supported 1.2 5-2 times the number of deer that occurred. The 

 quantity of forage was adequate at all times, but the 

 nutritional quality of winter forage would not sustain deer at 

 any population level. The duration and severity of winter was 

 the factor determining the length of time that deer could 

 survive on these ranges (Wallmo et al. 1977). 



Studies in the Bridger Mountains of Montana (Mackie et 

 al. 1976, Hamlin 1977) indicated that what had been considered 

 the 2 "key" browse species on winter range supplied sufficient 

 forage to support less than one-third of the mule deer that 

 occurred. The remainder was provided by plants that had 

 previously been considered of poor quality or unimportant. 

 This situation had existed for years because plant density and 

 forage production had apparently not changed from prior years 

 when up to twice as many deer occurred on the winter range. 

 Total forage quantity was adequate, but nutritional level of 

 the winter diet was at maintenance levels or below (Morton 

 1976) . 



Harvesting to reduce the degree of use by deer on "key" 

 browse species in the Bridger Mountains would have required 

 reducing the deer population from about 200 deer to somewhere 

 below 60 deer. Similarly, utilization of rubber rabbitbrush, 

 a "key" forage plant in the Missouri River Breaks, was never 

 below 69 % and usually above 80% even at very low deer 

 population levels. As referred to earlier, trying to balance 

 winter deer populations with "key" species considered to 

 supply adequate quality forage will lead to the "ridiculous 

 conclusion that the only good herbivore population is one 

 vanishingly small" (Sinclair 1981). 



Where data are available for deer populations in northern 

 environments, summer forage has generally been shown to be 

 available in more than adequate quantities. In most cases, as 

 indicated by the studies cited above, the quantity of winter 

 forage also appears to be adequate, but its nutritional 

 quality is inadequate to support any deer for long periods. 

 The accumulation of fat reserves during summer and autumn, 

 winter growth dormancy by the animals, and behavior oriented 

 toward energy conservation are all strategies adopted by 

 northern cervids for the normal situation of nutritionally 

 inadequate winter forage (Klein 1985). Production and 

 survival of deer in these environments thus appears to be 

 influenced primarily by the length of time that deer can use 

 good to adequate quality forage, allowing them to accumulate 

 fat reserves. This is balanced by the length of the winter 

 period (or period of using low quality dormant forage) , and 

 the severity of the winter period as it determines energy 

 demand. 



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