Will tanoak die out – is it worth saving? Tanoak (Lithocarpus densiflorus) is a California native hardwood tree common in the forest of Northern California and susceptible to Sudden Oak Death (SOD). Since tanoak is not a commercial tree should we just let it die? Tanoak has stumped manufacturers and researches alike trying to find a place for it in the market. It has many first-rate material properties but it has a reputation of being very difficult to dry without creating serious drying defects. The Fifth Sudden Oak Death Science Symposium was held in Petaluma, CA from June 19-22 to address the current knowledge of SOD and devoted a day to shed light on tanoak’s worth. The conference brought together scientists, researchers, and other experts to share information and solutions. More information on the conference presentations can be found at the conference website.
Friday’s session focused on tanoak’s importance and value. Its history and background were discussed first, summarizing its uses, advantages vs. disadvantages and economic viability. This was followed by a discussion of the efforts and studies being done to prevent tanoak trees from succumbing to SOD. The conference did an excellent job of connecting people, bringing people from different fields together to share knowledge and expertise on how to use and protect tanoak.
A presentation, titled “Tanoak as a Forest Product Recourse: Past, Present, and Future”, by John Shelly and Steve Quarles, two University of California forest products experts was presented by Steve, currently employed at the Insurance Institute for Business & Home. This presentation looked at tanoak as a potential lumber resource and compared it to more traditional hardwood species. Tanoak has a rich history as an acorn food source for Native Americans, a source of tannin—a natural chemical used to produce leather from animal hides, firewood, lumber, and pulp for paper. Compared to Northern red oak (a benchmark species), tanoak is stronger and harder, however it is more difficult to dry and exhibits greater tangential and radial shrinkage. More information is available at the UC Woody Biomass Hardwood Utilization webpage. An accumulation of experience from various researches and practitioners has led to core knowledge of best practices. These include avoiding the dark-colored core zone as it cannot be dried without defects, quarter-sawing lumber to improve dimensional stability, and using a drying schedule of air drying to 30% MC followed by a mild kiln-drying schedule. Additionally restraining the movement of wood as it dries by placing a uniform weight of about 150 lbs/ft2 on top of the lumber stack as it dries is known to be beneficial in reducing warp.
Some people are concerned that removing trees that are inflicted with the SOD tree disease pathogen will increase the risk of spreading the disease. Research reported by Shelly however, indicated that the very low risk of spreading the disease when fresh cut wood is transported to different locations disappears entirely once the wood is processed and dried. In fact, using diseased wood my even have some positive benefits. Further information is presented at: http://ucanr.org/sites/WoodyBiomass/HardwoodUtilization/SOD/ .
One such potential benefit is the presence of spalted wood –an early stage of decay—often found in SOD diseased trees. This, combined with the insect tunnels often associated with SOD infected trees creates an appealing aesthetic appearance, often called character wood. This character has the potential to set it apart from other woods. However, it was noted that spalted wood should not be used for flooring because the hardness of the wood with incipient decay is greatly reduced making it too soft for flooring. The interesting appearance of spalted wood can be very attractive in furniture, art, and craft uses. This could create a niche market for SOD-diseased tanoak that is unique, appealing to select buyers.
The participants in the tanoak session also had the opportunity to view an exhibit of a display of pictures, a slide show, and examples of tanoak lumber and finished products (e.g. flooring and furniture). The pictures and slide show depicted tanoak lumber being cut and quartered, then dried. Here the audience could see the preparation process—from forest to flooring—as well as examples of drying effects. Many people’s questions revolved around the option of using tanoak for flooring and its expected durability. Another common topic was the amount of unutilized tanoak in California forests. It is clear that there is continuing interest in finding uses for this tree. The UC experts concluded that with expansion of the market and improvements in the processing we could see a dramatic increase in the use of tanoak across California.
- Editor: Sophie Kolding
- Author: Yana Valachovic
- Author: Pamela Kan-Rice
University of California Cooperative Extension employees, who coordinate most of the sudden oak death-related research and monitoring in Northern California, got a surprise in the spring of 2010, when samples from a monitoring station near the mouth of Redwood Creek near Orick in Humboldt County tested positive for the pathogen. This meant that trees were infected somewhere in the 200,000-acre watershed – more than 50 miles from the nearest known infestation, and farther north than the pathogen had ever been detected in California.
Federal and state agencies, including the USDA Forest Service, CAL FIRE and the Natural Resources Conservation Service, joined forces with UC Cooperative Extension and quickly mobilized resources to control the pathogen in Redwood Valley and halt its spread to neighboring forests. Local landowners have also played a key role.
