Page:Timber and Timber Trees, Native and Foreign.djvu/43

III.] Trees grown in a copse might be expected to unite the leading characteristics of the two forms of growth just mentioned, inasmuch as, while the underwood remained, the upward tendency of the stem would be almost as strong as in a forest-grown tree, while each time the copse was cut, the branches would have perfect freedom of growth. It is, however, found that, although forming curved branches and a greater length of stem than can be met with in isolated trees, instead of the wood being uniformly harder, the changes of temperature to which the trees are subjected by the periodical loss of the protecting underwood renders the quality of such timber extremely variable.

Variety of soil also exercises a direct influence upon the quality of timber; trees grown in a dry, rocky soil having generally hard, compact wood; while the wood of those grown in swampy and moist situations will be found comparatively soft and spongy in texture. Variations of temperature, violent storms, or proximity to the sea or large rivers, will also affect the quality and rate of growth of trees.

It has long been supposed that the presence of trees tends directly to keep up the water supply, and that the clearing of large forests results, in time, in the drying up of all the springs and watercourses in the neighbourhood. That such an effect is produced is certain, as attention was lately drawn to it by the condition of large tracts of land in the South of France and other districts, which, though long celebrated for their fertility, were rapidly becoming valueless. The change in the nature of the soil, consequent upon the partial drying up of all the sources of water supply, was proved to have commenced when the trees had been removed. At the same time, it is said that in places where there