CHAPTER IV 

 HOW BIG TREES FROM TINY SEEDLINGS GROW 



JUST as a boy needs plenty of nourishing food, water, 

 pure air and rest for his development, forests like other 

 plant communities need certain factors for their proper 

 development. Air, light, and heat, and moisture and 

 plant food drawn from the soil are necessary for tree 

 growth. 



Air is a requisite since it contains the oxygen which 

 nearly all living organisms must have. Trees, like all 

 plants, breathe in oxygen and in addition to consuming 

 oxygen they also withdraw large amounts of carbon 

 dioxide from the air which is afterward combined in 

 the presence of the chlorophyll of the leaves with water 

 to make starch and sugar. 



Light, of course, is indispensable to growing trees. It 

 supplies the necessary energy for the assimilation of 

 food, and if light be removed the leaves soon lose their 

 green color and become incapable of manufacturing the 

 plant food, sugars and starches from carbon dioxide 

 and water. Different kinds of trees vary in their 

 light requirements. Some trees such as red cedar, gray 

 birch and most of the yellow pines of the South and 

 West need full sunlight for thrifty growth and are 

 called "intolerant" because they cannot endure shade. 

 Others, like hard maple, spruce, and hemlock, can en- 

 dure plenty of shade and are said to be "tolerant." A 

 tree can ordinarily live with less than the full amount 

 of light demanded by that species but to thrive and 



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