216 BRITISH FOREST TREES 



unite the qualities necessary to improve in the slightest 

 degree, or even to conserve against deterioration, the pro- 

 ductive capacity of the soil. Except during the earliest 

 periods of growth, when all forest trees protect the soil, the 

 ground is only too apt to become overgrown with grasses 

 and rank growth of weeds on moister localities, or with 

 whortleberry and heather on drier situations. Where the 

 birch occurs more frequently than simply scattered here 

 and there, it is not usually considered a very creditable 

 sign of able sylvicultural treatment. With its light seed, it 

 is apt to make its appearance in large numbers wherever 

 clearances are made in the vicinity of seed-bearing trees, 

 and often becomes a perfect weed, the eradication of which 

 not infrequently causes great trouble. Wherever it has 

 been retained as a ruling species under such circumstances, 

 or wherever it has been deliberately sown with the intention 

 of yielding early and good returns as a quick-growing 

 species, deterioration of soil has in general been the result, 

 for the insufficient overshadowing of the ground, and the 

 light fall of foliage render it incapable of forming much mould. 

 Even on soils by no means deficient in humus, the birch is of 

 itself unable, when in large groups, to protect the soil from 

 deterioration for any length of time. Where such experi- 

 ments have been made, although the first crop of birch 

 may have been satisfactory, later crops (especially when 

 formed from stool-shoots) have only too often necessitated 

 the planting up of areas with Scots pine or spruce, in order 

 to revive the deteriorated productive capacity of the soil. 

 To a certain extent this failure is due to relying too much 

 on the natural capacity for reproduction through root- stools, 

 in place of carefully selecting plants of seedling growth for 

 the second and following generations, as though the develop- 

 ment of the stool-shoots is lively and energetic at first, they 

 do not remain faithful to this early promise, but soon fall 



