First Advisor

Richard B. Forbes

Term of Graduation

Summer 2001

Date of Publication

7-12-2001

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Biology

Department

Biology

Language

English

Subjects

Wetland ecology -- Oregon -- Beaverton, Reed canary grass -- Oregon -- Beaverton

DOI

10.15760/etd.4157

Physical Description

1 online resource (34 pages)

Abstract

Small urban wetlands are being destroyed and degraded at an alarming rate. One result of degradation is invasion by pest species, such as reed canarygrass (Phalaris arundinacea L. ). Reed canarygrass forms virtual monocultures in a wide range of wetland types. Wetlands normally have high plant species richness and abundance, which is widely believed to lead to faunal diversity. The purpose of the present study was to determine to what extent birds and mammals use a wetland dominated by reed canarygrass. The research was conducted at Tualatin Hills Nature Park in Beaverton, Washington County, Oregon. I examined three sites where reed canarygrass formed 75-100% of the plant cover. Mammals were inventoried using live traps, Museum Special rodent traps and pitfalls from August-October, 2000. Bird surveys consisted of one morning and one evening observation in each of four seasons. Each plot was walked on three different occasions in the spring to search for nests. Attention was also paid to other indications of animal use such as tracks and scat.

Only two species of birds and six species of mammals were observed utilizing wetlands invaded by reed canarygrass. Four of the six species of mammals were found where invasion by reed canarygrass was least and therefore, where plant heterogeneity was greatest. The two species of birds were not using the grass for nesting habitat.

Causes of these low numbers of birds and mammals utilizing reed canarygrass infested wetlands are probably multifactorial. By forming dense monocultures, reed canarygrass greatly reduces the diversity of food sources and nest sites. Furthermore, the density of the grass and the mat it forms upon dying probably make movement and nesting difficult for many vertebrates. The leaves are known to contain alkaloids that probably make the plant unpalatable to many herbivores. The seeds are small, readily shatter and fall to the soil beneath the mat, making their use by granivores difficult. By tolerating wide ranges of moisture, reed canarygrass simplifies the vegetation of entire wetland complexes. This study suggests that the resulting decrease in floral diversity is accompanied by a decrease in diversity of birds and mammals.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/44708

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