First Advisor

Robert Tinnin

Term of Graduation

Spring 1997

Date of Publication


Document Type


Degree Name

Master of Science (M.S.) in Biology






Forest plants -- Oregon -- Beaverton, Plant communities -- Oregon -- Beaverton, Plant succession -- Oregon -- Beaverton, Tualatin Hills Nature Park (Beaverton, Or.)



Physical Description

1 online resource (2, 40 pages)


Tualatin Hills Nature Park is an urban woodland located in Beaverton, Oregon. The park is owned and managed by Tualatin Hills Park & Recreation District. Vegetation in the park is in a state of secondary succession following a long history of disturbance. The site provided an excellent opportunity to study the recovery of a natural woodland in an urban setting in the northern Willamette Valley.

The purpose of this study was to analyze the species composition, structure, and successional trends of the woodland vegetation in Tualatin Hills Nature Park. A secondary purpose was to determine if there were any natural grouping among the sampled plant assemblages.

Stratified random sampling was employed to collect data in eight relatively homogeneous, yet distinct plant assemblages. There were four mixed coniferous, three mixed hardwood, and one shrubland plant assemblages. 100 m2 circular plots, each containing a 10 m line transect, were used to collect basal area and density data of trees and frequency and cover data of trees and shrubs from mid-July to mid-October, 1995.

Cluster analysis of basal area and cover data was used to determine if there were any natural grouping among the sampled plant assemblages. Both applications of cluster analysis grouped the mixed coniferous and mixed hardwood assemblages separately. The results of this study showed that the two types of plant assemblages were characterized by both a distinct set of tree and shrub species as well as the trees that were reproducing in the stands. This study found that the woodland vegetation in Tualatin Hills Nature Park is typical of the Willamette Valley and supports the hypothesis that under the current condition of fire suppression Ables grandis is the climax species of the Willamette Valley.


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