Date of Award:

5-2003

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Ecology

Committee Chair(s)

James W. Haefner

Committee

James W. Haefner

Committee

Richard S. Inouye

Committee

James A. MacMahon

Abstract

The importance and mechanisms of species interactions are undetermined in most successional systems. I used correlations and null modeling to detect pairwise species associations between 33 plant species in the first nine years of secondary succession after logging and burning in a western Oregon Cascade forest. I tested for correlations between each species and soil nutrients, nonvegetative ground cover, and surrounding vegetation. More positive than negative associations were found at all sampling times. The proportion of positive associations decreased and negative associations increased through time. Up to 42% of associations at a sampling time were explicable by shared positive correlations with surrounding vegetation. One domjnant shrub species, Berberis nervosa, may be primarily responsible for the decline of four early seral species. The associations indicated diffuse facilitation is of primary importance in the stressful early successional environment, and microsite availability and interspecific competition become more important later.

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