Notes and Research
Sustainable Timber Management
The forest landowner managing for forest health, restoration, fuels management, and non-timber forest products can often expect a limited flow of timber logs from the site, especially during initial treatments. Due to dry climate and poor site productivity, however, most forestlands in Montana are not suited for long-term, sustained-yield, commercial timber production. In those lands suitable to timber production, we urge that timber production accompany forest health and restoration objectives. Such mixed-objective approach would use various approaches to maintaining mature canopy structures while periodically removing some trees for timber value.
Some cover types, for example, are suited for uneven-age management, wherein two or three well-defined generations of trees are growing on the same stand. With uneven age management, foresters periodically remove trees using single-tree or group tree selection cutting, thereby realizing timber value and providing openings for new tree growth. We recommend leaving the oldest trees, with straight, defectless form, insofar as they are healthy, as they can provide good seed source as well as rich and sustainable non-timber value, especially in the context of the larger stand and forest.
Uneven-age management is more problematic in lodgepole forests, which have evolved to periodically burn in stand-replacing fires that kill all or most of the trees. Thus, lodgepole stands naturally grow in even-age structures. The seed source for new lodgepole stand regeneration is the bed of cones produced before the fire. Lodgepole cones are serotinous, meaning that they require heat (generally, from 105-155 degrees F.) to release the resin bond holding the cone scales together.
Under some circumstances, when treating lodgepole stands, we recommend applying large-group selection (1-3 acres), or variable-density thinning (VDT). The result is a mosaic-patterned uneven-age stand, though any given clump or group will retain an even-aged structure. Such an approach would be helpful when aesthetic objectives and fuel management objectives conflict. We then follow this VDT treatment with a sanitation thinning from below to remove ladder-fuels. A sanitation thinning involves removing saplings and standing dead pole-sized trees, being careful not to overthin, as lodgepoles are subject to windthrow. Such stands will allow regeneration of new generations and break up the fuel wall normally created by a lodge-pole stand, while creating some merchantable logs.
Treated lodgepole stands should be periodically monitored for windthrow, especially along the stand edges.
Uneven-age management is even less practical in drier climates, where frequent fires generally maintained even-age stands of mature trees, especially ponderosa pine and Douglas-fir. In limited cases, clumps of Douglas-fir can be encouraged and harvested when the tree has reached a merchantable volume, however this must be looked at as a long-term process (100 years and more in much of Montana).
O'Hara, Kevin L., Uneven-aged Management: Opportunities, Constraints, and Methodologies(Missoula, MT: Montana Forest and Conservation Experiment Station, 1995). Every essay in this book is worth reading.
Smith, David M., The Practice of Silviculture, 8th Edition(New York: John Wiley, 1986).