Advisor

Mitchell B. Cruzan

Date of Award

1-1-2011

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Biology

Department

Biology

Physical Description

1 online resource (v, 46 p.) : ill. (some col.), 1 col. map

Subjects

Habitat invasibility, Invasion resistance, Propagule pressure, Brachypodium -- Ecology -- Pacific Northwest, Invasive plants -- Ecology -- Pacific Northwest, Forest ecology -- Pacific Northwest

DOI

10.15760/etd.41

Abstract

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.

Description

Portland State University. Dept. of Biology

Persistent Identifier

http://archives.pdx.edu/ds/psu/7021

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