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Years Of Growth: Lateral growth in trees frequently begins later than growth in height, but the period of lateral growth is longer. Rates of lateral growth likewise are low at the outset, increasing after a few weeks and then diminishing. In view of the long annual period of lateral growth in trees, deleterious environmental conditions may exercise a pronounced effect on growth. In the wood of trees of temperate regions, narrow and wide growth rings may be observed, marking years of growth characterized by unfavorable and favorable conditions for growth.
The problem of human growth—the population explosion—must be understood in the same context as the growth of populations of other organisms. At present the human population is in a growth phase with a mean doubling time of about 25 years of growth. Although the number of humans an double every 25 years of growth, the food supply cannot Jo so indefinitely.
Annual Growth.—An individual tree located in a favorable situation grows relatively slowly as a seedling, and rather faster as a sapling and young tree. However, upon reaching maturity, the rate of annual growth decreases to a low level. This pattern of behavior is well illustrated in the decreasing width of the annual growth rings of mature and old trees. There is relative uniformity in the over-all patterns of growth of various tree species, although the actual patterns may differ widely in individual trees of different species. For example, individual Sitka spruce trees in the Pacific Northwest may continue to grow rapidly in height and diameter at 150 years of growth of age, whereas red spruce trees in northeastern North America have reached maturity in less than 100 years of growth, and will grow a negligible amount in subsequent years of growth.
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