. Bulletin (Pennsylvania Department of Forestry), no. 11. Forests and forestry. ii; 24 required but where natural regeneration is used one may find 20,000 or even 100,000 seedlings per acre. If we go into a mature forest stand and count the trees per acre we will find probably 150, or some- times 250, and occasionally 400; hence, we must conclude that a large proportion of the trees which start out cannot survive. Two ques- tions suggest themselves: What happens with the large number of trees which cannot mature? Why is it necessary to plant so many when only a small number can mature? If one
. Bulletin (Pennsylvania Department of Forestry), no. 11. Forests and forestry. ii; 24 required but where natural regeneration is used one may find 20,000 or even 100,000 seedlings per acre. If we go into a mature forest stand and count the trees per acre we will find probably 150, or some- times 250, and occasionally 400; hence, we must conclude that a large proportion of the trees which start out cannot survive. Two ques- tions suggest themselves: What happens with the large number of trees which cannot mature? Why is it necessary to plant so many when only a small number can mature? If one inspects a plantation of trees a few years after it was established he will be able to note a difference among the trees. Some are thrifty, which is shown by their rapid growth, others are average, while still others show no signs of growth whatever or may have died. If one returns ten years later this condition is still more pronounced. By this time they will have grown to such dimensions that their branches are beginning to interlace. A struggle has started between them. There is no longer sufficient space for all of them. They must battle with each other for light and food. Some will conquer and be known as domin- ant trees, while others will just about hold their own and be known as intermediate trees, while still others will be conquered and be known as suppressed or dead trees. This struggle for existence is found in all places where trees grow in the form of a forest, and re- sults in the elimination of the weaker specimens. At the same time it gives such drastic discipline to the dominant ones that they will produce a much higher grade of wood. Trees grown in dense stands are usually free from lateral branches for a consider- able distance from the ground and as a consequence the logs cut from them will be relatively free from knots; while trees grown in open stands or in open situations bear crowns which often reach almost to the ground and produce numerous knots. Such
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