There is a long history of the mechanical thinning of forests in standard forestry operations. Thinning typically involves removing some 30–50% of the standing volume of trees with commercially valued logs removed via tracked or wheeled machinery. More recently, thinning has been proposed to limit wildfire, drought, insect outbreaks, and increase water yields in many forests around the world. But is thinning in this regard effective and what are the associated costs and benefits?