376 JOURNAL OF FORESTRY 



was left as it tell. Plots 3 and 4 were logged in 1909, plot i in 1894, 

 and plot 2 about 1895. 



Only two site qualities have been recognized, although detailed 

 studies would doubtless reveal minor variations. Plots i, 2, and 3 are 

 very similar and lie within a few miles of each other. All are char- 

 acterized by a gently rolling topography and a clayey soil of basaltic 

 origin mixed with basaltic rocks of various sizes. The mean annual 

 precipitation is around 23 inches. The altitude is close to 7,200 feet. 

 Plot 4 is distinguished from the others by the presence of a surface 

 layer of black volcanic cinders varying from one inch to a foot or more 

 in depth, the underlying soil being generally similar to that on the first 

 three plots. This plot also lies at a slightly lower altitude and prob- 

 ably receives several inches less precipitation than the others. 



The acreage, exclusive of "intensive" plots, is as follows: Plot i, 

 243 acres ; plot 2, 135 acres ; plot 3, 456 acres ; plot 4, 304 acres. 



RESULTS 



The results from "intensive" plots which deal with individual trees 

 are for the most part omitted in this article, because the period of 

 observation is too short to give reliable data of this character. For 

 example, diameter measurements on individual trees for short periods 

 are greatly affected by irregularities in the bark; height measurements 

 taken with a hypsometer are apt to be from i to 2 feet in error; 

 volume calculations based upon volume tables will be inaccurate be- 

 cause the individual tree departs more or less from the normal rep- 

 resented by the volume table. These irregularities will decrease as the 

 period increases, although in the case of volume they must continue 

 to be reckoned with. When the results deal with averages for a large 

 number of trees, as in the "extensive" plots, inaccuracies of the char- 

 acter mentioned are apt to be relatively small, even when the record 

 covers a period as short as 5 years. It is therefore felt that the data 

 presented in this article, based almost entirely upon "extensive" plots, 

 may be accepted as trustworthy when applied with a proper under- 

 standing of their limitations. 



As has been previously indicated, distinction is made between black 

 jack, or young trees, and yellow pine, or old trees. Black jack grows 

 more rapidly, has a greater taper and lower form factor, and usually 

 contains a lower proportion of merchantable material than yellow pine. 

 Although the two classes are always distinguished in timber-sale prac- 

 tice, a clear line of demarkation is difficult to establish because the 