Yana Valachovic, UC Cooperative Extension advisor in Humboldt County and forestry expert, explained that she and her agency partners had been preparing for this moment.
“We’ve been closely monitoring the disease for years and anticipating a scenario like Redwood Valley, so we were ready to take action and respond quickly,” Valachovic said.
Figure 1. Yana Valachovic sampling vegetation
The UCCE staff leads an extensive sudden oak death monitoring program on the North Coast, and one of their detection strategies involves "leaf-baiting" in streams. Using this technique, they “bait” Phytophthora ramorum, the non-native pathogen that causes sudden oak death, by placing susceptible leaves in strategic locations in North Coast streams. If the leaf baits become infected with SOD, the scientists know that the pathogen is present in the watershed without having to comb the landscape for symptoms.
After they detected the pathogen in Redwood Creek, UCCE acted quickly to pinpoint the source of the waterborne spores, scouring the watershed for the very inconspicuous symptoms of SOD with the help and permission of public and private landowners. By November 2010, the scientists had narrowed the location to Redwood Valley, where they found dead tanoaks and several other infected host plants.
Given its proximity to extensive public, private and tribal lands, the infestation in Redwood Valley was a serious concern. The disease, which was discovered in the Bay Area in the mid-1990s, is found in 14 coastal counties in California, from Monterey to Humboldt, and has infested 10 percent of the at-risk areas in the state. P. ramorum thrives in the coastal climate, and has killed over 5 million tanoaks and true oaks over the past 15 years. It’s still not clear how the pathogen got to Redwood Valley, but it could threaten the dense tanoak forests of the surrounding area, resulting in widespread tree mortality and increased fire hazard.
Much of the on-the-ground effort has been completed by contractors and CAL FIRE handcrews, who have created 100-meter buffers around infected trees by removing California bay laurel (pepperwood) and tanoak, the two hosts that most readily support P. ramorum spore production and spread. Infected plant material has been trucked offsite and donated to the nearby DG Fairhaven Power Company, piled and burned, or lopped and scattered onsite.
Funding from the American Recovery and Reinvestment Act, the USDA Forest Service and NRCS enabled the swift response in Redwood Valley. UCCE used ARRA funds, also known as federal stimulus funds, to hire four people to work on the project, lending stability to the effort.
Landowner support has been critical to the success of the project, according to Valachovic. More than 20 landowners in the valley have allowed monitoring and treatment activities on their properties, recognizing that their cooperation may keep the disease from spreading to other areas.
Figure 2. Chris Lee (UCCE Staff Research Associate) and David Casey
(NRCS Forester) inspecting a treated area
“We couldn’t just stand back and let the disease roll through the forests that we manage, and the landowners understood that,” said Dan Cohoon, who works for Eureka-based Able Forestry, which manages many of the private forestlands in the watershed.
Brandon LaPorte, manager of Cookson Ranch and one of the key landowner collaborators in Redwood Valley, has supported the project from the beginning. LaPorte explained, “We’ve learned a lot about the disease through this project, and we certainly don’t want it getting worse here on the ranch or spreading beyond the valley.”
The first phase of treatment is currently wrapping up, and UCCE is beginning to monitor project efficacy and watch for spread of the pathogen beyond project boundaries. The Yurok and Hoopa tribes will be paying close attention to this effort, as they are only a ridge away from the infestation.
Ron Reed, a Yurok tribal forester, commented, “Oaks are an important part of our culture and history, and we will do what we can to keep sudden oak death out of our forests.
The Redwood Valley project highlights the value of stream monitoring as a detection tool for SOD, but it also demonstrates the ability of agencies and landowners to collaborate swiftly and effectively to protect the region’s forest resources. Maybe most important – regardless of the future course that sudden oak death takes in the North Coast – is what the project shows about the ability of proactive communities concerned about the health of their landscapes to come together, attract the support of state and national authorities, and work to make things better.
The community collaboration is being honored with the Two Chiefs’ Award. The award, which is given jointly by the NRCS and the Forest Service, highlights projects from across the country each year, recognizing exemplary partners who have worked collaboratively to support conservation and forest stewardship. Valachovic will accept the award on behalf of the federal, state, tribal and private partners involved the project at an event in Davis on Wednesday, May 16.
For more information about sudden oak death disease, visit the California Oak Mortality Task Force website at www.suddenoakdeath.org.
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University of California Division of Agriculture and Natural Resources