Approximately 150,000 acres of Tongass young growth (YG) is outside of the suitable and available timber base. These stands are not being managed for timber production, but are being managed for other ecosystem services such as wildlife habitat, riparian habitat, wildlife security areas, and for biodiversity. Not all of these non-timber stands will need treatment, but some will. Since timber production is not the objective of management, special treatments and prescriptions will be used to achieve the specific management goals.
The stands that will require treatments are the stands that have grown back as a dense stand of trees that are in, or about to enter the stem exclusion stage (crown closure). The primary objective of most restoration treatments is to create holes in this thick canopy. Openings are created by some type of thinning prescription. These openings allow light to reach the forest floor and stimulate the growth of other plants, such as shrubs and forbs and eventually a younger generation of trees. This creates biodiversity and can create wildlife habitat. The treated patchy stand begins to look and function more like the original old growth stand. It may take several treatments over many years to replicate the conditions of the original stand.
Some of these stands have been pre-commercially thinned (PCT), but most have not. PCT is an acceptable primary treatment as it maintains or reintroduces some light and resulting biodiversity into the stand. PCT is only a temporary short term treatment however, as its effects will only last about 15 – 25 years and then the stands will begin to close back in. PCT wind firms young stands, which helps alleviate future wind concerns. PCT also reduces some of the potential slash (cut trees) concerns from future treatments, by cutting most of the trees when they are small. This allows treatment option flexibility in the future.
Slash is a potential problem created by restoration treatments. These cut trees can pile up several feet thick when a stand is thinned. This thick slash impedes wildlife and human movement and slows the understory development. Thick slash can offset the treatment goals. Treating the slash itself is very expensive. Commercial thin (CT) treatments can reduce the slash load, utilizing the trees with value and selling or trading them (stewardship contracting – goods for services) to help offset the costs of the treatment. Leaving non-thinned areas within stands is an option to consider. These leave areas will have little slash and will contribute to biodiversity, provide travel corridors, serve as security areas, and provide snow intercept and thermal cover in the winter.
Thinning and restoring older YG (25+ years) presents more challenges than does thinning and restoring younger YG. The trees are larger and require more skill to cut, and when cut they create more slash. The older YG that has not been PCT will be more prone to blow down and snow loading when the stand is opened up. There are several types of terrestrial thinning prescriptions being tested and used to restore lost services and function in YG stands. These include:
- Variable density thinning, including various spacing between trees, thinning from above, thinning from below, and thinning to a basal area target.
- Gap thinning.
- Variable density thinning with skips and gaps.
In older YG stands with slash and/or wind and snow loading concerns, thinning by gap creation might be a good option. Gap treatments will concentrate slash to the area around the gap and minimize the area of the stand that is subject to wind and snow loading. Another consideration for slash concerns is to kill the trees by girdling the tree rather than falling the tree. That way the dead trees will gradually fall over and spread the slash on the ground out over time.
The Nature Conservancy has developed Restoration of Young Forests. This document that has suggestions, examples, and considerations from the Pacific Northwest, many of which are applicable to Southeast Alaska.