40 



THE COMMERCIAL HICKORIES. 



YIELD. 



Yield tables show how much wood a given species will produce to 

 the acre at different ages. In connection with tree values, these 

 tables enable the intelligent woodlot owner to tell what trees it will 

 pay him best to grow. Longleaf pine, for instance, produces a 

 stronger and more valuable wood than loblolly pine and has the 

 additional advantage of producing resin in merchantable quantities, 

 but it is slower growing, and the yield per acre at the end of fifty or 

 eighty or one hundred years is less than that from loblolly. Conse- 

 quently he regards the loblolly as the better tree, and on soils which 

 are suited to it he favors it over the longleaf. Similarly, conifers, 

 such as pine, spruce, and Douglas fir, are a more profitable crop than 

 broad-leaf trees, such as oak, ash, and black walnut, because their 

 greater yield more than offsets the lower value of the wood. The 

 yield per acre per year, under similar conditions of soil and climate 

 and in stands of equal age and density, should be constant for a 

 given species and often will differ greatly from that of other species^ 

 The determination of yield is of most importance for trees, such as 

 pine and spruce, that grow naturally in pure, even-aged stands, but 

 even in the case of hickories, which usually grow in mixture with 

 other species, computations of yield per acre offer comparisons with 

 other species and indicate how well the hickories utilize the space 

 which they occupy. 



In computing yields it is necessary to know^not only the size of 

 the trees, but also how many there are per acre. The best way to 

 determine these two points is by actual measurement of pure, even- 

 aged stands of different ages. Such measurements of 30 plots, with 

 an average area of one-fourth acre, in several regions and for various 

 species, showed the average yields of pure, even-aged stands of 

 hickory at different ages to be as given in Table 14. 



TABLE 14. Average yield of hickory per acre. 



It will be noted, first, that the average diameters, except during 

 the earlier years, fall below those given for shagbark and pignut in 

 Table 4. This is because the stands in many cases were too dense, 



