The quantity of forage available on the study area during 

 winter and spring was not directly measured, however some 

 observations indicated that it was unnecessary. Forage 

 quantity or quality probably was not limiting during spring 

 (April- June) because more green forbs were available then than 

 during July when plots were clipped (Table 3.3). Also, deer 

 made considerable use of ubiquitous new green grasses during 

 spring. 



The primary forage species used during winter (big 

 sagebrush and Rocky Mountain juniper) were essentially 

 unlimited in abundance. No hedging, highlining, or other 

 indications of overuse of those species was noted. As pointed 

 out by Wallmo et al. (1977), the total use of those species 

 may be limited because of the bacteriocidal effects of their 

 essential oils. Substantial use must be made of other species 

 to dilute big sagebrush and Rocky Mountain juniper. Although 

 most other forage available during winter, with the possible 

 exception of rabbitbrush, were nutritionally below maintenance 

 requirements for deer, adequate quantities were available to 

 mix with big sagebrush and Rocky Mountain juniper. 



Rabbitbrush was essentially used entirely every year, 

 even at the lowest observed deer densities. At low deer 

 densities, however, it may be available for a longer portion 

 of the winter period, raising the average nutritional plane of 

 deer. 



Regardless of deer density, forage quantity appeared to 

 be adequate, but forage quality, by itself, was probably 

 inadequate, to sustain deer during any winter. Although 

 winter forage supplied a portion of maintenance requirements, 

 winter survival appeared to depend on fat accumulation and 

 storage during summer and autumn, the length and severity of 

 winter, and energy conservation behavior (Wood et al. 1962, 

 Loveless 1967, Silver et al . 1969, Thompson et al . 1973, 

 Bucsis 1974, Short et al. 1974, Mackie et al. 1976, Mautz et 

 al. 1976, Walmo et al. 1977, Mautz 1978, and Youmans 1979). 



Changes in Abundance and Use of Forage Plants 



The percentage of current annual growth twigs or 

 "leaders" on shrubs used by mule deer was recorded each year, 

 beginning in 1959 for rubber rabbitbrush and 1960 for fragrant 

 sumac (Fig. 3.10). These 25 plant transects were established 

 according to the criteria of Cole (1958 and 1959) and 

 originally included information collected on age, condition, 

 and form class of the plants, as well as percent leader use. 

 Transects were measured in spring of each year and, thus, 

 recorded use for the previous summer, autumn, and winter. 

 Although Mackie (1975) determined that these transects did not 



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