5) Natural plant succession to a more closed canopy Douglas- 

 fir community. 



The first three impacts were related to the completion of the 

 Libby Dam project, while the other two impacts would have occurred 

 regardless of the project. 



Ccaistruction of Libby Dam and inundatioi of the impoundment 

 area directly removed approximately 11,000 acres of crucial white- 

 tailed deer winter range. This range consisted of bottomlands and 

 low benches the white-tailed deer historically relied on to furnish 

 necessary habitat components during periods of severe winter weath- 

 er. The project left a narrow belt of winter range along the edges 

 of the reservoir containing a limited supply of the necessary 

 habitat components. 



During successive years white-tailed deer have demonstrated a 

 tendency to use the same winter range within the impact area (Flath 

 1972a, Camj±>ell and Knoche 1974) , with similar results observed by 

 Mackie et al. (1980) in the Swan River valley. Inundation of 

 11,000 acres of winter range eliminated the traditional winter home 

 ranges for a large number of white-tailed deer. Loss of these home 

 ranges caused deer to be lost from the populations or disperse to 

 other areas, as evidenced by Flath (1973) who discovered a migra- 

 tion route along the border of the reservoir to Butler and Cody 

 creeks . 



Dispersal of white-tailed deer from inundated winter ranges 

 onto the remaining winter range increased the intraspecific compe- 

 tition for available habitat. Flath (1972a, 1972b) estimated den- 

 sities of 0.20 and 0.21 white-tailed deer/acre on the lower Fisher 

 River winter range during the winters of 1970-71 and 1971-72, 

 respectively (Table 2). These density estimates, for the two years 

 prior to inundation of the pool area, were below the long-term 

 average of 0.31 deer/acre (see page 23 of this report) , and indi- 

 cate some of the displaced deer could have been, at least tempo- 

 rarily, accommodated by the remaining winter range along the Fisher 

 River. However, the increased number of deer on the remaining 

 winter range would have produced increased use of the available 

 forage and depleted the forage supply available for survival during 

 severe winters. This probably resulted in increased competition 

 for the available forage during periods of severe winter weather, 

 with many deer succumbing due to reduced food availability and 

 poor nutrition (Hautz 1978). If the depletion of available forage 

 and over-utilization of the browse is of sufficient magnitude, a 

 longer term impact is created as the grazing capacity of the winter 

 range is reduced and a lengthy recovery is needed for the grazing 

 capacity to be restored to the previous levels. Although many of 

 the deer were probably accommodated on marginal range adjacent to 

 the reservoir, they were lost from the population during severe 

 winters. 



19 



