This, then, is the reason for modern forestry- the growing of trees for timber. where forest exist naturally, exploitation- the felling of all useful trees with no thought for the future- has been replaced by conservation- the felling of that volume of timber in year or a number of year as will naturally be replaced by growth in the same period. Nor is this felling haphazard; the trees are chosen not only for their size but also for their situation, so that younger trees are given space to develop, seedlings receive light enough to start their growth, and seeds find clear open spaces in which to fall and germinate. By this careful husbandry, called silviculture, the forest becomes self-perpetuating, producing a known quantify of timber each year, yet always covering and protecting the soil.