DISCUSSION AND CONCLUSION 



Since aspen generally are known to be short-lived trees (Strothmann and Zasada 

 1957), it is natural that some aspen stands are becoming decadent in the Gros Ventre. 

 Meinecke (1929) noted for nearby Utah that senility occurs with aspen at about 120 

 years of age and that the "wild aspen forest as a whole does not reach much beyond 

 130 years." If this is true for the Gros Ventre, we can expect a marked change in 

 much of the aspen type within the next few decades since about two-thirds of the 

 sampled trees are already in the 81- to 120-year age class. Furthermore, a drastic 

 decline in the aspen type is eminent if game browsing continues to prohibit replacement 

 of dying overstory trees and if exclusion of fire continues to allow invasion by 

 conifers . 



Even if the aspen senility and decadence situations of Utah do not apply directly 

 to the study area, the Gros Ventre mortality data (see page 6, second tabulation) 

 provide a dismal view. Using those data we can estimate that in 1970 there were 

 approximately 1,500,000 aspen trees in the 3,330 acres of aspen type in the Gros Ventre 

 sample area. If the 3.6 percent mortality rate of 1970 remains stable in the future, 

 aspen would decline to about 500,000 trees by year 2000, and to only 40,000 by year 

 2070. Although the 3.6 percent rate was a fair estimate 3 based on the criteria used 

 to estimate current year mortality, it probably was conservative since it could not 

 have included trees which died in 1970 during winter dormancy. Certainly, these data 

 indicate that unless there is replacement of overstory trees, the aspen overstory is 

 due for a marked decline. 



Although few comparative data are available, aspen mortality appears to be somewhat 

 greater on the Gros Ventre than in other aspen areas. For instance, Hinds (1964) found 

 that only 9 percent of the standing trees were dead in sample plots scattered over a 

 wide area of Colorado, whereas almost 42 percent in the Gros Ventre sample were dead. 

 Assuming that most aspen trees remain standing for about 10 years after death (which 

 approximates the measured 1970 Gros Ventre mortality rate), there appears to be less 



3 The confidence interval at the 0.05 level was only 2.6 to 4.6 percent as deter- 

 mined from a standard error computed as described by Freese (1962) for attributes from 

 unequal-sized clusters. 



L2 



