AGE IN EVEN-AGED VERSUS MANY-AGED STANDS 325 



This problem may be illustrated as follows : 



A stand of pine has now 10,000 board feet per acre. The growth for ten years 

 upon the trees which will survive will be 4000 board feet. The trees which will die 

 in ten years have now a volume of 1500 board feet. This means, first, that the 

 growth of 4000 board feet is actually put upon a present volume of 8500 board feet; 

 second, that the remaining 1500 board feet must either be included in or deducted 

 from the final yield, on the basis of whether it is actually salvaged or not. There 

 may have been some growth on these trees, but this can be neglected. On the assump- 

 tion that no cutting of thinnings is possible, the net yield on this acre at the end of 

 the decade is 12,500 board feet. If thinnings are harvested, the yield is 14,000 board 

 feet. Had the growth prediction been attempted by measuring the growth of indi- 

 vidual trees, those representing the 1500 board feet would have to be excluded from 

 the calculation of total growth in either case. Unless salvaged, they represent an 

 actual negative growth reducing the net gain by 1500 board feet. 



Unless it is possible to guess just how many and which trees are 

 going to die, not only the volume, but the growth for ten years on some 

 of these trees wiU probably be erroneously included, instead of being 

 subtracted from the predicted total yield in ten years. The possible 

 error in subtracting either too few or too many trees is very large 

 since the size of the eiTor is doubled for stands when thinnings are 

 impractical. It is obvious that a method depending instead on direct 

 measurement of the result at the end of the period on older stands 

 and the comparison of such measurements with similar younger stands 

 furnishes a safer basis of growth predictions on these younger stands 

 for any considerable period than efforts to project into the next period 

 the rate of growth of the trees now standing. 



Where stands are under intensive management, the trees which 

 will die are thinned out, probably at the beginning of the period, and 

 utilized. The loss for the succeeding ten-year period is then exceedingly 

 small unless accidental im-oads occm- from wind, insects or other destruc- 

 tive agencies not anticipated. It is therefore safer to predict growth 

 for short periods on stands which have been under management and 

 have been thinned than it is on stands where thinnings and utilization 

 of the dying material is impossible. 



253. The Factor of Age in Even-aged versus Many-aged Stands. 

 Where stands are measured as a unit to determine the production per 

 acre, three factors are needed: first, the present volume of the stand; 

 second, its average age or the time which it took to produce this volume; 

 third, the area which it occupies. The age of the stand as a whole 

 is desired. If the stand is even-aged it is sufficient to determine merely 

 the age of one of the trees adequately to measure the period of pro- 

 duction and the rate per year. This can be done by counting the annual 

 rings of growth without any measurement whatever, on the assumption 

 that the species has formed but one annual ring per j'ear. This premise 

 does not always hold good, since with certain species in certain localities, 



