34 Conditions affecting Growth 



The influence of the canopy on the quality of the timber is dealt 

 with, under Thinning, below. Too dense a shade will produce 

 tall, drawn-up trees lacking in diameter, of* a weakly nature, and 

 liable to fungoid and insect attacks ; on the other hand, if too thin, 

 the timber produced will be rough and knotty. 



The influence of the canopy upon the soil is seldom sufficiently 

 considered. A dense canopy kills off all surface vegetation, and the 

 leaf-fall, being protected from sun and wind, forms a layer of slowly 

 decomposing vegetable matter. The importance of this cannot be 

 over-estimated. Poor soils planted with shade-bearing trees are 

 improved in their fertility, so that at the final cutting the ground is 

 left in better condition than when first planted. 



In a wood of light-demanding trees only, the canopy is thin 

 and the leaf-fall is exposed to light and air, the layer of humus 

 is quickly decomposed, and moisture is not conserved. The 

 consequence is that the ground is covered with a surface vegetation 

 composed of grass and weeds. 



Thinning. It is necessary to plant the trees close together, in 

 the first place, in order that the lateral branches of the young trees 

 may be killed off by the shade afforded by the canopy, as early as 

 possible. The presence of a branch means the presence of a knot 

 (see Figs. 8 and 9) ; a dead branch forms a loose knot which will fall 

 out when the timber is sawn up into planks. 1 But as the young 

 trees grow, some of them must be removed in order to allow an 

 increased growing area for the remainder. 



The period at which thinning will be commenced will depend 

 upon a variety of circumstances ; the more important of these are 

 the distance apart at which the trees are planted, and the species of 

 tree. The closer the trees are planted, the sooner must thinning 

 commence. The first thinning must be done sooner in the case of a 

 light-demanding species than would be necessary, or even advisable, 

 in the case of a shade-bearing kind of tree. 



The first thinning will probably consist of dead or weakly 

 specimens ; also, there may be some undesirable species of tree 



1 This is an important consideration, and the neglect of it has gained a 

 bad reputation for our home-grown timber. 



