48 THE BOOK OF FORESTRY 



soon die from lack of light and food and the next high 

 wind or ice storm breaks them off leaving the lower part 

 of the trunk bare of limbs. This process is called 

 "natural pruning" and explains why trees which grew 

 in dense stands in their youth produce such splendid 

 clear timber free from knots. Whenever a tree is found 

 with thick, wide-spreading branches low down on 

 the trunk it is certain that this individual had full 

 light upon all sides when it was a sapling else it would 

 not have kept these limbs so long. 



During this period of rapid height growth every tree 

 is struggling for all the sunlight it can get. Each 

 acre of ground has just so much rain and so many 

 days of sunlight in the growing season. Naturally if 

 the seedlings have been very densely sown by Mother 

 Nature, say 10,000 or 15,000 per acre, there is not 

 enough food to go around and those that were weak 

 or a little slow in getting started fall behind. Once 

 they are overtopped, sunlight is cut off which deprives 

 the submerged tree of the energy required to assimilate 

 its food and then it dies of starvation, or soon falls a 

 prey to fungus or insect attacks. 



In this way the number of pine or spruce trees 

 standing upon an acre of the old pasture becomes 

 greatly diminished during the first forty years of reoc- 

 cupation. By that time the weakest have fallen down, 

 have rotted and may have vanished completely beneath 

 the needle carpet. The leaves and twigs which have 

 fallen as well as the trunks, have decomposed to form 

 the layer of dark mold or humus lying on top of the 

 mineral soil while on top of the humus may be found 

 the carpet of needles and twigs which have not yet 

 been long enough exposed to fungi and bacteria to have 

 lost their structure. 



