BRITISH FOREST TREES 219 



tree. They arc both capable of accommodating themselves 

 to soils of the most varied description, from dry sand to 

 marshy moors, and it often happens that naturally mixed 

 forests of these species are to be seen in fairly good growth 

 wherever the soil-moisture is supplied in sufficient quantity ; 

 where this condition is wanting, however, interruption of the 

 canopy and deterioration of the soil are too often the results. 

 Even on poor classes of soil, birch is more rapid in develop- 

 ment than pine until about the fifteenth to twentieth year, 

 but the latter then generally overtakes it, and succeeds in 

 suppressing it, unless it seems desirable to come to the 

 assistance of the birch when the woods are being tended by 

 thinning ; yet even then it is as a rule necessary to utilise it 

 about the thirtieth or fortieth year in order to avoid the bad 

 effects of a considerably interrupted canopy. On good, 

 moist soils birch can hold out a rotation of seventy or eighty 

 years along with pine, but its cultivation under such circum- 

 stances would be somewhat inconsistent with the fundamental 

 principle that in Britain sylvicultural operations must be 

 mainly guided by actuarial and financial considerations, as 

 the introduction of spruce, silver fir, or beech would yield 

 much better ultimate results in favour of the main crop of 

 pine. For fringing pine woods at every possible opportunity 

 however, there is no better species than birch, and even 

 this scant admixture can assert appreciable influence in 

 diminishing the dangers from insects, snow accumulations, 

 and fire. 



On the poorer qualities of beech soils, and in localities 

 where natural reproduction of the beech is a matter of diffi- 

 culty, birch and other softwoods usually manage to effect an 

 entrance and assert a foothold, often to the great detriment 

 of the former. Unless prompt measures be taken to secure 

 their removal, they maintain themselves so obstinately that 

 seedling growth of beech is a matter of impossibility. They 



