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The preceding discussion has been concerned primarily with the occurrence of regeneration originating from seeds after harvest of all or part of the overstory. However, in many forest types, particularly those with shade tolerant species, seedlings in situ at the time of timber harvest, "Advance Growth," may be a more reliable source of future stands than post-harvest germinants.

The following 7 pages are taken from: McCaughey, W.W. & Ferguson, D.E. 1988. Response of Advance Regeneration to Release in the Inland Mountain West: A Summary. USDA Forest Service General Technical Report No. INT 243. Factors to be Considered

Today's decisions on silvicultural prescriptions will affect forest stands for many years. Tree, stand and site factors must be taken into consideration to determine the best management strategy for a stand. Several factors complicate the decision of whether to retain advance regeneration. First is our imperfect knowledge of response to release. Second is differences in objectives of landowners. While one owner may be willing to leave advance regeneration, another owner may not. Third, even within an ownership prescriptions will vary. One site might be good for releasing advance regeneration; another site might produce better yields if given a different prescription.

Featuring advance regeneration in the next rotation may or may not be the proper silvicultural prescription.

Advantages

There are several advantages in saving advance regeneration. Trees that respond to release with increased height and diameter growth provide immediate stocking and, because of their initial size, reduce rotation length. Site preparation and planting costs are reduced. Often, advance regeneration either stocks sites that are difficult to regenerate or provides shade for subsequent natural regeneration. Maintaining a continuous "green" forest helps provide hiding cover for wildlife and improves the esthetic appearance of a stand. Soil erosion is also reduced.

Disadvantages

There are also disadvantages to saving advance regeneration that should be considered. By featuring advance regeneration, stand succession is accelerated toward climax, increasing susceptibility to insect and disease problems. Advance trees are typically shade-tolerant species, and most are host to the Douglas-fir tussock moth and the western spruce budworm. Stem and root rots are common in older suppressed trees or in logging-damaged trees. Logging damage is often hard to prevent. Another disadvantage of saving advance trees is that disgenic practices may be encouraged. Advance trees are often saved even though they may never produce a commercial product. Contracts requiring protection of large amounts of advance regeneration may increase logging costs.

When It Should Be Used

For timber objectives, advance regeneration should be relied on only where growth after release is adequate and there is little risk of trees harboring future problems such as defect and decay. Advanced regeneration that does not respond well to release or takes too long to adjust should not be counted in regeneration surveys. Such trees do not meet the intent of the National Forest Management Act of 1976 or state forestry practices acts because projected yields will not be met. Alexander recommended accepting advance regeneration when it has good form, is able to make vigorous growth when released, and is free of defect or mechanical injury, no matter what its size. Ferguson has developed guidelines for defining acceptable advance regeneration.

Recommendations

If releasing advance regeneration for future crop trees is the management objective, avoid logging damage to advance trees, favor the most vigorous trees, and wait 2 to 5 years before evaluating release response.

Avoiding logging damage to advance regeneration decreases the number of passageways for diseases such as Stereum saguinolentum, Phellinus pini, and Armillaria mellea. Logging activities can also cause deformed boles, root wrenching, and soil compaction. Gravelle discussed ways to reduce logging damage to advance regeneration.

Trees growing the best prior to release generally have the highest post-release growth rates. Trees having live crown ratios greater than 50 percent respond with greater height and diameter growth than trees with low crown ratios. It is important to examine foliage color and density when evaluating the potential of advance regeneration.

Wait 2 to 5 years after logging before evaluating release response of advance regeneration. Nearly all 11 species responded to release in the 2- to 5-year period after release. Advance trees must adapt to increased levels of light. Release response is highly variable, not only between species but also within a species on a specific site. For example, McCaughey found that Engelmann spruce of the same age did not have similar post-release height growth and some spruce did not respond, while others increased annual height growth by nearly five times pre-release growth rates. Advance regeneration is often found in dense clumps. After waiting 2 to 5 years, slow-growing trees can be thinned from the clump to further release and evenly space the more vigorous trees. Growth rates of released trees should be compared to growth of planted or natural subsequent trees. Seidel provided methods for such a comparison.

The following material discusses factors to be considered when evaluating the role of advanced regeneration of several northwest species in planning for natural regeneration.

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