Forest Products Laboratory Research Program On Small Diameter Material

Forests in the United States contain a significant amount of small-diameter and underutilized material. These overstocked stands not only increase the risk of insect, disease, fire, and drought damage, but also are costly to remove. Finding economical and marketable uses for small-diameter and underutilized material would alleviate these problems while improving watershed health and providing economic opportunities for local communities to help offset forest management costs. An extensive research program at the Forest Products Laboratory of the USDA Forest Service is focused on searching for economical and marketable uses for small-diameter material. The projects described in this report range from conserving timber through improving sawing technology to developing businesses for using small-diameter material.

Log moisture content has an important impact on many aspects of log home construction, including log processing, transportation costs, and dimensional stability in use. Air-drying times for house logs from freshly harvested trees can depend on numerous factors including initial moisture content, log diameter, bark condition, and environmental conditions during drying. In this study, we evaluated air-drying properties of young-growth Sitka spruce (Picea sitchensis (Bong.) Carr) and of western hemlock (Tsuga heterophylla (Raf.) Sarg.) from logs harvested in southeast Alaska. For each species, we considered inside storage in a warehouse vs. outside storage, as well as debarked logs vs. logs with bark remaining, resulting in four experimental treatments. We considered moisture losses after 8 and 12 months of air drying. There was considerable moisture loss for Sitka spruce logs, and much of the drying occurred during the first 8 months. Fastest drying rates for both species were for peeled logs with inside storage. Western hemlock logs showed higher moisture content and greater moisture content variation (vs. Sitka spruce), and in most cases would require additional drying beyond the 12-month study period to produce satisfactory house logs. Results of this study are significant because they can help entrepreneurs determine appropriate levels of capital investment (e.g., land, covered storage, debarking equipment), as well as whether to dry and process logs in southeast Alaska vs. some other location. This study found that a leading option for local producers would be to peel Sitka spruce logs, then air dry indoors for between 8 and 12 months. Another effective strategy would be to peel western hemlock logs, then air dry indoors for 12 months.