84 



Proceedings of the Royal Irish Academy. 



24 inches in diameter ; basal area, 83 square feet per acre : volume of timber 

 206 cubic feet per acre. 



The differences in height, diamet€r, and volume observable in these two 

 young plantations, which are both in perfect health, correspond with what is 

 recorded of mature trees in their native forests. In the Oregon Douglas 

 Fir plot all the grass and undergrowth have been killed, while in the other 

 plot some bracken and bramble still survive. The needles of the Oregon 

 species appear to decompose much more quickly than those of the Colorado 

 Douglas Fir. Thus, though the total leaf-fall of the former must have far 

 e.xceeded that of the latter, the foliar debris on the ground was only ] finches 

 deep in the Oregon Douglas Fir plot, while it was 2 inches deep in the other 

 plot. There is much less humus in the surface soil under the Colorado 

 species than there is under the Oregon species. 



The Oregon Douglas Fir is one of the most valuable trees that have been 

 introduced. It proiUices in this country an enormous volume of excellent 

 timber in a short period of time, being rea<iy for felling at fifty or si.xty years 

 old. Grown in dense plantations, it surpasses all other species in yield of 

 timber. 'J'his great production is shown by the following table,' which gives 

 actual measurements of plantations of Oregon Douglas Fir in Scotland, 

 England, and Wales. These plantations have not been selected in any 

 way ; and some of them, owing to errors in initial planting and subsequent 

 thinning, are insuthciently stocked, and show poorer yields than may be 

 e-xpected from plantations grown under better methods of silviculture. 



EAatc and Counlj. 



Age. 



Number of 



tree* 

 per acre. 



Mean lieight 



of dominant 



tree*. 



Volume of 

 timber 

 per acre 



over bark. 



Arerage 



annual 



growth 



in volume 



per acre. 



tUgler, Oxford, 



Tean 

 12 



No. 

 2132 



Feet. 



32 



Cub. ft.* 

 923 



Cub.ft.* 

 77 



Llandinam, Montgomeiv, 



■2» 



347 



66 



6663 



109 



Toftworth, 01ouce»ter, 



■I•^ 



206 



66 



3690 



127 



Duniter, Sooienrt,. 



33 



350 



71 



1975 



151 



Tort»orth, Gloucetter, . 



43 



215 



97 



7316 



170 



TarmoanI, Perth, . 



52 



119 



88 



6640 



128 



Cochvillan, Camarton. . 



58 



119 



101 



11080 



ISO 



* Quarter-girt meaiurement. 



The Reconstruction Forestry Report, making a reduction of 30 per cent. 



'See JoHT. Board of Agric'tllHre, xx, 1087 (1914). 



