WHAT FORESTRY IS AND WHAT IT DOES 183 



aid. Different trees have different requirements with 

 regard to water, food and Hght. Some need more water 

 and food than others, some will not endure much shade, 

 and others will grow in the deepest shade. In the open, 

 a tree, if once established, can meet its needs quite readily 



i>r> tic-* 



Fig. 124. — Measuring the Diameter of a Tree and Counting 

 its Annual Rings. 



and, though it has to ward off a number of enemies, 

 insects, disease and windstorm — its struggle for existence 

 is comparatively easy. In the forest, the conditions are 

 different. Here, the tree-enemies have to be battled 

 with, just as in the open, and in addition, instead of there 

 being only a few trees on a plot of ground, there are thousands 



