By Matt Aro, Wood Utilization Scientist, Natural Resources Research Institute, University of Minnesota—Duluth); co-contributor Kristen Bergstrand, Utilization and Marketing Coordinator, Division of Forestry, DNR
Minnesota's balsam fir forests may be the future source of outdoor furniture or high-performance fiberboard. Even better, balsam fir can be thermally treated to reduce rot, offering a more environmentally friendly alternative to using wood treated with damaging chemicals and shipped in from other states. Balsam fir's industrial use is similar to that of spruce. It is used primarily for making high quality paper. Sawmills can use it to make studs and orientated strand board.
Today, the opportunity to harvest Minnesota balsam fir is ripe. Since the 2008 recession, Minnesota's balsam forests have been aging and rotting much faster than they've been harvested¹. Annual state harvest of balsam fir in 2005 was almost 200,000 cords. However, it has declined ever since, with only 101,900 cords harvested in 2013 (a 50 percent decrease from 2005). Tamarack has also experienced a 40 percent decrease in harvest from its peak in 2010. Also, some of Minnesota's over-aged forests are falling prey to pests such as larch beetles (tamarack) and spruce budworm (balsam fir), and losing merchantability and fiber quality. Aging forests also result in a decline in the diversity of tree species, which also makes them susceptible to wildfires, drought, pests, and invasive species.
Tapping into these forests could greatly improve forest health while creating much-needed jobs and wealth in timber-reliant rural communities. The forest products industry is the fifth largest manufacturing sector in Minnesota and vital to the state's economic health. Generating gross sales of $17.8 billion, the industry directly employs 30,500 people, and has a total employment effect of 64,000 jobs. Wood products manufacturing alone employs 10,865 and provides an average annual wage of $49,031. The forest products industry also provides $458 million in total annual state and local tax payments.
Data clearly identifies an important opportunity to grow softwood markets in Minnesota. Based on Forest Inventory and Analysis (FIA) resource data, the state can sustainably support increased harvest of balsam fir, as it has in the recent past. Using more balsam fir in products such as outdoor furniture, will help bolster Minnesota's critical forest products industry by expanding domestic markets.
Using balsam fir is also friendlier to the environment when it's treated by a chemical-free "thermal modification" process. Preliminary experiments have shown that balsam fir that was thermally modified at 180°C experiences less fungal decay than more commonly used tree species (Ponderosa and southern pine) traditionally treated with chemical preservatives.²
However, manufacturers need performance data to better understand how to use balsam fir in their products.
Currently, high quality boards of thermally modified wood are most often used for products, such as solid wood flooring, external cladding (siding), and exterior decking. Thermally modified wood better resists moisture and biological degradation while demonstrating less swelling and shrinking due to weathering and atmospheric moisture changes. (There are some variations depending on species and temperature of the heat-treatment cycle.)
Thermal modification is not the same as traditional wood drying, which is a collection of techniques used to remove water from wood to prevent deformation of wood products in service. Thermal modification actually alters the physical and chemical composition of the wood.
One example of this new product is at the new Bell Museum on the University of Minnesota campus. It was remodeled with cladding (siding) from thermally modified white pine produced in Minnesota.
Ultimately, the current research will provide current and future manufacturers and distributors of wood products with useful information to design more effective products, such as outdoor furniture and high-performance fiberboard. This project will also contribute to enhancing the economic competitiveness of Minnesota's forest products industry by increasing wood harvest and production of new, value-added products.
For more information, contact NRRI Research Program Manager Matt Aro at 218-788-2700 or firstname.lastname@example.org
¹ The recession of 2008 greatly slowed construction and manufacturing, which led to softwoods being harvested well below sustainable harvest levels. In the 2000s, several paper and oriented strand board (OSB) plants closed, and even less softwood was needed. This has generated negative, cascading effects across the vital forest products industry, resulting in fewer jobs and reduced economic output.
² The University of Minnesota Duluth Natural Resources Research Institute (NRRI) and Michigan Technological University recently completed a small-scale biological durability testing study on thermally modified hardwoods and softwoods, including balsam fir. Samples of balsam fir thermally modified at 170°C and 180°C underwent soil block decay testing according to the American Wood Protection Association E10 test standard. This wood was then subjected to pure cultures of four common wood decay fungi (two brown rot and two white rot fungi) for 12 weeks in a sterile environment. At that time, the samples were weighed to calculate mass loss caused by fungal decay.
The balsam fir samples thermally modified at 180°C experienced less decay (i.e., mass loss) than samples thermally modified at 170°C. Surprisingly, the samples thermally modified at 180°C experienced less decay than a common performance benchmark, Ponderosa pine treated with a borate preservative. Further, the samples thermally modified at 180°C also experienced less decay than southern pine treated with alkaline copper quaternary (ACQ) preservative at 1, 2, and 4 kg/m3 target retentions.
While the sample sizes in this study were relatively small, these results suggest that chemical-free thermally modified balsam fir has similar or improved decay resistance compared to traditional softwoods treated with common chemical preservatives. The thermally modified balsam fir samples are also currently undergoing more intense, long-term decay testing at a field site in Hilo, Hawaii.