28 BULLETTlSr 418, U. S. DEPARTMENT OF AGRICULTURE, 



the reserved trees v/as found to be very large. On seven sample plots 

 wliich were studied intensively it amounted to 310, 219, 242, 141, 103, 

 63, and 48 per cent, respectively. On these areas the increase in the 

 growth rate was in inverse relation to the volume of the reserved trees 

 on the sample plot. Where there were many trees left standing there 

 was less stimulation than where there were few. The acceleration 

 in growth was also more noticeable where the reserved trees were 

 evenly distributed than where they were crowded into groups. 



The measurement of a similar area in Klamath County lightly cuUed 

 over some 24 years ago, on wluch "bull pines" and somewhat mis- 

 shapen older trees were left, showed the increase in the growth of 

 these reserved trees to have been surprisingly large since the thinning 

 was made, amounting in one sample plot ^ to 105 per cent in the 

 volume growth, and in another^ to 63 per cent in the basal area growth. 



Yellow pine's rate of growth responds quickly to changes in the 

 soil moisture, soil depth, aspect, climate, density of the stand, etc. ; 

 and the changes in these factors are very frequent in the mountainous , 

 country such as yellow pine inhabits. Within the Blue Mountain 

 region alone, on neighboring tracts (Winlock's Mill and MiU Creek) 

 both of which support typical commercial yellow-pine stands, the 

 volume growth of a 190-year-old tree is in the one case 3.7 board 

 feet per year, and in the other 9.0, a range of 240 per cent. 



STANDS. 



It is easy to determine the rate of growth of individual trees, but 

 extremely difficult to find out, even approximately, that of stands, 

 especially when only uneven aged and virgin forests which are irregular 

 in density are available for measurement. Theoretically, and ac- 

 tually on large areas, there is no net growth in the virgin forest; i. e., 

 the growth of the living trees is just offset by the death of occasional 

 old ones. Young trees take the place of the dying ones just rapidly 

 enough to preserve indefinitely a uniform volume. Assuming that 

 no trees died, the growth on an acre in such stands as those listed in 

 Table 7 would probably be 100 board feet or more per year on average 

 soils, and fully 200 feet on good soils.^ 



The forester, however, is particularly interested in the rate of 

 growth that he can secure on lands that have been cut over under 

 proper regulations. Until there is an opportunity to remeasure 

 sample plots in areas which have been cut over, exact yield data of 

 this character will be lacking. Estimates based upon the gross 

 growth of virgin forests, which take into consideration the several 



1 Manuscript report, " Silvicultural Aspects of Cutting in Open Yellow-Pine Forests," by H. D. Foster, 

 forest assistant. 



» Manuscript report, "Notes Regarding Increased Growth la Yellow-Pine Stands as the Result of a 

 Selection Cutting," by Thornton T. Munger, forest assistant. 



» Growth rate of individual trees as shown in Table 11. 



