184 ORUANISATION OF SELECTION- WORKED F0EEST8. 



Iq determining the yield of Selection Fellnigs, i. e. the 

 number of trees to bo exploited eaob year, the Amenagiste may 

 either allow himself to be guided by the figures of the previous 

 exploitations or by the number of exploitable trees actually stand- 

 ing on the ground. For example, if anterior to the organisation of 

 the forest the number of trees felled annually is 4 for every 5 

 acres, he must either maintain this figure or raise or diminish it 

 according as he finds the forest well-stocked, overstocked or under-. 

 Btocked as regards large trees. This be could not know, with the 

 certainty necessary for the work in hand, except by studying close- 

 ly the various crops, noting the annual increment of the trees that 

 are near the exploitable dimensions, and, lastly, reviewing the 

 results of the valuation survey of all the formed trees of the 

 forest arranged into size-classes. If the yield of the previous 

 (Selection Fellings cannot be ascertained, the production of the soil 

 per acre must serve as a guide. The amount of this production 

 -ean generally be estimated with sufijcient approximation by men 

 well up in the forester's craft ; those who have had much to do 

 with the exploitation of forests easily acquire this faculty. Moreover 

 it may be obtained in various other ways, by an actual valuation 

 survey, for instance, of, the standing material in judiciously select' 

 ed canopied masses of trees of the same age. 1 



(1.) The study of the growth of trees also enables us to estimate the produc- 

 tion of the soil in exploitable timber. Suppose, for instance, we have a forest 

 in which healthy trees may be expected for certain to attain a diameter of 

 24 inches. Suppose also that the average annual radial increment has been 

 found, by means of measurements made on felled timber, to be one-tenth of 

 an inch. Hence it would take 60 years for a tree of 12 inches diameter to 

 attain a diameter of 24 inches. The time required for a tree to reach a diame- 

 ter of 12 inches, rarely the same for any two trees even of the same crop 

 might be on the whole much longer than 60 years. If we suppose it to be half 

 as long again, i. e. 90 yeai-s, then the time required to obtain trees of 24 inches 

 diameter would be 150 years. In the next place those portions of the forest, 

 in which several trees of this size are found grouped together, show how many 

 of them could stand on an acre completely stocked with them. Say that this 

 number has been found to be 75. From the preceding data may now be 

 .calculated the total annual sum of production per acre in mature timber. 

 Thus it might be half a tree per acre per annum, measuring from 50 to 70 

 cubic feet according to the height attained by the trees. 



The known yield of adjoining forests growing under similar conditions and 

 under systematic treatment would also furnish a safe guide. 



These various methods can be used to check one another, but their applies' 

 tion requires no liltls experience on the part of the Am^uagjstg. 



