YIELD. 45 



hundred years at least, approximate the capacity of our White Pine by reference to experieuoe 

 tables of the (lennaii Spruce. 



As with all couifers, the rate of productiou at first is very slow, not more than 4(1 to 70 cubic 

 feet in the average per year for the first twenty years. With the better development of crowns 

 and the assertion of individual superiority iu the struggle of neighbors, which leads to the estab- 

 lishment of dominant classes, the production increases rai)idly, and by the tiftieth year, in fully 

 stocked areas, the average rate of 140 to ItiO cubic feet per acre may be attained, so that at that 

 age we may, with five hundred to six hundred trees to the acre, find 7,000 to S,000 cubi(! feet of 

 wood stored up in the boles of the trees. The current annual accretion, then, may readily be at 

 tlie rate of IGO to ISO cubic feet, keeping the average annual accretion of fully stocked acres very 

 nearly to those figures, so that at one hundred years we should find, under favorable conditions, 

 as much as 15,000 cubic feet of wood, of which at least 80,000 to 00,000 leet P.. 'SI. is saw material. 



The persistency of growth seems to continue beyond that age, and the indications are that 

 the decrease of the current as well as average accretion per aci'e during the next century takes 

 place so gradually that at one hundred and fifty years it may still be over 100 cubic feet, and not 

 much below at two hundred years, when the burden of the acre may be near 20,000 cubic feet, 

 with over 120,000 feet B. M., and double the amount in the oldest growths of two hundred and 

 fifty or more years, which may possibly be the limit of production. 



While these figures, which differ very materially from those proposed in the tables by Messrs. 

 Pinchot and Ciraves, may stand for the better soils, as ideally possible, practically, perhaps, rarely 

 attainable, especially in older stands, poorer soil sites will vary from them by from 20 to 40 per cent, 

 so that a yield of 9,000 cubic feet at a hundred years, or 50,000 feet of lumber, would still be quite 

 reasonable to expect on the jroorest soils on which White Pine can be satisfactorily grown. On 

 the sandy soils of Wisconsin whole forties are found to average 50,000 feet per acre of naturally 

 grown unattended forests of one hundred and fifty years of age. 



Table VIII summarizes the measurements of sample areas, which are given in detail in tlie 

 Appendix.' It will serve to show what our native woods, without attention, stocked with partly 

 useless trees and in open stand, exhibiting much wastage in unoccupied ground, are capable of 

 producing. 



If we assume that the areas might have been stocked with pine alone, that they would have 

 produced at only the same rate as thej- have under their present conditions, even though the acres 

 had been fully stocked and not in the fractional manner which is indicated by the decimal giv- 

 ing density of cover (all assumptions), and if in connection with the density factor we consider 

 the number of all trees jier acre and the percentage which the pine represents, we may, as a mere 

 matter of judgment not fit for tabulation, arrive at au indication as to what the acre might 

 possibly have produced. Such indication of possibility has been attempted in the last column of 

 the table, and has served in the above discussion in connection with all other data presented. 

 This is all that can be done in the absence of the measurements above indicated. These figures 

 are of no direct practical apiilication except to give a general notion of the productivity of White 

 Pine and the variability of yields. 



An inspection of the table of yield in Germany, on page 69, will show that these approxi- 

 mations are not unreasonable. The lumber contents iu board feet may be approximated by 

 multii>jyiiig these figures by 4 or 5 in the younger growths and by G or 7 in the older. Assnining a 

 moderately careful practice of logger and sawyer, by no means mathematically tenable, the above 

 tentative propositions for normal yields might be even increased. 



To assume, as is done by certain authorities, that tables of normal yield could be constructed 

 by using the density indicated by a decimal as a matliematical factor, using that factor as a divisor 

 of the actually measured yield in order to arrive at the normal, is to mistake the value of the 

 density factor. Not only would trees and whole acres have developed very differently when grown 

 under different density conditions during their life, but the estimate of the density is such a vague 

 and uncertain one, a mere opinion, that even if the greatest care were exercised, its use as a mathe- 

 matical fixctor would not be admissible. It is a mere indication of the present condition of the 

 growth, and its meaning at different i)eriods of life is veiy different in its physiological effects 

 as exi)ressed iu volume accretion. 



