Thinning

Thinning is a term used in agricultural sciences to mean the removal of some plants, or parts of plants, to make room for the growth of others. Selective removal of parts of a plant such as branches, buds, or roots is typically known as pruning.

In forestry, thinning is the selective removal of trees, primarily undertaken to improve the growth rate or health of the remaining trees. Overcrowded trees are under competitive stress from their neighbors. Thinning may be done to increase the resistance of the stand to environmental stress such as drought, insect infestation, extreme temperature, or wildfire.

This may be done to make the stand more profitable in an upcoming final felling or to achieve ecological goals such as increasing biodiversity or accelerating the development of desired structural attributes such as large diameter trees with long tree crowns.

Early thinning, say after 20 years rather than late thinning, say after 50 years has different effects on the trees thinned. An early thinning would encourage trees to get wider crowns, increase diameter and be more stable against threats like snow breakage or windthrow. Too much too early would lead to a site overgrowing with shrubs and prevent an understory regenerating effectively. Doing it too late would mean that trees would grow tall and slender and though some increment would come to the trees, they may be less marketable as thinness reduces value. Too early and epicormic shooting is a risk, and this can lead to tree branchiness and knots in the resultant timber harvest, again reducing value.

Traditionally thinning has been done to create a desired balance between individual tree attributes (such as tree diameter) and per area attributes such as volume. It has been, and often still is, applied with the desire to create uniform stands. Thinning treatments are often described in terms of number of trees per area to remain or average spacing between trees. The intent is to create and manage uniform stands. It is also more needed when too many trees were initially planted or survived from the seedling phase. Planting less and thinning less saves money in commercial forestry, so a good balance is required and is dependent on site qualities as well as planting régimes.

...
Wikipedia