Graduate Thesis Or Dissertation
 

The quantity and composition of ground vegetation in different light environments under a Douglas-fir, Pseudotsuga menziesii (Mirb) Franco, stand in the Oregon Coast Range

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v692t820r

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  • The relationship between ground vegetation and light intensity under a 60 to 65-year-old Douglas-fir forest was investigated. Biomass and height of ground vegetation were measured and cover was estimated on small sample units (30 centimeters in diameter) on permanent research plots, one-acre in size, on the George T. Gerlinger Experimental Forest at Black Rock, Oregon. Three thinning intensities, from light to heavy, have been maintained on the research plots over approximately 20 years. Light intensity was measured with photosensitive paper as a light integrator for one day in the summer. Also basal area of the trees and taller shrubs surrounding the sample units of ground vegetation were measured. These variables were assumed to represent root competition between ground and overstory vegetation. The results show that with increased thinning intensity the average light intensity near the ground, the average cover and height of ground vegetation all increased. But no significant differences were found in the biomass of ground vegetation between different thinning intensities, because of the great variation in biomass within each research plot. However, no meaningful correlation was found between either biomass, cover, or height of ground vegetation and light intensity on the small sample units. A multiple linear regression analysis with the additional variables of the basal areas of the surrounding trees and shrubs also revealed no meaningful correlation. The most important species on the research plots were Oregon grape (Berberis nervosa), bracken fern (Pteridium aquilinum), and a few herbaceous species such as Trientalis latifolia. There was too much inexplicable variation in the data also when examining the response of the most important species to light separately, although the variation was smaller. The regime of light intensity measured (1 to 30 percent of full sunlight) seemed to be sufficient for growth of these shade tolerant species of ground vegetation. The results show clearly that, under the conditions of the Douglas-fir stand studied, the light intensity as measured on the sample units does not relate to the amount and composition of ground vegetation on these sites. Other unknown factors seem to have more influence on the distribution and quantity of ground vegetation in this Douglas-fir stand.
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