CONCLUSIONS 



Since the data were obtained on only three plots in a single area and do not in- 

 clude juniper, the results obtained in the Sweetwater area may not apply to pinyon- 

 juniper stands throughout the Great Basin. Pinyon- juniper stands in central and eastern 

 Nevada will be examined in a similar manner to broaden the data base and extend the area 

 of applicability. However, the Sweetwater results suggest a number of characteristics 

 of singleleaf pinyon trees and stands that may be common throughout the range of this 

 species with or without juniper association. These characteristics are as follows: 



1. Height growth of dominants and codominants appears to be little affected by 

 age or competition. Height growth rates of dominants and codominants generally remained 

 constant during most of their lives; the only trees that were found to be approaching 

 culmination of height growth were those trees that were severely suppressed. 



2. Height growth rates can vary significantly among dominants on the same plot. 

 Differences in height growth of dominants may be due to genetic variation. These dif- 

 ferences appear to be linked to growth form; height growth is generally slower in trees 

 that have a shrubby form and multiple leaders. 



3. Diameter growth rate is regulated by competition rather than by age. 



4. The rate of increase of stand basal area becomes relatively constant when the 

 trees dominate the site. The rate of basal area increase of closed stands may be an 

 accurate index of site potential, providing the stand is not decadent. Truly decadent 

 stands are probably very rare in the pinyon- juniper type. 



5. The increase in total above-ground biomass approaches a constant rate after 

 the trees fully dominate the site. Eventually the rate of biomass increment must de- 

 crease but there was no indication of an impending decrease on the three plots in the 

 Sweetwater study area. The rate was still increasing on two of the plots. Pinyon trees 

 grow so slowly that maximum biomass may not be attained for several centuries. The data 

 suggest that growth rate is essentially constant until the maximum biomass is approached. 



19 



