CHARACTERISTICS OF TREE GROWTH 



55 



other plant foods. This process of tree growth is known as assimila- 

 tion. If the foliage is removed or light is not provided, the tree will 

 weaken and gradually die. The flow of sap in trees is not entirely 

 understood. In general, the sapwood conducts the water from the 

 roots to the leaves where the assimilation process goes on and much 

 of the water is evaporated in the air. Some acres of forests may take 

 annually from the soil and give 

 up to the leaves from 500,000 

 to 1,500,000 pounds of water. 

 Leaves of deciduous trees tran- 

 spire one-sixth to one-third as 

 much water as an equal surface 

 of water. Coniferous trees tran- 

 spire less than one-sixth as 

 much as deciduous trees. (For 

 further explanation, see any 

 good textbook on botany.) 



*A~*^" 



The falling leaves in the au- 

 tumn furnish nourishment to the 

 soil and consistently build up 

 and maintain its fertility. , There- 

 fore, leaves should not be burned 

 in surface fires. Some trees, 

 such as black walnut, yellow 

 poplar, hard maple, and bass- 

 wood, require the finest type 



of fertile soils to attain the best development. Beech is known as the 

 mother of the forest in Europe, as it furnishes leaves which add much 

 to the fertility of the soil. .^ 



FIG. 29. Douglas Fir (Pseudotsuga taxi- 

 folia) bark, leaves, and cones. 



3. CHARACTERISTICS OF TREE GROWTH 



Trees may be classified as to crown dominance, or the position of 

 the crown in the canopy of a forest, as follows: 



1. Dominant the tallest and largest crowns in the canopy. 



2. Co-dominant those slightly below the dominant crowns. 



3. Intermediate those occupying a middle position in the crown 



canopy. 



4. Overtopped those which have been surpassed in the struggle 



to reach the upper part of the canopy and have been crowded 

 out. 



