Nutritional ecology of cervids in old-growth forests in Olympic National Park, Washington

Graduation date: 1983Nutritional ecology of unhunted and sympatric populations of\ud Roosevelt elk, Cervus elaphus roosevelti, and Columbian black-tailed\ud deer, Odocoileus hemionus columbianus, was investigated in old-growth\ud forests of the Hoh Valley in Olympic National Park, Washington, from\ud September 1979 to November 1981. Seasonal diets of both cervids\ud generally were comprised of common forages; relative availabilities of\ud other preferred forages minimized their contributions to the diet of\ud either ungulate. Hemlock, swordfern, oxalis, and alder were the most\ud common dietary components on an average annual basis. Levels of crude\ud protein, dry matter digestibility and phosphorus in important forages\ud varied with phenology, but seasonal trends were more pronounced for\ud shrubs and grasses than forbs and trees. Dietary levels of those\ud nutritional attributes for both elk and deer varied seasonally in the\ud following ascending order: winter, fall, summer, spring. Protein and\ud phosphorus appeared to be adequate in diets, but low in vitro\ud digestibilities suggested that digestible energy may be limited.\ud Levels of sodium and selenium were low in most forages and suggested that dietary levels also were low. No significant differences in\ud seasonal diet quality were demonstrated between deer and elk. Fecal\ud nitrogen of both cervids was correlated with dietary protein and\ud provided an index to seasonal changes in nitrogen intake. Sympatry of\ud elk and deer was typified by 1) a high degree of dietary overlap, 2)\ud diets that seemed to afford little opportunity for partitioning plant\ud parts, 3) a similar pattern of food acquisition in major foresttypes,\ud and 4) heavy use of the forage base to the point of\ud restricting distributions of preferred forages and influencing the\ud physiognomy of the shrub layer in some forest communities. Those\ud observations suggested that one cervid should competitively exclude\ud the other. It was speculated that sympatry was enhanced by the\ud spatial heterogeneity of the old-growth forest, in that large numbers\ud of downed trees created areas only accessible to and used by deer.\ud Cervids probably were limited by undernutrition and low reproduction,\ud both consequences of maximum density and theoretically low forage\ud availability and quality