558 JOURNAL OF FORESTRY 



3. As the growth conditions of regions are often well marked, and 

 as the growth of the individual trees is well marked, the range of figures 

 from the greatest to the least may be conveniently divided into groups, 

 the groups to represent regions or species. 



4. The groups should be subdivided in such a way that each sub- 

 division will represent a natural site distinction. It would be confusing 

 to divide that group which represents the rapidly growing trees of the 

 north Pacific Coast into sites which differ only by 10 feet, since in that 

 region two trees, although of the same species, dominance, age, and 

 growing on similar sites, may have a variation of that much in their 

 height. Similarly, it would be confusing and incorrect to divide that 

 group which represents Arizona into sites which differ by twenty-five, 

 inasmuch as 25 feet might cover the actual difference in the heights of 

 tree on two or more sites. A consistency must be kept between the 

 sensitiveness and the value of the criterion of site and the number of 

 sites in the group. 



The result of these principles is a division of the growth conditions 

 of the country into groups of similars, and these groups are divided 

 into natural arbitrary divisions which represent the individual sites of 

 the group. 



The system of classification given below is frankly patterned after 

 that system advocated by Roth in his article in the Forestry Quarterly, 

 March, 1916. Mr. Roth divides the trees of the country into three 

 groups, as determined by their growth in height; the present system 

 uses six groups, Mr. Roth's division of the groups into four sites is 

 adopted here. 



The following is the system of site classification advocated : 



Heights of Dominant Trees at 100 Years of Age Height at 40 Years 

 Sites Group A Group B Group C Group D Group E Group F 



I 150 125 100 75 50 75 



II 125 105 85 65 45 65 



III 100 85 70 55 40 55 



IV 75 65 55 45 35 45 



In the above system Group A includes the Douglas fir, western hem- 

 lock, and Sitka spruce of the Pacific Coast. 



Group B will include the sugar pine, white fir, and western yellow 

 pine of the west side of the Sierra Mountains of California. It will 

 also probably include some of the loblolly pine of the South. 



Group C will include the jack pine of the Lake States, white and 

 Norway pines, longleaf pine, and, in some regions, western yellow pine. 



