CLIMATE AND SOIL 29 



understood by British woodmen, and in a large number of 

 cases unsuitable species have been planted under the shade 

 of standing trees, with the result that the plantation has 

 failed. 



When considering whether any particular species, not men- 

 tioned in this list, is light-demanding or shade-bearing, a 

 useful broad rule is that a tree with a light thin crown is 

 usually a light-demander, while one with a dense crown is 

 a shade-bearer. 



7. The soil. The character of the soil is not so important 

 as that of the climate, nevertheless trees make certain demands 

 upon the soil which it must be capable of fulfilling; thus it 

 must give space for the roots to grow so that the tree may 

 obtain a good hold upon the ground, and it must give moisture 

 and nourishing substances in sufficient quantities. 



For practical purposes soils may be divided into clays which 

 contain over 60 per cent, of pure clay ; sands which contain 

 over 75 per cent, of pure sand ; loams formed of clay and 

 sand in fairly equal quantities ; limy or calcareous soils con- 

 taining over 10 per cent, of carbonate of lime ; and peats 

 which consist chiefly of vegetable matter with very little 

 mineral earth. These soils merge one into another and thus 

 we get such soils as loamy sands, sandy loams, loamy clays, 

 loamy limes, &c. Marls are limy soils with over 30 per cent, 

 of clay, the lime being equally admixed throughout each 

 particle of soil. 



With regard to the mineral composition of a soil, the minerals 

 most necessary for the growth of forest trees are potash, lime, 

 magnesia, iron, sulphur, and phosphorus, and fortunately 

 almost every soil contains these minerals in sufficient quantity 

 to support tree growth, though possibly there may not be 

 enough water to hold them in solution, in which condition 

 alone can they be absorbed by the roots. A crop of trees, 

 provided the humus or layer of leaf-mould formed by the 

 decaying leaves is not removed, requires a far smaller quantity 



