26 MISC. PUBLICATIOX 16 2, U. S. DEPT. OF AGRICULTURE 



gradually grows down through it, eventually causing the death of 

 the tree. As yet no practicable means of controlling the chestnut 

 bark disease lias been found but tliere is evidence that sprouts and 

 other young chestnuts are developing resistanee to the disease. 



Another fungous disease is the white pine blister rust which, 

 strange as it may seem, lives alternately on the pine and on currant 

 and gooseberry plants. The disease enters the white pines through 

 the needles and grows into the bark. Diseased áreas in the bark 

 are called cankers. About 3 years after a tree becomes infected 

 orange-yellow blisters break from the cankers. In the spring mil- 

 lions of spores from these blisters are scattered by the wind over 

 long distaiices, infecting the leaves of currant and gooseberry bushea 

 The disease caimot go directly from one pine to another, but must 

 first go to currants or gooseberries. It is the spores produced on the 

 leaves of these plants that are dangerous to the pine trees. Since 

 these spores are delicate and short lived their infecting range is 

 limited to relatively short distances. Thus it is possible to control the 

 disease locally by destroying currants and gooseberries in the vicinity 

 of white pines. 



Other Enemies 



Animáis grazing in the woods can do serious dainage to both the 

 mature trees and the young growth. The older trees may be injured 

 by having their roots trampled and wounded and by having the soil 

 around them compacted to such an extent that it is nearly impervious 

 to water. Young growth is often entirely destroyed. Cattle, horses, 

 sheep, and goats browse young seedlings, particularly the hardwoods, 

 trample them down, or brush against them and break them. Hogs 

 eat the seed of certain trees and thus prevent new growth from start- 

 ing. They actually root pine seedlings out of the ground and eat 

 the fleshy covering of the roots. Grazing in woodlands should there- 

 fore be carefully regulated if the stand is to reinain productive. 



In localities where trees are shallow rootecl, or the ground is soft 

 because it is soaked with water, or where the trees have been weak- 

 ened by fire or other agencies, windstorms can cause extensive dam- 

 age. A bad blow down may become a fire nienace, as well as a waste 

 of valuable timber. 



Snow may also be very harmful, especially to young trees. It 

 often loads them down, breaks, or deforms them, especially if wet 

 snow falls heavily before the broadleaf trees have shed their foliage 

 in the fall. In many regions, however, snow is so useful in protect- 

 ing the soil and the young trees that the harm it does is offset by its 

 benefits. 



FORESTRY IN THE UNITED STATES 



What Forestry Is 



Forestry is the handling of forest land in such a way that it will 

 raise repeated crops of timber and will exert to the fullest the bene- 

 ficial influences of the healthy forest on soil and stream flow, on wild- 

 life and human life. Lands that can best produce forest crops 

 should be kept at work growing trees. 



