124 BRITISH FOREST TREES 



years of age. The increase in girth on the standards in 

 full enjoyment of sunshine and air is very rapid, and far 

 outweighs in technical and monetary value the loss of in- 

 crement on the young crop, without prejudicing the future 

 development of the latter in due time. Schuberg found a 

 greater cubic quantity of timber per acre on forests treated 

 thus than was to be found when the forests were reproduced . 

 more regularly in smaller blocks, where, with shorter periods 

 of reproduction, the trees forming the mature crops were 

 more nearly equal in age. 



Though the average rotation of silver fir is about 100 to 

 1 20 years in pure high forest, yet by reason of the special 

 treatment accorded to it for the production of boles girthing 

 well at the upper end, to suit the requirements of the 

 timber market, the actual fall is begun in the mature timber 

 about the eightieth to ninetieth year, and continued till final 

 clearance takes place often only as late as about the hundred 

 and thirtieth to the hundred and fortieth year. 



Mixed Forests with Silver Fir as the ruling Species. Among 

 conifers, spruce is of most importance as a subordinate 

 species in forests where silver fir forms the matrix or major 

 portion of the crop. Where it is intended that the spruce 

 is to remain permanently subordinate till the crop reaches 

 marketable maturity, care must be taken to protect the 

 silver fir whenever the thinnings take place, otherwise the 

 more rapidly growing spruce is apt to form canopy above 

 the silver fir, which then never afterwards gets a chance of 

 a fair share in the enjoyment of light and air. Where, how- 

 ever, the spruce has only been scattered individually through- 

 out young crops of silver fir, it develops into fine stems, often 

 of exceptionally good growth. For practical purposes in 

 Britain, the mixture of spruce with silver fir is of less import- 

 ance than that of silver fir with spruce (vide pages 99 to 101). 



As forests of silver fir are usually to be found only on 



