70 THE SCHOOL BOOK OF FORESTRY 



always present in the forest. However, it is only 

 occasionally that they concentrate and work great 

 injury and damage in any one section. At rare 

 intervals, some very destructive insects may 

 centre their work in one district. They will 

 kill a large number of trees in a short time. 

 They continue their destruction until some 

 natural agency puts them to flight. The fungi, 

 on the other hand, develop slowly and work over 

 long periods. Sudden outbreaks of fungous 

 diseases are unusual. 



Heavy snows, lightning and wind storms also 

 lay low many of the tree giants of the forest. 

 Heavy falls of snow may weigh down the young, 

 tall trees to such an extent that they break. 

 Lightning it is worst in the hills and mountains 

 of the western states may strike and damage 

 a number of trees in the same vicinity. If these 

 trees are not killed outright, they are usually 

 damaged so badly that forest insects and fungi 

 complete their destruction. 



Big trees are sometimes uprooted during 

 forest storms so that they fall on younger trees 

 and cripple and deform them. Winds benefit 

 the forests in that they blow down old trees that 

 are no longer of much use and provide space for 



