450 COORDINATION OF FOREST SURVEY 



predictions for the forest. Wherever possible, this division must be 

 made. 



348. Growth on Areas of Immature Timber. The growth on any 

 large area, whether the form of forest is even-aged in pure stands, or 

 many-aged in mixed stands (§ 314) must include that of the young, 

 unmerchantable stands. This growth is a prediction of future volume, 

 and as such, may be obtained, not by measuring the present volume 

 of the stand, nor by counting the number of trees in very young stands, 

 but by the method of comparison with older stands. The yield table 

 based on area and age gives this comparison. But to utilize the table, 

 the one thing necessary to determine is the area which is stocked with 

 the immature timber. Its age is more easily determined than for old 

 timber, either by cutting or by counting whorls. Based on area and 

 age, the future yield is a matter of density of stocking. The rate of 

 growth per year may be taken as the mean annual growth, shown 

 by the reduced or empirical yield table, for the age at which the stand 

 will be cut. 



The density per cent for young stands is practically independent 

 of the density of crown cover, and depends instead upon the number 

 of trees per acre as compared with the normal number required at 

 maturity, the distribution of these trees over the area, and the chance 

 of survival (§316). Mortality in scattered stands where each tree 

 has room to grow is much less than in crowded stands; and if the 

 spacing of the reproduction is such that, allowing for a reasonable 

 rate of loss from insects and causes other than suppression, the stand 

 will reach full stocking at least a decade before maturity, it can be 

 considered as fully stocked now. 



If a large area is being measured and an average density per cent 

 is found for this area, resulting in an empirical yield table somewhat 

 lower in values than the normal table, a conservative plan is to assume 

 that the ultimate yield of young stands will not exceed this density, 

 and to use the empirical yield table as the basis for calculating their 

 future yields. 



That area and yield per acre is the only possible basis of prediction 

 of yield for immature stands must become evident by considering the 

 difficulties of the opposite plan, that of counting numbers of trees on 

 snail plots. In tallying or counting reproduction or immature sizes, 

 it is customary to lay off the plots at fixed intervals, comprising from 

 one-tenth of the estimated strip, down to less than 1 per cent of the 

 strip, and to count the seedlings and saplings upon these plots. The 

 only way in which these data can be used to predict growth on such 

 small timber is by predicting the percentage of this count which will 

 survive. The method of comparison by numbers of trees is useless, 



