Graduate Thesis Or Dissertation


Influence of range improvement practices on composition, production, and utilization of Artemisia deer winter range in central Oregon Public Deposited

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  • Recent emphasis on range improvement of sagebrush-bunch-grass types in Oregon has underscored the need for better understanding of their importance to deer winter range management. The objectives of this study were to evaluate the impact of various sagebrush control practices on the composition, production, and utilization of deer forage plants during the critical winter period. Field studies continued from June, 1963, to August, 1965, at various locations throughout the Fort Rock and Silver Lake deer winter range units in northern Lake County. Range improvement effort has been directed primarily toward poor condition communities dominated by big sagebrush (Artemisia tridentata). Consequently, sampling was practically restricted to these communities although other types were recognized to be of equal or greater value to deer. Two basic approaches were followed. The first consisted of establishing three experimental treatment blocks in stands representative of extensive big sagebrush communities. Quantitative plant ecological data were taken prior to treatment as a basis for interpreting later successional changes. Four commonly-accepted range improvement methods--spraying, spray-seeding, rotobeating, and plow-seeding--were initiated on two-acre strips in each block with an additional untreated strip forming a control. Half of each block was fenced to determine differences resulting from livestock exclusion. Periodic resurveys over five to seven years are scheduled. The second approach entailed a paired-macroplot study of selected existing projects where spraying, rotobeating, burning, and seeding treatments had been used. Similarity of soils and other physical site factors formed the basis for pairing plots and inferring similarity of pretreatment vegetation. Floristic differences among paired plots were quantified by data on shrub coverage, density, and height; basal area of herbaceous species; and frequency of all species. All treatments reduced shrub cover sharply but rotobeating resulted in the greatest shrub survival. Herbaceous species response was variable but only seeded stands of crested wheatgrass showed marked increases in basal area of desirable forages. Production data indicated wide fluctuations in shrub herbage available for winter use. Estimated big sagebrush herbage production on untreated stands in oven-dry pounds per acre ranged from 23 to 449 and averaged 234. Winter-active grass herbage was most abundant on crested wheatgrass seedings, particularly those grazed heavily by livestock in the preceding growing season. Estimated production ranged from 37 to 126 and averaged 75 pounds per acre of oven-dry material. Green growth of native grasses was important feed for deer primarily during the latter part of the winter period. Bitterbrush, the key browse plant for deer on the study area, sustained excessive levels of use at all locations studied. Recent changes in livestock grazing season have effectively minimized use of bitterbrush by this class of grazing animal. Bitterbrush mortality has been high and both vigor and stand regeneration are generally poor. It was concluded that effects of existing improvement programs were usually minor compared with the declining condition of the all-important bitterbrush stands resulting from excessive winter populations of deer. Species other than bitterbrush were utilized moderately to lightly. Green rabbitbrush showed a consistently higher percent of plants grazed and mean percent utilization than big sagebrush on untreated stands. Seedings and other range improvements tended to create a diversified plant cover and forage resource that appeared to enhance use of the untreated sagebrush. Green grass material was significantly higher in crude protein percentage than current annual growth of shrubs. Management emphasis should be directed toward positive programs of vegetational manipulation designed to increase forage values of big sagebrush types for deer as well as livestock.
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