Sitka black-tailed deer (Odocoileus hemionus sitkensis Sm.) prefer understory forages growing beneath a forest canopy despite a greater abundance of the same plant species in forest clearings. This research examined responses of the deciduous shrub - blueberry (Vaccinium ovalifolium), to test the hypotheses that 1) forage is less nutritious and less palatable when grown in clearings than in forest understories, and that 2) changes in the plant carbon/nitrogen (C/N) ratio in response to light and nitrogen supply determine forage nutritional quality. Responses to irradiance and nitrogen supply were examined with respect to plant physiology, morphology, biochemistry and nutritional quality in three phases : 1) under controlled conditions in a growth room, 2) with manipulations in a field experiment and 3) along natural gradients of light and nitrogen in the native forests. The results were highly consistent from the growth room to the field. Light strongly affected plant physiological responses, including photosynthesis, relative growth rates and growth efficiency, whereas nitrogen had little effect. In regression analyses, leaf morphological properties, including specific leaf weight and leaf succulence, were the best predictors of relative growth rates (R2=.67). Irrespective of nitrogen supply, the biochemical properties of sun leaves included higher concentrations of starch, nonstructural carbohydrates and % lignin + cutin in the cell wall, but lower concentrations of structural polymers, total nitrogen, free amino acids, and ratio of free amino acids : total N, compared to shade leaves. Sun leaves also were slightly higher in digestible energy, much lower in digestible nitrogen and presumably less palatable due to higher tannin concentrations, compared to shade leaves. Tannins were directly correlated to specific leaf weight (R2=.89). Regression equations based upon specific leaf weight, leaf succulence and leaf structural polymers accurately predicted field values for digestible nitrogen (R2=.91) and digestible energy (R2=.96) in foliage. Nutritional properties of blueberry forage grown under variable irradiance in the natural stands matched predictions based upon results from the growth room and field. Compared to even-aged stands and oldgrowth, leaves of plants grown in clear-cuts were similar in digestible energy, much lower in digestible nitrogen, and presumably less palatable due to higher tannin concentrations. / Graduation date: 1990

Habitat use by mule deer, particularly in relation to use by cattle and by California bighorn sheep on the bighorn winter-spring ranges of Flatiron Mountain was studied from January 1968 through November 1969. Observations were made of (1) food habits, (2) forage production and utilization, (3) the effect of spring and summer utilization on subsequent forage production and (4) spatial and temporal distribution of range use. The results indicate that competition for forage between the native ungulates, deer and sheep, is largely obviated by differential habitat use. This may point to long term evolutionary ecological niche specialization. Some competition for forage occurs for a short period in the early spring when both ungulate species seek succulent new grass, the supply of which is at first limited. Cattle use of the winter-spring ranges was excessive and the diets of cattle and the native ungulates are similar, with the exception that utilization of grass by deer was less. Range use by cattle contributed to intra-specific cattle-deer competition on the grasslands in the spring and cattle-bighorn competition on the grasslands during the winter. The study of spring range utilization indicated that deer use was not detrimental to the 1969 annual forage production in areas used by deer. Spring range utilization by bighorn or bighorn in combination with deer reduced the standing crop of forage produced on the Agropyron spicatum dominated winter-spring ranges. Sheep utilization on South Slope during the summer, when forage growth was declining, further reduced the amount of forage available to the wintering bighorn population. / Land and Food Systems, Faculty of / Graduate