Portland State University. Department of Environmental Sciences and Resources
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources
Environmental Sciences and Resources
Rubus -- Pacific Northwest, Blackberries -- Western Oregon, Plant invasions -- Pacific Northwest, Plant-water relationships -- Pacific Northwest, Plant ecology -- Pacific Northwest
1 online resource (2, xiii, 150 pages)
The factors influencing the invasive success of Rubus armeniacus (Himalayan blackberry) in the Pacific Northwest of North America are only partly understood, but have important implications for its management and for our understanding of the processes driving invasive plant proliferation in regions with seasonally fluctuating resources. I identified patterns of R. armeniacus occurrence and growth under widely ranging soil and light conditions in western Oregon. I found that light availability was a primary determinant of R. armeniacus occurrence and growth. I also found that R. armeniacus was tolerant of a wide range of soil conditions, notably coarse texture, and could form thickets on poor soils with only small reductions in growth. I proposed that an enhanced ability to tolerate dry conditions may contribute to the invasive success of R. armeniacus in the Pacific Northwest, especially in anthropogenically disturbed ecosystems. I attempted to verify this possibility by comparing water relations of R. armeniacus and two congeneric native shrub species during periods of wet and dry field conditions. My results demonstrated that, compared to the native species assessed, R. armeniacus is capable of more rapid water use when water is available, and more extensive water acquisition when it is scarce. In a third study I investigated associations among morphology, water relations, and growth rate among R. armeniacus and four confamilial shrub species native to the Pacific Northwest. I grew plants in the greenhouse, and found that R. armeniacus had more massive root and shoot systems, stored more water in its canes, and grew faster than several of the native species. I concluded that morphological advantages in water access and storage may help R. armeniacus maintain more rapid gas exchange though wet and dry periods than the native species, and thereby grow at a more rapid rate, especially in sites where other resources (notably light) are available. This research demonstrated that resource relations contribute to the uncommonly adept invasive ability of R. armeniacus in Pacific Northwest ecosystems, and identified a case where a plant invader in a seasonally fluctuating resource regime outperformed competing natives across the range of resource availability.
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Caplan, Joshua Sundance, "The Role of Water and Other Resources in the Invasion of Rubus Armeniacus in Pacific Northwest Ecosystems" (2009). Dissertations and Theses. Paper 5946.