Graduate Thesis Or Dissertation

Vegetation-soil relations as a basis for resource management on the Ochoco National Forest of central Oregon

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  • The study was conducted on the Ochoco National Forest in central Oregon. Vegetation-soil relationships were evaluated for the following objectives: 1. Develop a sound ecological foundation on which total land management decisions may be based. 2. Evaluate forest succession, stocking, and growth to improve management. 3. Develop accurate range condition and trend guides. The concept of non-random distribution of plant communities in a continuum gradient was used to guide the investigation. This philosophy requires sampling the entire spectrum of vegetation and environmental variability in order to determine plant community groupings for classification purposes. Data were collected on a fifth-acre plot for trees, and on two 100-foot three-quarter-inch loop transects for subordinate vegetation. Forage production was determined on ten 9.6-square foot plots. Soil profiles were described according to standard procedure. Only vegetation free from grazing or logging disturbance was sampled. Vegetation was classified by use of association tables. Mathematical computations included standard errors and correlation analysis. Non-forest associations were: Artemisia rigida/Poa secunda on about six inches of soil, Artemisia arbuscula/Festuca idahoensis on about 14 inches of clayey soil derived from acid igneous rock, and Artemisia arbuscula/Agropyron spicatum on about 14 inches of clayey soil derived from basic igneous rock. These associations occur as natural openings in the forest zone due to soil properties inimical to tree establishment. Climax pine associations occurred on 12 to 30 inches of sandy, stony soil. Pinus ponderosa/Purshia tridentata/Agropyron spicatum occurs at lower elevations. Pinus ponderosa/Purshia tridentata/Sitanion hystrix occurs on acid igneous derived soils. Pinus ponderosa/Carex geyeri occurs on basic igneous derived soils. All are grazed by livestock and require open tree stocking for optimum tree growth. The Abies grandis/Calamagrostis rubescens association occupies more land area than all other forest types combined. It has been maintained in open Pinus ponderosa by natural, recurrent ground fires. With fire control, this association gradually moves toward a climax of fir. The Abies grandis/Bromus vulgaris association occurs at upper elevations. Dense forest cover makes it unsuitable for grazing. Management is different than for the Abies/Calamagrostis. Even though the Pinus contorta/Vaccnium scoparurn/Calamagrostis rubescens is successional, it was classified as an associes for management purposes. It pioneers on Abies/Bromus sites following conflagration fires. Four other vegetation associations were briefly described. Numerical variability within associations poses problems for development of range and forest management guides. In most cases, correlation analysis permits refinement of data. Variability is caused by the continuum effect of vegetation and environment. The information derived from this study is discussed for application in management. Mapping recommendations include a basic vegetation map with overlays for timber and range management use. Guides are presented for development of range condition and trend standards, interpretation of trend, and evaluation of management. Forestry guides include suggestions for silviculture, stocking and growth, and timber management. In addition, application in watershed and multiple use is briefly discussed.
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