18 FORESTRY BRANCH BULLETIN NO. 33 



grass-land is very poor in quality and that condition is not one to be regarded very 

 favourably, because the maintenance of tree growth would keep the productive capa- 

 city of the land greater. 



INFLUENCE OF DENSITY. 



The chief disadvantage of the present condition of second-growth stands is their 

 too great density. This is a serious disadvantage, especially in the pine stands. Pine 

 seeds up very thickly after fires and its tolerance is sufficient to prevent a rapid 

 decimation of the young trees, and so many trees remain alive that none are able 

 to develop rapidly into large-sized material. Thinning would be an effective remedy; 

 and where fence-posts, fuel, &c., are in demand, it might be carried out on a small 

 scale: but with the vast majority of second-growth stands, it will be necessary to 

 wait the extra length of time necessary to the development of useful material. 



The normal number of trees in second-growth stands varies, of course, with site 

 and age. On Sites I and II, where the soil conditions are fairly good, differences in 

 rates of growth do not become marked until after fifty years, so that average figures 

 can be given for the two sites up to that age. About 1,000 trees per acre, one inch 

 and over, is normal at fifty years, and at that age the dominant trees are about eight 

 inches in diameter, and forty to fifty feet high. At twenty-five years, the same stand 

 would have had about 1,500 trees. In dense stands, a larger proportion of the trees 

 are in the suppressed class than where the total number per acre is smaller. In a 

 plot with 3,000 trees per acre, there were 1,400 dead suppressed trees. That indicated 

 a very high density in early youth. 



The following table of normality is used by reconnaissance parties in lodgepole 

 pine forests in Montana. It aims to give quantitative expression to the effect of 

 over-stocking on the yield, similar- to that of under-stocking. 



TABLE 4. 



TABLE OF NORMALITY. 



In practice a plus sign (e.g., 0-9+) is placed after the figure of normality to 

 indicate over-stocking, rather than under-stocking. 



In mature stands, the variation in diameter resulting from different densities 

 is marked. Among fourteen plots, those three having trees of the largest average 

 diameters had the smallest total number of trees. The remaining plots, when 

 arranged according to density, showed successively decreasing diameters. Since the 

 range of average diameters was only from eight inches to twelve inches and the 

 minimum size of merchantable trees lies between eight inches and ten inches, it 

 is apparent that a small variation in the average diameter makes a very great 

 difference in the number of trees merchantable. Also, the merchantable contents of 

 trees and the value of the material obtained increase relatively very rapidly with 

 increase in diameter. 



From a consideration of sample plots, it would appear that the maximum density 

 of mature stands consistent with proper development lies between 400 and 600 trees 

 per acre, three inches and over, of which only 200 to 250 trees would be over eight 

 inches. The optimum lies in the neighbourhood of 300 to 400 trees per acre. 



