Figure 8. — Big game soars 

 on a 9 -inoh- diameter 

 aspen trunk. The fresh 

 toothmarks near the 

 center and tower right 

 of this late-summer 

 photo are suspected to 

 have been made by a 

 moose. The scar on the 

 upper left likely was 

 from elk chewing of the 

 previous winter and 

 that on the right from 

 elk a year earlier. 



Unfortunately, mortality tends to open the crown canopy which can initiate a chain 

 of events that result in rapid stand deterioration. Graham, Harrison, and Westell 

 (1963) noted that deterioration following the opening of aspen crown canopies can some- 

 times render "...within a 5- or 10-year period a valuable stand... to a worthless 

 condition." Presumably, increased exposure to sunlight and associated sunscald that 

 results from opening the canopy increases the susceptibility of remaining trees to harm- 

 ful insects and diseases. This is an alarming hypothesis for the Gros Ventre elk winter 

 range where most stands of aspen are already in at least the early stages of deteriora- 

 tion. It also seems reasonable to suspect, as Beetle (1968) suggested, that remaining 

 trees become more "vulnerable to wind" as stands are opened up through overstory 

 mortality. 



It should not be overlooked that some mortality in a relatively dense aspen over- 

 story might improve wildlife habitat by increasing forage production in the understory. 

 Concerning the Coconino National Forest, Reynolds (1969) reported that thinning aspen 

 from 229 sq.ft. basal area per acre to 42 sq.ft. per acre significantly increased the 

 production of forbs , perennial grasses, and aspen sprouts. In the Gros Ventre, live 

 aspens averaged only about 138 sq.ft. per acre in the 1970 plots, but 16 percent of the 

 plots had less than half that amount. Natural mortality seldom resulted in fallen trees 

 in numbers sufficient to create barriers to animal movement such as Reynolds had noted 

 and it is assumed that increased forage is readily available to big game. 



14 



