Table 2--Percentage composition of foliar fatty acids of red alder1/ 1/Numbers following fatty acids indicate number of carbon and number of double bonds, respectively. Percents are averages of three composite samples each. the lowest concentrations (0.2, 0.6 percent). During the growing season, levels of lauric, myristic, and linolenic increased, whereas those of stearic, oleic, and linoleic decreased; palmitic concentrations remained unchanged. Discussion and Conclusions Results show that in June when utilization by deer was minimal, red alder leaves contained adequate levels of minerals, available carbohydrates, protein, and fats to satisfy the nutritional needs of herbivores, including deer (Maynard 1951). leaves were also succulent, moderately acidic, had enough roughage as shown by the contents of fiber and lignin, and contained nontoxic levels of nitrates as well as fatty acids which are usually found in palatable plants. The total phenols in the leaves, however, were quite high; they amounted to over 10 percent of the dry matter and greatly exceeded levels found in plants browsed by black-tailed deer in winter (Radwan and Crouch 1974). Comparison of the June and September leaves indicated many variations in most chemical constituents. Thus, as leaves grew older and became more preferred by deer in September, moisture, acidity, protein, and phenols had decreased, while available carbohydrates and fats were increased. Fatty acids also changed in their composition during the same period of time. Obviously, it is impossible to state which change or combination of changes were actually responsible for the increased preference or the mechanism by which any of these factors were operating. One may speculate, however, that changes in fats and phenols were the important factors. That changes in these two leaf constituents were much greater than those shown by remaining constituents tends to support this speculation. Crude fat also is recognized as a high energy food source for animals, and associations of high fat contents in forages with high preference by some animals have been reported (Hardison et al. 1954, Louw et al. 1967). Phenols, on the other hand, have been generally considered as defense compounds which protect plants from their natural enemies, including herbivores (Levin 1971). Furthermore, tannins, which are estimated here as total phenols, have been shown to reduce palatability and digestibility of some plants in ruminants (Wilkins et al. 1953, Donnelly and Anthony 1973); and their great decline in September could very well account for the increased utilization of the leaves in the fall. Factors affecting animal preferences for plants are extremely varied and complex. Accordingly, we recognize that chemical constituents other than those reported here or nonchemical factors such as differences in availability of preferred food may have influenced deer preference. Literature Cited Arnold, G. W., and J. L. Hill. 1972. Chemical factors affecting selection of food plants by ruminants. In Phytochemical ecology. Proc. Phytochem. Soc. Symp. No. 8, p. 71-101. Academic Press Co., New York. Brown, E. R. 1961. The black-tailed deer of western Washington. Wash. Dep. Game, Biol. Bull. 13, 124 p. Olympia, Wash. Crouch, G. L. 1968. Forage availability in Donnelly, E. D., and W. B. Anthony. |