Mature forests, litterfall and patterns of forage quality as factors in the nutrition of black-tailed deer on Northern Vancouver Island
Creators: name: Rochelle, James Arthur
Publisher: name: University of British Columbia
Year: 2010

description: The relative availability and quantities of black-tailed deer (Odocoileus hemionus columbianus [Richardson]) forage supplied by litterfall and understory vegetation during winter were assessed in selected mature conifer stands in the Nimpkish Valley of northern Vancouver Island. Composition and rates of litterfall and its use by deer were determined as were year-long food habits of deer utilizing mature conifer stands and logged areas. Monthly patterns of variation were determined over a 1-year period for a number of measures of forage quality including in vitro dry matter digestibility (DDM), crude protein, cell contents, cellulose, hemicellulose and lignin. Analyses were made on ten forage species, known to be major dietary items of deer in the study area. Nutrient characteristics were compared between plants growing beneath a mature forest canopy and in cutover areas. Rates of DDM for selected species and DDM of a series of forage mixtures were determined. Relationships of the various nutrient parameters to each other were examined. Energy contents as indicated by volatile fatty acids (VFA) in products of in vitro fermentation were determined for the ten species examined. Patterns of monthly and seasonal variation in concentration, composition and caloric content were defined and contrasts were made between forested and cutover areas of collection. Characteristics of deer rumen contents including dry matter, crude protein and caloric content were determined monthly over a 1-year period, and related to deer food habits and nutrient characteristics of forage species. Deer condition throughout the year and in relation to forage quality was assessed through determination of weight and amounts of fat deposited in selected tissues. Levels of blood urea nitrogen (BUN) were determined relative to levels of protein and energy intake and weight loss patterns. Amounts of litterfall suitable as forage equal or exceed year-around quantities of available rooted vegetation in some mature conifer stands. Lichens made up 86 percent of forage litterfall. Monthly litterfall rates varied in response to weather conditions. Deer consumed fallen lichen Alectoria and Bryoria spp. Litterfall provides a relatively small but continuous source of forage during the winter. Forbs and shrubs were of major and equal importance in the annual diet of deer. Epilobium angustifolium was the most heavily used species during the spring to fall period; use of conifers and lichens was greatest in winter. Reduced forage availability in winter was reflected in fewer species present in rumen samples. Forage characteristics varied distinctly in response to phehological changes in the plant. Lichens were the most digestible forage but contained less than 2 percent crude protein. Conifers contained less than the 7 percent protein required for maintenance during most of the year. Consistently higher nutrient levels in plants from forested or cutover areas were not observed during any season of the year. Digestibility of forage mixtures was higher than expected from component digestibilities; Alectoria sarmentosa had an enhancement effect on other components of mixed diets. Most species were fully digested within 24 hours. Rumen fill, dry matter and crude protein contents reflected forage quality changes and deer food habits. Energy levels of forage plants varied seasonally in response to phenological change; Epilobium angustifolium displayed the highest energy content of the species examined. Lichens and ferns were lowest in energy content. Peak energy content in most plants occurred in summer. Ruminal VFA concentrations followed the seasonal patterns observed in forage plants; peak concentrations occurred in spring and summer and were significantly higher than in winter. Maximum weights of deer occurred in fall-early winter and minimums occurred in late winter. Greater weight gains occurred in the late summer-early fall period when energy demands above maintenance were probably lowest. Mesentery weight and kidney fat index appeared to be suitable condition indicators. Blood urea nitrogen was a good indicator of recent protein intake. BUN levels did not increase during periods of weight loss, suggesting tissue catabolism did not occur.