It is the chief goal of forestry to devise methods for felling trees that provide for the growth of a new forest crop and to ensure that adequate seed of desirable species is shed onto the ground and that conditions are optimal for seed germination and the survival of saplings. The basic rule of timber management is sustained yield; that is, to cut each year a volume of timber no greater than the volume of wood that grew during that year on standing trees.
Desirable timber species are usually those of the native climax vegetation (see ecology) that can perpetuate themselves by natural succession, although at times (intentionally or unintentionally) a forest may not represent the climax vegetation—such as the pine of the SE United States, which grows faster than, and has replaced, the hardwoods destroyed by fire and logging. The Douglas fir of Western forests is encouraged because it is more valuable than the climax vegetation of mixed conifers that tends to establish itself in the absence of human intervention. Planting trees of different sizes (either because of species or of age) prevents crowding and insures maximal growth for the given area. Extermination of diseases and insect pests is standard forestry practice.