192 TRANSACTIONS OF ROYAL SC011TSH ARBORICULTURAL SOCIETY. 



their maturity, it is usually best to maintain close canopy overhead, 

 so as to prevent deterioration of the soil. 



Before interfering to any great extent with the density of a 

 pure crop of spruce or Scots pine, the trees should be allowed to 

 have attained their main growth in height. Always try to get 

 them to grow high first, then let them thicken in girth afterwards. 



While it may be taken that in most districts the first thinnings 

 from young plantations are of little or no money value, the later 

 returns from these must by no means be underestimated. 



Unfortunately we have as yet no reliable average returns of 

 what may be expected from thinnings in British plantations grown 

 for profit and on a definite rotation. Hence we must still look to 

 the Continent to see to what general extent thinnings m.ay be 

 expected from crops of normal density for any given kind of tree. 



In a conifer wood to be felled at ninety years of age, thinnings 

 may be assumed to take place every ten years after the plantation 

 is twenty-five years old, and Burckhardt's yield tables for Hanover 

 furnish useful data as to the number of cubic feet which may be 

 expected as thinnings before the final crop is cleared. 



Where the soil is good, and where the crop is of normal density, 

 he reckons that the thinnings from pure spruce woods would give 

 an annual average yield of 30 cubic feet per acre, or a total for 

 thinnings alone of 2700 cubic feet (true cubic contents) per acre. 

 This is equal to 2120 cubic feet square-of-quarter-girth measure- 

 ment, which at 3d. per cubic foot is worth ^26, los. in all. 



The number of spruce trees growing on an imperial acre at 

 ninety years of age may reasonably be calculated at 280. 

 Each of these would average about 16 cubic feet, or a 

 total of 4480 cubic feet of timber as representing the final yield, 

 the money value of which may be moderately estimated at 

 4|d. per cubic foot, or ;!^84 in all. This sum added to the 

 value of the thinnings brings the total returns for ninety years 

 up to ^iio, los. per imperial acre. Estimating the cost of 

 fencing, draining, and planting, etc., at ^5, 13s. gd., and the 

 tending, management, and payment of rates and taxes at 3s. 

 per acre per annum, this leaves a net average annual revenue of 

 about 23s. 3d. per acre, although, of course, the only proper 

 method is to prolong all the items (except the value of the final 

 yield) at compound interest up to ninety years of age. 



From a pure Scots pine plantation grown on suitable soil, the 

 average annual returns are slightly more favourable. Taking 



