Crowns are the portion of the tree with live branches supporting needles or leaves.
The needles absorb sunlight, converting them to sugars for growth, in a process called photosynthesis . With species that require full sun, such as Dougas fir, thinning helps maintain fuller crowns. In selection harvesting , some trees are removed so species of seedlings that can tolerate shade will become established as part of the new forest. In contrast, thinning is not for the regeneration of new trees, but rather to remove some of the competition, giving the remaining trees more room to grow until harvest.