THE DOUGLAS FIR IN SCOTLAND. 



229 



Volume of sample tree : volume per acre = sectional area of sample 

 tree: Sectional area of all trees per acre; or 17'89 : a; ="757: 



17-89 X 158-17 



158-17, and a; = volume per acre: 



•757 



= 3738 cubic feet 



of solid wood over 3 inches in diameter, exclusive of top and branches. 

 By dividing the volume by the age of the trees (32) the average 



annual production of wood is obtained : =117 cubic feet, 



exclusive of previous thinnings ; or, if only the time since planting 

 (28 years) is taken into account : — Average annual production of 



solid wood= __ = 133 cubic feet, exclusive of previous thinnings. 



28 



By way of comparing these results with the production of one 

 of our indigenous trees, I measured the trees on a sample plot of 

 one-tenth of an acre — in a very uniform plantation of Scotfe pine, 

 situated at a short distance from the Douglas fir plantation. This 

 Scots pine plantation had been established in a somewhat elevated 

 spot, which was formerly of a swampy description. The locality 

 must be classed as of second quality only, compared with the 

 locality in which the Douglas firs grow. It was drained and 

 planted in 1847 — that is forty-one years ago — with four years old 

 plants of Scots pine ; it has been thinned three times, and it will 

 again be thinned in 1889. On July 20, 1888, the area was fully 

 stocked. Omitting all suppressed trees, the survey yielded the 

 following results : — 



It will be noticed that this plantation shows a greater sectional 

 area per acre than the Douglas fir plantation. 



The mean height of the wood was found to be 45 feet, and from 

 the available data it was ascertained that the volume of solid wood 

 (3 inches diameter and upwards) amounted to 5015 cubic feet per 

 acre. By dividing this number by 45 — the total age of the trees, I 



