INTRODUCTION 



Aspen (Populus tremuloides) provide beautiful scenery and important wildlife 

 habitat on the Gros Ventre elk winter range of the Teton National Forest in north- 

 western Wyoming. Although aspen occupies only about 4 percent of the winter range, the 

 type usually is in a conspicuous position in the lower and middle elevations where it 

 often forms transition zones between shrub rangelands and conifer forests. Ecological 

 succession has not been satisfactorily documented for the Gros Ventre, but the aspen 

 type of the general area is now mostly considered as being serai to conifers and to have 

 been perpetuated by wildfire (Gruell 1970; and Loope 1971). Fires of the 1870' s and 

 1880' s are thought to have been particularly important in shaping the current vegeta- 

 tion, but more recently "...fire protection has allowed many aspen stands to be invaded 

 by conifer species" (Gruell 1970). Some 2,000 to 5,000 elk (Cervus canadensis nelsoni) 

 are thought to winter in the Gros Ventre area. Supplemental winter feed is supplied at 

 three Gros Ventre stations, but elk also feed on native trees, shrubs, sedges, grasses, 

 and forbs. Heavy elk use of aspen has, for several decades, been noted by the occur- 

 rence of "highlined" trees and browsed sprouts. 1 Elk and also moose (Aloes aloes 

 shirasi) apparently contribute to the conversion of aspen stands to conifers (Beetle 

 1968; and Gruell 1970). These animals cause injuries (fig. 1) that presumably induce 

 susceptibility of aspen to disease (Loope 1971) and they consume sprouts that might 

 otherwise replace dying overstory trees. In numerous stands, aspen are obviously dying 

 at an alarming rate (fig. 2). When conifers are absent, it appears that deteriorating 

 aspen stands will retrogress to a treeless rangeland type (fig. 3). 



The study described herein was initiated to provide an up-to-date prediction of 

 the future of aspen in the Gros Ventre area. Emphasis was placed on determining the 

 rate of mortality of the aspen overstory, its causes, and the likelihood of overstory 

 replacement by natural sprouting. Hopefully, these findings will inform resource 

 managers about the severity of the aspen deterioration problem so that they might better 

 determine whether modifications in current management might be necessary to maintain 

 the pleasing diversity of forest types now present in the Gros Ventre. 



inspection reports of Teton National Forest as relayed by George E. Gruell, 

 Wildlife Biologist, Teton NF, Jackson, Wyoming. 



1 



