760 JOURNAL OF FORESTRY 



natural basis of all for comparing the growth of different species on 

 the same site, as well as for identifying sites containing trees of the 

 same species but of different ages. 



In conclusion, the principle of height growth as a guide to site has 

 the following features : 



1. It is simple, natural, easily understood, and easily applied in the 

 field. 



2. It is independent of the determination of physical sites producing 

 definite permanent forms of forest ; but the tw^o are not antagonistic ; 

 both are "indicators" and both demand equally a determination, more 

 or less refined, of the physical factors of site. 



3. The sites determined by height growth are species sites, not per- 

 manent type sites ; hence they are useful with reference to short-lived 

 intolerant and to long-lived tolerant species growing in the same stand. 



4. By adopting one or more index species (intolerant species of wide 

 occurrence on a variety of sites) the height growth of other species 

 can be gauged, their relative value in each site can be determined, and 

 this value can be expressed by naming the site in terms of the growth 

 of each species present and by analogy of other species which do not 

 happen to be present. 



5. It affords a means of comparing the growth of all American spe- 

 cies on the basis of the soil and climate to which each is best suited, as 

 well as in less favorable sites. 



6. It permits a ready comparison (a ) between even-aged second-^ 

 growth stands in widely different regions, thereby avoiding such incon- 

 sistencies as those to be found in the published yield tables for the 

 same species in different states, and (b) between second-growth and 

 old-groM'th stands in the same or dift'erent regions. 



7. Since height growth is sensitive to interferences in the natural life 

 of the stand (fire, culling, changes in density, etc.), care and judgment 

 are necessary in the choice of trees to serve as the index ; but, except 

 for very precise site determinations, the method, if used with ordinary 

 caution, will undoubtedly prove serviceable for the majority of wild- 

 woods conditions as well as for even-aged stands. 



8. As the knowledge of the laws of growth of our species increases, 

 the refinement of site determination by height growth can be increased. 



Finally, if it accomplishes nothing else than to stimulate our efforts 

 to learn the progress of growth of our species and the laws determin- 

 ing it, their proposed system of classification will have served a great 

 purpose. Its greatest possibilities lie, however, in the direction of a 

 workable classification within a reasonable time. 



