Use of English PRO

First, What is forestry? Forestry is the knowledge of the forest.
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For example, a forest may be handled so as to produce saw logs, telegraph poles, barrel hoops, firewood, tan bark, or turpentine. The main purpose of its treatment may be to prevent the washing of soil, to regulate the flow of streams, to support cattle or sheep, or it may be handled so as to supply a wide range and combination of uses. Forestry is the art of producing from the forest whatever it can yield for the service of man. Before we can understand forestry, certain facts about the forest itself must be kept in mind.
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It has a resident population of insects and higher animals entirely distinct from that outside. Most important of all, from the Forester's point of view, the members of the forest live in an exact and intricate system of competition and mutual assistance, of help or harm, which extends to all the inhabitants of this complicated city of trees. The trees in a forest are all helped by mutually protecting each other against high winds, and by producing a richer and moister soil than would be possible if the trees stood singly and apart. They compete among themselves by their roots for moisture in the soil, and for light and space by the growth of their crowns in height and breadth.
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The number of young trees which destroy each other in this fierce struggle for existence is prodigious, so that often a few score per acre are all that survive to middle or old age out of many tens of thousands of seedlings which entered the race of life on approximately even terms.
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Just as in New York City, for example, the French, the Germans, the Italians, the Hungarians, and the Chinese each have quarters of their own, and in those quarters live in accordance with habits which distinguish each race from all the others, so the different species of pines and hemlocks, oaks and maples prefer and are found in certain definite types of locality, and live in accordance with definite racial habits which are as general and unfailing as the racial characteristics which distinguish, for example, the Italians from the Germans, or the Swedes from the Chinese. The most important of these characteristics of race or species are those which are concerned with the relation of each to light, heat, and moisture.
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The tolerance of a tree for shade may vary greatly at different times of its life, but a white pine always requires more light than a hemlock, and a beech throughout its life will flourish with less sunshine or reflected light than, for example, an oak or a tulip tree.
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Thus a bald cypress will grow both in wetter and in dryer land than an oak; a red cedar will flourish from Florida to the Canadian line, while other species, like the Eastern larch, the Western mountain hemlock, or the big trees of California, are confined in their native localities within extremely narrow limits.