58 THE TREE AND ITS CHARACTERISTICS 



higher mountains and plateaus of Arizona and New Mexico. Spruce 

 which occurs at sea-level in the Northeast and eastern Canada is 

 found only on the highest elevations in the southern Appalachian 

 Mountains. 



The annular ring is generally separated into two distinct parts, 

 namely, springwood and summerwood. The former is light in weight 

 and coarse in texture compared with the darker, denser summerwood. 



Trees depend for growth upon: 



1. Moisture. Trees vary widely in their moisture requirements. 

 Water is necessary for the assimilation of food elements. Some trees 

 are water-loving or water-enduring, as cypress, willow, tupelo, water 

 hickories, and water oaks; others require dry or well-drained soils. 

 Hemlock and redwood thrive in moist, damp atmospheric conditions. 



2. Light is indispensable. It is said that trees literally convert 

 sunlight into wood. Light supplies the energy for the assimilation of 

 food. However, trees vary in their light requirements. Some trees 

 are tolerant of shade and will thrive under the canopy of other trees, 

 for example, spruce, beech, and hemlock. Others are known as intol- 

 erant, such as ponderosa pine, longleaf pine, and yellow poplar. Many 

 trees are intermediate as to tolerance. Site and moisture conditions 

 have an important bearing upon their tolerance. The difference in 

 tolerance is an important consideration in cultural thinnings, repro- 

 duction, and other phases of forest management. 



3. Temperature. A certain amount of heat is necessary for all 

 plant life. Trees cannot be transplanted successfully from warm to 

 cold climates, or vice versa. Each species has its optimum climate 

 and range of temperature in which it grows best. Exotic trees should 

 be grown in conditions similar to their native habitat. 



4. Soil. Soils have an important bearing upon tree growth. Trees 

 are usually stunted, crooked, and slow in growth in thin, rocky soils, 

 and conversely, thrive and exhibit the greatest health and vigor and 

 best form in good soils. Hardwoods require much better soils than 

 conifers. Soils and climatic conditions are usually unfavorable in the 

 higher mountains and therefore conifers are generally present. In the 

 rich agricultural sections, as in Ohio and Indiana, which have been 

 largely cleared for agricultural purposes, our finest and largest hard- 

 woods were found in the virgin forests. 



5. Oxygen. Oxygen is necessary for all forms of plant life. Vari- 

 ous chemical substances found in the air in addition to oxygen con- 

 tribute to the growth of tree life. 



