260 CLARENCE F. KORSTIAN 



are secondary species. Juniperus utahensis and Pinus edulis 

 are found scattered through the brush, which clearly indicate 

 the potentiality of these ridge-tops and south slopes. In 

 northern Utah and southern Idaho Quercus gambelii is largely 

 replaced bj^ Ceanothus velutinus which is here indicative of 

 potential Pseudotsuga taxifolia sites. 



In central Idaho Purshia tridentata is found on the poorer 

 Pinus ponderosa sites. A tall, dense, luxuriant growth of 

 Physocarpus malvaceus, Ceanothus sanguineus, as well as the 

 presence of Vaccinium membranaceum, Rubus parviflorus and 

 Ribes viscosissimum are considered indicative of Pseudotsuga 

 taxifolia sites. 



Thorough scientific investigations should not only solve the 

 above problems but also should contribute much toward the in- 

 telligent selection of forest planting sites. Obviously, these 

 studies should also include a study of plant succession extending 

 over a rather long period of years. The natural variations or 

 succession of the native vegetation must not be forgotten. Wide 

 variations due to extraneous factors, such as fire, must also re- 

 ceive proper interpretation. Changes in the soil caused by fire 

 may also cause temporary differences in the character and dis- 

 tribution of native vegetation. It is contended by some that 

 plant indicator studies should be resolved eventually to terms 

 of the soil since the effect of site conditions is indicated by the 

 character of the subterranean parts of the native plants. This 

 is inadvisable because, as indicated above, we are really concerned 

 with the combined effect of the site on plant growth rather than 

 with the component factors. However, until the correlation has 

 been definitely determined, the soil and other important factors 

 should receive sufficient attention to enable a comprehensive 

 correlation of increment with the native forest vegetation and to 

 make proper deductions as to the relative importance of the 

 limiting factors. Plant indicator studies should also yield valu- 

 able data on the ecological relations of forest trees and their 

 associates. 



In conclusion, it is urged that, in the determination of site, 

 no one criterion should be adopted to the positive exclusion of 



