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Deer food production in certain seral stages of the coast forest Gates, Bryan Rodd

Abstract

This study was designed to determine which seral stages of the regenerating coast forest are most efficient at converting radiant energy into energy available as seasonal deer foods, and if the most efficient stages are most intensively used by deer. Populations of Columbian black-tailed deer (Odocoileus hemionus columbianus Richardson) in coastal British Columbia have been reported to reach maximum levels soon after logging and slash-burning, and to decline as. succession advances. The efficiency of a deer range in producing food has been suggested as a factor influencing reproductive success and thus, population density. Seasonal forage preferences were determined, through rumen content analysis. Cover composition up to four feet in height, and summer and winter estimates of quantity, variety and nutrient quality of the important food species were obtained in different seral stages. These data were then related to the intensity to which deer utilized each seral stage, as indicated by the abundance of pellet groups. An early salal-catsear (Gaultheria-Hypochaeris) association develops three to five years after slash-burning. This type was preferred by deer during spring and early summer. Herbaceous plants formed 60 per cent of the spring-summer diet and were represented by more species, covered more surface area, and produced more available forage in this seral stage than in any other. A salal-Douglas fir (Gaultheria-Pseudotsuga) association develops 12 to 15 years after slash-burning. This type was preferred during autumn and winter. Shrub and coniferous species formed 70 to 80 per cent of the autumn-winter diet and were represented by more species, covered more surface area, and produced more available forage in this seral stage than in any other. In addition, the crude protein, mineral, and ash contents of the important evergreen foods were higher when eaten (autumn-winter) than at other times. Heaviest deer use occurred in the seral stages where these evergreens were most available. The nutrient content of key foods changed significantly with season, and there was evidence of selection by deer of the most nutritious plants available. Tests to demonstrate declines in nutrient levels as seral succession advanced between the fourth and fourteenth years were inconclusive, particularly since there is a likelihood of significant declines occurring in the initial four years. However, seasonal and successional changes in food quality are believed to be a factor influencing range selection. It is concluded that the numbers of deer within a logged unit of coast forest are affected by the efficiency at which food is produced. Numbers within the whole community are affected by the availability of ideal food-producing units for each season. A further hypothesis is suggested which states that sustained populations cannot be expected in a logged coast forest because seral succession will inevitably cause regression of range quality.

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