A thinning is just that— if a stand of trees has "too many" trees, then one thing we can do is cut some trees out, or "thin" the stand, so the remaining trees can grow better... faster... and stronger! One or more thinnings are often conducted before the stand reaches maturity.

Thinning is often necessary because the working forest begins as a large number of small trees. A planted stand in western Oregon can have several hundred trees per acre, while a seeded stand may have thousands of small trees per acre! As trees in a stand grow larger, they need more space. If we don't provide trees with space, then natural thinning will occur where some trees will beat other trees for limited resources like sun and water, and the losing trees will die.

The difference between a thinning and a partial cut reproduction method is that trees are cut in a thinned stand to benefit the remaining trees, whereas trees are cut in a partial cut to vacate enough space for seedlings to be able to grow and regenerate the forest.