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Mechanical stress generated by growing wood cells causes heart checks in the ends of timber, while lumber end-splits and warps. It is not possible to prevent these growth stresses but they can be minimized. Trees generate relatively high stress in order to bend stems and branches into positions more favorable for the tree, as is known from reaction wood, whose growth stresses are extremely high. One controls the stresses by giving trees no reason to reorient themselves, that is, by providing stable growth conditions. To this end, trees should have sufficient, uniform light, and where light is scarce, as in understories, one-sided light changes have to be avoided. In particular, the spatial distribution of trees in the stand should be uniform; multistoried forests are preferable to single-storied, even-aged plantations. The stands should be thinned slightly, frequently, and uniformly, rather than haphazardly and severely after long periods. In areas with strong prevailing wind, close spacing may minimize the stresses, whereas on steep slopes wide spacing appears to be preferable.

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