Thinning is the removal of trees to achieve a desired spacing and number of remaining stems per acre. It is most commonly used in plantation forestry to prevent overcrowding and promote the health and growing speed of the remaining trees. After the trees are removed, the remaining trees have more space to grow, more soil nutrients, and more water per tree.

Trees that are removed are typically slower-growing, diseased, or poorly formed trees leaving the most vigorous, dominant trees to grow. It is a common forest management practice and the merchantable stems harvested are used to make fuel chips or pulp chips. Earlier thinning in younger non-merchantable stems is becoming a common practice. Stems cut in pre-commercial thinning are left in place to decompose.

It is a common practice used in agriculture as well as forest management.