This, then, is the reason for modern forestry-- the growing of trees for timber. where forests exist naturally, exploitation-the felling of a useful trees with no thought for the future --has been replaced by conservation-- the felling of that volume of timber in a year or a number of years as will naturally be replaced by growth in the same period . Nor is this felling haphazard; the 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 quantity of timber each year, yet always covering and protecting the soil.