Graduate Thesis Or Dissertation


Early stages in plant succession on Douglas fir clearcuts on the Mary's Peak watershed near Corvallis, Oregon Public Deposited

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  • This study has been concerned with the patterns of vegetative changes which occur during the first five years following logging and burning on Douglas-fir clear cuts. Knowledge of the successional sequence in the coastal forests of western Oregon is of primary importance to those concerned with the management of this resource. From the more theoretical point of view, there are many unique features associated with this type of vegetation of special interest to the ecologist. Published accounts of studies in Oregon and Washington have been of a generalized nature. None have approached a localized area with the degree of intensity attempted in this study. Due to its close proximity to Oregon State University and the cutting and burning history of the area, the Mary's Peak Watershed has been especially suitable for this study. Mary's Peak is the highest point of the Oregon Coast range having an elevation of 4,097 feet. The Corvallis watershed is located on the eastern slope of the peak and includes both the Rock Creek and Griffith Creek drainages. The area is about five miles long east and west by four miles north and south. The area is managed as a unit by the United States Forest Service. Due to the marine influence, the area has a humid climate averaging approximately 65 inches of precipitation annually with an annual mean temperature of approximately 52°F. Soils are basaltic in origin and are primarily clay loam in texture. In 1950, an epidemic of Douglas fir bark beetles made necessary a program of development which included cutting of dead and infected trees and establishing a road system. Cutting was restricted to small clear cuts. The vegetation in the study area is a Douglas fir-vine maple association. Gaultheria shallon and Berberis nervosa dominate the forest floor with traces of Castanopsis, Corylus, and Cornus. Study plots were located on nine clear cut and burned areas ranging in elevation from 1,300 to 2,800 feet and including north, south, and east exposures. Nineteen study plots, which were 100 x 100 feet, were established in uniform vegetative areas. Plots were also established in the undisturbed areas adjacent to the clear cuts for comparative purposes. Vegetative sampling was done using a device called an ocular point frame which provided a reliable indication of vegetative cover. Sampling was done in both the spring and fall on the second, third, fourth, and fifth years following burning. The stable undisturbed vegetation was sampled only once. Results of the five-year study showed a general increase in total number of plant species. The average total vegetative cover rose abruptly the third, fourth, and fifth years. An analysis indicated that south exposed plots had the greatest vegetative cover the first five years after burning. East plots ranked second and north plots third. By the fourth year, average cover values on clear cut areas exceeded the cover values of understory vegetation on the adjacent uncut forest. Analysis of data regarding seasonal variation indicated sharp decreases in total cover from spring to fall during the first three years. Increasing amounts of perennial vegetation during the fourth and fifth years reduced this seasonal variation markedly. In terms of mean cover trends, the annual herb, Senecio sylvaticus, dominated the second year; Lotus stipularis and Circium vulgare, the third; Lotus and Holcus lanatus , the fourth and fifth. All plant species indicated a wide range of cover values on the plots sampled. Some consistent trends in the sequence of cover dominance are noted.
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