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 hke 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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