Stand Basal Area 



Patterns of stand basal area increase are similar on all three plots [fig. 10). 

 Stand basal area growth rate gradually increases until the trees achieve virtually com- 

 plete dominance and then the rate of increase becomes constant. When the rate becomes 

 constant, the understory is reduced to a few plants that have negligible competitive 

 effects on the trees, and the stand can be considered closed. The constant rate of 

 basal area growth of closed stands is probably closely linked with site potential. The 

 growth rates prior to stand closure depend on density of trees and size distribution as 

 well as site potential. 



Obviously, there must be an upper limit on stand basal area and the rate of stand 

 basal area growth must decrease as this limit is approached. However, there is no in- 

 dication of such a decrease on these three plots. A slight decline in growth rate from 

 1975 to 1977 can be discerned in figure 10 and in some other figures, but this apparent 

 decline is attributed to unusually dry conditions during this period and to the fact 

 that the trees were cut and measured before they had completed their 1977 growth. 



Pinyon trees grow so slowly that several centuries may be required to reach the 

 upper limit on stand basal area. Few pinyon- juniper stands in the Great Basin are old 

 enough to be approaching this limit. 



40 I 1 



Year 



Figure 10. — Stand basal area on each of the ■plots from 1860 to 1977. 



14 



