factors on outplanting sites. Nursery production of high-quality native plants for restoration can be a vital component in effectively remediating degraded ecosystems, protecting native fauna and flora, soil, water and air, and sustaining economies. Holistic seedling production should consider the environmental impacts of elements such as nursery seedling growing media components; improvements could be made to better derive such materials from sustainable sources and mitigate the alteration of habitats or depletion of natural resources. Further, the implementation of weed mitigation approaches should make use of materials that do not increase cost of crop or timber production, and most importantly do not affect soil health or water quality. To date, organic wastes like anaerobic digestate (AD) are understudied for the production of forest plants such as western redcedar (Thuja plicata Donn ex D. Don) and black cottonwood (Populus trichocarpa Torr. & A. Gray), and there are unresolved questions about the effectiveness of some weed control treatments. Therefore, the objectives of this research were to explore alternative approaches for native plant production and ecological restoration in the Pacific Northwest. Chapter 2 describes a study on the assessment of AD as a principle component of forest tree seedling growing media. Results showed that AD was more nutrient-rich than Sphagnum spp. (peat moss, Pe), particularly in nitrogen (N), phosphorous (P) and potassium (K). It also showed that seedlings cultivated in AD-amended media attained equal or superior growth compared to those cultivated in Pe-based media, while using less water. The results suggested that AD holds high promise as a substitute for Pe in nursery growing media for the production of these native tree species. Chapter 3 describes a study evaluating the efficacy of four weed control treatments in reducing reemergence of Himalayan blackberry (Rubus armeniacus Focke) and their effects on soil properties and growth and physiology of planted western redcedar in a degraded riparian ecosystem in Carnation, Washington. Results show that carbon (C) and nitrogen (N) concentrations were significantly lower in soil treated with a manual weed removal plus a 5” layer of large woodchips and a geo-jute net (t2) compared to those treated with other mitigation approaches or the control (no treatment), but only in well-drained soils. With the exception of fall 2020, t2 also resulted in significantly higher soil temperatures. A mitigation treatment of a 5-cm layer of corrugated cardboard plus a 5” layer of large woodchips and geo-jute net after manual weed removal (t4) and t2 were most effective at reducing weed reemergence in the initial months following treatment, but this effect diminished completely over time. Although there was no treatment effect on height or root collar diameter growth of western redcedar seedlings, those planted in t4 photosynthesized at a greater rate than those planted in control plots. From these studies, I conclude (1) AD is a promising alternative to Pe and should be further studied for use in the production of other species; and (2) mulching did not provide a gain in seedling performance or weed control over the scope of this research trial.
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