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As seedlings grow bigger, they begin to compete with one another for the resources they need to survive, resulting in some seedlings and young trees dying-off.
In many Pacific Northwest forests, previous managers have removed the very features that gave the forests their structural complexity—such as big trees, large snags, down logs, and multi-layered canopy—and then planted seedlings at dense spacing. These crowded, overstocked stands often have diminished tree growth, poor wildlife habitat, low understory diversity, and increased wildfire risk. In planted stands that have been artificially overstocked, there’s often a need to do some thinning.
Thinning helps the remaining trees better access the water, soil nutrients, and light they need to grow vigorously and resist insects and diseases. It also helps release the space and light needed to activate understory vegetation growth and thereby improve habitat and food available for wildlife―increasing overall biodiversity. Thinning can also be a tool to reduce wildfire risk in the “dry-side” ecosystems common in central and eastern Oregon and Washington.
Young-stand thinning (aka pre-commercial thinning) is a silvicultural practice that entails removing the individual trees that are declining―often they are smaller and have less robust crowns―and are less than 20 years old.
While young-stand thinning is sometimes done at a cost, the resulting long-term forest health benefits can improve the returns for commercial harvests in the future. “To delay the thinning and wait for the trees to grow enough to make the thinning harvest profitable is appealing, but deceptive. It may avoid the short-term expense, but is likely to weaken the stand at a long-term cost of growth, stand stability and future options,” says OSU Forestry & Natural Resource Extension Agent Brad Withrow-Robinson in the Tree Topics blog.
Additional resources on thinning and other topics are available in the NNRG Resource Library.