THE PRINCIPLES OF FORESTRY 



167 



be cultivated for a much longer period than where they are 

 only four feet apart. 



Mixed plantings are made by setting alternate rows of 

 two or three varieties. There are a number of advantages 

 derived from the mixing of the trees instead of planting only 

 one kind (Fig. 92) : 



Fig. 92. — A shelter-belt of mixed hard woods. This form of fence will protect the 

 forest from grazing stock. (Plant Industry.) 



1. There is less danger of total loss from drought, insects, 

 and diseases. 



2. Rapid-growing trees may temporarily fill the area 

 while the slower and more permanent ones are becoming 

 large enough. 



