THE LIFE HISTORY OF TREES IN THE WOODLOT 41 



continues with even greater severity than before. Each tree 

 now strives to spread more and more of its crown to the light 

 and many trees are crowded out and die. 



(d) The Period of Declining Vigor in the Trees. — This 

 last period is the mature stage in the life of the trees. Height 

 growth has practically ceased and the trunks are increasing in 

 diameter slowly. The sidewise competition of the crowns will 

 have nearly stopped and the number of trees in the final stand 

 will practically have been reached. As the crowns flatten out 

 they become thinner and allow more and more sunlight to 

 pass through to the forest floor. Grass, weeds and berry 

 bushes begin to come in. Seedlings which are able to endure 

 more shade than the older trees spring up beneath the trees. 

 These little trees are the children of the forest. It is on them 

 that the future life of the woodlot depends. When the old 

 parent trees die and fall to the ground or are harvested, these 

 young seedlings, which have been nourished and protected be- 

 neath their crowns, spring up and take their places, filling in 

 the spaces left in the canopy. 



The trees are ripe for the harvest. If allowed to live longer 

 they will become attacked by insects and decay and be broken 

 by storms. As long as trees are growing vigorously in youth 

 they are usually able to withstand the attacks of enemies. 

 Because of the rapid diameter growth wounds are closed over 

 quickly and insects are not able to gain entrance. But with 

 the slower growth in old age, wounds remain exposed a long 

 time to the air. Fungi which cause rot in the wood gain en- 

 trance and the tree begins to decay. Owing to the weakened 

 condition insects attack the trees and burrow deep into the 

 wood. Storms break off the older branches which have become 

 brittle with age. Many trees that have become weakened by 

 disease are broken off or uprooted by the wind. Younger trees 

 grow up to occupy the place of those that have fallen. Soon 

 all the old trees will be gone, and a new forest, composed of 

 younger trees, will take possession of the soil. 



