CORVALLIS - It increasingly appears that structure and characteristics similar to those found in old-growth stands can be successfully achieved in a managed forest, along with surprisingly high levels of timber production.
A recent study reviewed various research projects, along with findings from some particular activities in Oregon State University's McDonald Forest, and suggested that mature wildlife habitat can be significantly enhanced with minimum impacts on timber yield.
The study was published in the professional journal Weed Technology by Elizabeth Cole, a senior research assistant in the OSU Department of Forest Science.
"There would be some foregone timber yield and higher administrative costs, and more entries for tree thinning," Cole said. "But with a long-term commitment and more intensive forest management, the research indicates that diverse structure and timber production can be compatible."
One analysis done by an OSU scientist indicated that about 90 percent of the conventional timber yield could be achieved in a managed forest over a 70-year period. Meanwhile, the forest would bear a 90 percent similarity to a natural stand through repeated thinnings, replantings with different tree species, snag retention, and development of a multi-storied canopy.
Various forest treatments are under way now in McDonald Forest north of OSU's Corvallis campus to study the techniques that can produce such effects.
A particular goal of this research, Cole said, is to identify methods that could be used to create a more diverse forest structure in plantation forests in the Pacific Northwest, which are often an even-aged, Douglas-fir monoculture that are inadequate for some wildlife species.
The type of forest structure common to old-growth conifer forests, which biologists believe nurture a broader range of wildlife species, include large conifer trees, snags, coarse woody debris, some open gaps, and a complex understory structure.
The treatments to create similar characteristics, as outlined in this study, may include selective tree harvests; underplanting of shade tolerant species; some brush and weed control; snag creation through girdling, topping or even fungal injections into individual trees; and other techniques still being researched.
Creating the desired type of understory appears to be one of the more difficult challenges, Cole said, and studies now under way in McDonald Forest are trying to fine tune techniques to do that.
Another option for increasing structure complexity within a stand might be to leave clumps of maturing trees within conventional clearcuts, the study said. The size of the clump would vary based upon needs of wildlife species, susceptibility to windthrow, management objectives and other factors.
Economically, "it's clear that logging costs will be higher," Cole said, but there will be some costs offset by higher quality of products from the residual trees.
In one analysis of the cost of retaining stand structure, done in the Willamette National Forest, it was concluded that there was loss of from 0.2 to 8.5 per cent of the total merchantable timber volume.
Continued research will help clarify which techniques are most appropriate to achieve desired results, Cole said.