RISKS 2il 



mature and over-mature timber, and is a serious factor in opera- 

 tions where a portion of the stand is left for a second crop or as 

 seed trees. If all parts of a tract are accessible, wind-thrown 

 timber can be marketed without loss, provided the quantity 

 thrown does not exceed the capacity of the operation as gauged 

 by the length of time the down trees can be left without deterior- 

 ation. 



202. Insects. Imported insects as, for example, the gypsy 

 and brown-tail moths are far more dangerous to forests than 

 native insects, as they are practically without any natural 

 parasites. The introduction of these enemies now promises to 

 keep the gypsy moth in check. 



Native insects occasionally develop possibilities of injury, 

 and may destroy great areas of forest. They are finally checked 

 by disease or parasites. The worst of these insects are the bark- 

 boring beetles. Defoliating insects, like the larch sawfly or 

 spruce bud worm, may kill timber over entire regions. The 

 destruction of native birds explains the increase of certain 

 forms of injurious insects. Woodpeckers are very useful in 

 keeping boring larvae under control. 



203. Fungous Diseases. The only conspicuous instance of 

 widespread destruction of an American species due to fungous 

 attacks is found in the ravages of the imported disease of the 

 chestnut, Diaporthe parasitica, which threatens to exterminate 

 what is considered the most important commercial hardwood 

 over wide regions east of the Appalachians. Great damage is 

 done to the heartwood of all species of trees by fungi which 

 gain entrance through wounds or knots. These fungi do not 

 kill the trees as they have no effect on the living tissue. This 

 damage is greatest in old timber and is not a serious factor in 

 second growth. 



204. Climatic Injuries. Excessive drought in rare instances 

 kills many trees of the more susceptible species in exposed 

 regions or localities. Trees unused to swampy conditions are 

 killed by prolonged flooding of the roots. 



Minor injuries are caused by breakage in sleet storms or heavy 

 snows, permitting fungi to enter. Reproduction is especially 



