44 



BRITISH FOREST TREES 



Exclusive of timber extracted during thinnings, but includ- 

 ing branches below 2 '8 inches in diameter as well as timber, 

 the total average production of pure forest per acre is (in 

 cubic feet) approximately : 



A comparison of these various tables will show that although 

 on poor soil there is frequently more than double the 

 number of stems per acre that is to be found on soils of 

 the best quality, yet the growth in height and the growth 

 in girth are, up till near the eightieth year, each under the 

 half of that exhibited on the more favourable localities, and 

 though the proportion improves from the 80 i2oth 

 year, its advance is only slightly in excess of one half, 

 whilst the total production of wood exhibits very great 

 differences up till the end of the pole-forest stage, and at 

 no time amounts on inferior soil to half of that attained on 

 soil of the best quality. 



Great differences are exhibited according to soil and 

 situation by the various species of trees in regard to current 

 and average annual increment, as may be seen from the 

 following table exhibiting the total production of wood (in 

 cubic feet) : 



