Density of the Canopy 33 



Light- demanding and shade-bearing trees. In some trees, 

 the side branches are killed off by shading at an early 

 age, and, at the same time, the crown opens out. Consequently, 

 there is not sufficient shade on the soil ; so that grass and weeds 

 grow up, the accumulation of humus is lessened, and the grass 

 intercepts the rainfall and utilises the available water. Such trees 

 are termed " light-demanding " trees. Towards the end of a long 

 rotation of such trees, the annual increment — that is, the amount 

 of wood produced per acre per annum — is not maintained, owing to 

 the decrease of fertility in the soil. Such are oak, ash, larch. 



In other trees, there is a thick canopy which shades the soil, 

 so that grass and weeds cannot grow up, and humus accumulates. 

 Such trees are termed "shade-bearing," and in these, even towards 

 the end of the rotation, the annual increment is maintained, owing 

 to the upkeep of soil fertility. Such are beech and spruce. 



This difference between light-demanding and shade-bearing 

 trees must be considered in most questions of forestry, more 

 especially in relation to thinning and to mixed woods (see pp. 34 

 and 40). 



Canopy. The growth of the individual trees composing a wood 

 tends to cause the meeting and subsequent interlacing of the 

 branches. These interlacing branches form what is known as the 

 " canopy," and as complete a canopy as possible should be obtained 

 as soon as circumstances will permit. 



The density of the canopy will depend upon the capacity of the 

 species for bearing shade. If this quality is possessed, and a thick 

 shade over the tree-stems and soil is obtained, then the most 

 favourable conditions of growth are realised. 



A light-demanding species is unable to form a satisfactory 

 canopy ; for, at a comparatively early age, the crowns thin out, and 

 too much air and light are admitted to the surface of the ground. 

 These species, however, parting with their lateral branches more 

 freely, produce cleaner timber with less shade. 



It will be evident at once that upon the proper regulation of the 

 canopy depends the quantity and quality of the timber produced. 



