38 FARM FORESTRY 



able to grow faster than others, because their roots are better 

 developed, and so can secure more food and moisture from 

 the soil, or because they have found a better soil than the 

 trees about them, or because they are naturally hardier and 

 stronger trees than their neighbors, and so are able to grow 

 faster. As the trees become larger the demand for light and 

 space increases. It is not long before the trees begin to crowd 

 each other. Not only do they contend above for space and 

 light, but below the ground a struggle is going on between 

 the roots for food and moisture. Whenever a branch becomes 

 overtopped by a branch from a neighboring tree it is weakened 

 from loss of sunlight. The leaves on it are not able to manu- 

 facture as much food as before and do not transpire as much 

 water. Less and less amount of mineral food from the roots 

 is carried to them and a correspondingly greater amount is 

 carried to the healthy leaves above. The growth of the branch 

 gradually becomes slower, the leaves wither, and finally the 

 branch dies. Only those branches on which the leaves are 

 exposed to the light and are able to manufacture food can 

 live, and as fast as these become overtopped they will also die. 



Tree Crown Classes. — As the trees continue to grow those 

 that make the fastest height growth soon outstrip their neigh- 

 bors. Not only have they ample room to send their tops up into 

 the air, but their crowns being above those of their neighbors 

 are able to spread out sidewise. They become the most vigor- 

 ous trees in the stand and are called the dominant trees. The 

 trees that have been overtopped by the crowns of their faster 

 growing neighbors fall behind, and their growth becomes very 

 slow because of lack of light. These are the overtopped or 

 suppressed trees. Those trees that are being crowded by their 

 more vigorous neighbors, but still have a portion of their 

 crown to the light, are called intermediate or codominant 

 trees. 



The Struggle for Existence.— The struggle that started 

 with the coming together of the crowns soon becomes very 



