The invasibility, or susceptibility of an ecosystem to biological invasion is influenced by changes in biotic and abiotic resistance often due to shifts in disturbance regime. The magnitude of invasive propagule pressure interacts with an ecosystem's invasibility to determine the extent of a biological invasion. I examined how propagule pressure, forest community structure and disturbance interact to influence the invasibility of temperate Pacific Northwest forests by the newly-invasive grass, Brachypodium sylvaticum. My goal was to identify which of these factors is most instrumental in enabling the shift from establishment to population growth in B. sylvaticum at the edge of its expanding range.
Both observational and experimental studies were employed to identify the many ecological components of this problem. Ecological sampling methods were used to identify trends in B. sylvaticum habitat preference and signs of habitat disturbance. In addition, an experimental study was performed to test the effects of soil and vegetation disturbance on B. sylvaticum seedling propagation. I found that while soil disturbance did not have a significant effect on seedling propagation, vegetation disturbance was implicated in B. sylvaticum spread. Higher propagule pressure and coniferous forest type were also strong predictors of increased B. sylvaticum seedling propagation and survival within established sites. My study demonstrates how propagule pressure and plant community dynamics interact to shift the invasibility of Pacific Northwest forests and facilitate the transition from establishment to spread in the invasion of B. sylvaticum.
|Advisor:||Cruzan, Mitchell B.|
|Commitee:||Eppley, Sarah, Sytsma, Mark|
|School:||Portland State University|
|School Location:||United States -- Oregon|
|Source:||MAI 50/01M, Masters Abstracts International|
|Subjects:||Ecology, Conservation, Environmental science|
|Keywords:||Disturbance, False brome, Habitat invasibility, Invasion resistance, Population growth, Propagule pressure|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be