130 FARM FORESTRY 



cutting from the woodlot the trees on which the particular 

 insect feeds and encouraging the more resistant kinds. In 

 starting a woodlot by planting only those trees should be used 

 that are not subject to insect attacks. It is impossible to grow 

 the black locust in many parts of its range because of the 

 attacks of the locust borer that riddles the wood of the trees. 

 It is said that this insect lives on the pollen of the goldenrod 

 and that where this is destroyed locust trees can be grown. 

 There is no practical method of combating many kinds of 

 insects. 



Fire. — Fire is one of the worst enemies of the woodlot. 

 It not only injures large trees but it destroys the young trees 

 and seedlings on which the future of the woodlot depends, 

 and also destroys the favorable conditions of the forest floor 

 and soil. It is often thought that a surface fire passing through 

 a woodlot consuming the fallen leaves does scarcely any dam- 

 age to the larger trees. This is because the crowns of the 

 trees are elevated high above the fire and the bark on old 

 trees is usually thick. A surface fire may be hot enough to 

 scorch and kill the living cambium layer lying just beneath 

 the bark without the tree showing scarcely any outward evi- 

 dence of injury. The damage done to trees after a fire often 

 does not become evident for many years. When the cambium 

 layer is killed by being scorched, growth will cease over that 

 portion of the trunk of the tree and decay of the wood will 

 soon set in. The cause of so many large trees being rotten at 

 the base is usually surface fires that have killed the cambium 

 layer. Fungi gaining entrance through the dead bark spread 

 out in the wood often rotting the heartwood for long dis- 

 tances. When such trees are cut they .must be butted off 

 many feet to get above the decay. On level land trees are 

 injured most from a surface fire on the leeward side or the 

 side away from the direction from which the fire comes. 

 The direction in which a fire burned and usually the place 

 where the fire started can often be determined by this means. 



