© 1966 by Institute of Chartered Foresters
Biological Aspects of Thinning in Conifer Plantations
Variations in the soil which affect the extent and health of tree root-systems occur on both a large and a small scale, and influence the crop during all the three principal periods of its life, i.e. during establishment, development, and decline. Their influence during the first period is responsible for much of the variation in the crop which is present when thinning begins in the second and vigorous growth is possible only so long as a proper balance is maintained between root-system and crown.
Variations in soil cause much of the variation in vigour and in the course of heightgrowth which can be found both between neighbouring stands and between neighbouring individuals within a stand.
Thinning must be adapted to these variations in soil-environment. On sites where the development period is short, early thinning is essential. On such sites it may be wise to adopt short rotations, or to plant species which are relatively insensitive to variation.
Areas of uniform site type, over which tree-growth follows a distinctive course, should form the units for management and silvicultural treatment. No single type of thinning régime should be applied everywhere; thinning should be closely adapted not only to economic requirements, but also to the pattern of growth and to site conditions.