Thinned areas of forest showed nearly 26% greater growth than unthinned areas.
"scientists found that in the thinned areas, average growth was nearly 26 percent greater than in the unthinned areas, when adjusted for species, initial tree size, and crown class. Midstory trees and the understory also responded positively. The stand conditions prior to the most recent thinning influenced the magnitude of the growth. “Tree growth was greatest if the stand had not been previously thinned,” notes Harrington. This article goes into why variable density thinning, leaving a gap "here", thinning moderately "there", and leaving clumps of trees enables a healthier forest. In fact this article shows that "Tree growth in all stands (including those 60-80 years old) increased in response to thinning in a fairly short period."