Oak Wilt Control on the Chequamegon-Nicolet National Forest Using the Root Rupture Method (USFS)

Cost effective and operationally feasible control of oak wilt in a forested setting.

Lakewood, Wisconsin

Numerous sites within the Lakewood/Laona Ranger District, Chequamegon-Nicolet National Forest

US Forest Service

Central hardwoods

Alvar Woodland

AVb (Acer/Viburnum)

ambrosia beetles

oak decline

Kennan fine loamy sand / Padus sandy loam

1925

As noted above under Stand Origin, these stands originated in 1925, when they were released by the last large landscape-level fire to burn through the area. The regenerating stands were a mixture of aspen, paper birch, red oak, and red maple. In the 1970’s initial entries focused on removing aspen, which was mature and highly-valued for pulpwood. Second entries in the 1980’s continued the removal of aspen- as well as much of the paper birch. In the late 1990’s and early 2000’s the focus was on density management and improving stand quality by thinning the oak and culling out much of the red maple. The consequence of this management history was a landscape of high quality, high value oak sawtimber and relatively little within stand species diversity. This has rendered the stands vulnerable to oak wilt and other pests, such as two-lined chestnut borer. Another concern is that the stands are now over 90 years in age. Our management has, generally, been successful in recruiting advanced oak regeneration in preparation for final rotation. Recognizing the consequences of past management (reduced within-stand diversity), we have also begun to foster the establishment of conifers (mainly white pine) to meet long-term objectives of mixed pine-oak stands.

Greater than 80% of the total basal area in the treatment areas is northern red oak.

Quercus rubra (northern red oak)

80%

Variable. Typically 100-130 ft2/acre, 12-18 inches average DBH, and with a normal distribution.

The one common element across all treated sites was the presence of oak wilt infection centers that threatened to spread to adjacent oak trees. Another complicating factor is the presence of two-lined chestnut borers, which can sometimes confuse the diagnosis. Local deer densities are approximately 10-15 deer/square mile.

Oak wilt was first identified on the District in 1997 at Boulder Lake Campground and was effectively treated with a vibratory plow the same year. In the summer of 2001, oak wilt was discovered in an active timber sale unit near Waubee Lake. Many infection centers were subsequently found scattered over a large area in the vicinity. Due to the uneven topography and rocky conditions at many of the sites, conventional treatment with a vibratory plow wasn’t feasible. Manfred Mielke, a pathologist with Northeastern Area State and Private Forestry, proposed an alternative method of treatment for use in a woodland setting. It has, since, come to be known as the “root rupture method”. This method involves cutting and removing infected and adjacent healthy trees and then using an excavator to rip out and overturn the stumps and root wads. In doing this, the root grafts are broken and diseased tissues are isolated from neighboring healthy oaks. To our knowledge, this method had never been attempted anywhere else prior to being developed on the Chequamegon-Nicolet. We treated the infections in this manner in 2001 and 2002 and found the treatments highly effective. However, we didn’t begin annual detailed on-the-ground monitoring until 2004 and so precise figures of the effectiveness prior to that time are not available. We have continued to treat oak wilt infections in the area annually from 2004 through 2017.

To contain infection centers early- before they can spread into surrounding areas. To reduce the amount of oak wilt inoculum that can be spread overland by Nitidulid beetles. To complete these treatments in a cost-effective manner. To complete the work in a manner that is operationally feasible. To prepare the sites for natural regeneration to a mixture of species.

A landscape dominated by even-aged oak and aspen. Oak sawtimber and aspen pulp are the main timber objectives and upland game and non-game species benefit from this management. Oak wilt spread has been greatly limited. In the long-term, we’d like to reestablish red and white pine throughout the area in an effort to move the landscape closer to its historic condition and increase resiliency to insect and disease.

Find the original infected oak and mark it for removal. First Ring: Add the DBH of the original infected oak to the DBH of the nearest neighboring oak in question. Using the chart below, mark the tree if it is within the limiting distance shown. If there is a clump of 2+ trees, add each DBH to the total when figuring out your limiting distance (i.e. clumps will have a higher probability of being within the limiting distance). Second Ring: Once the first ring is completely marked, begin a second ring. This time instead of using a single oak tree in the middle, use multiple oaks on the outer edge of the first ring to determine limiting distances for the second ring of trees. Only mark non-oak species for removal if they are merchantable and within 5 feet of an oak that is being removed (due to treatment of stumps as seen below in design and mitigation measures) When marking trees, use yellow paint and paint a full ring at DBH height (2” thick) as well as a 12” long stump mark.

• forest health

Between 2004 and 2016, 239 separate sites have been treated using the root rupture method. A typical treatment area resembles a large canopy gap or a small group selection. About 29,000 oak stumps have been dug up as part of the treatments. This results in notable mineral soil exposure in the treatment areas. Surprisingly, most of the treatment areas are heavily stocked with advanced oak regeneration within a few years after the treatment. As noted earlier, previous shelterwood preparatory cuts have been successful in accruing oak regeneration in the understories of the stands. The removal of the overstory and soil disturbance eliminates much of the competition that would normally impede the development of the oak seedlings and saplings. At the same time, we’ve seen robust regeneration of seed origin seedlings from a wide variety of species ranging from paper birch to white pine. Thus, the regenerating pockets are typically quite diverse.

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Monitoring of the treatment sites has shown that, approximately 71% of the time, no infections were found for a period of four years after the initial treatment. On those sites in which border trees subsequently wilted, follow-up treatments were conducted. Greater than 90% of the time, the infection was no longer active for a four year period following two treatments or less. Normally, within 4-5 years following the treatments, the sites are heavily stocked with a diverse assortment of early to mid-successional species > 6 feet tall.

Under the contracts, the purchasers have bid on the value of the timber and, at the same time, submitted a bid for the cost of the stump removal. The value of the timber has offset the cost of the stump removal and surplus funds have been used for restoration work elsewhere on the Lakewood/Laona District. Approximately $1.3 million in gross revenue was generated from these sales. The cost of the service work funded by the sale of the timber has been just under $250,000. The treatments have been completed over this 13 year period for a net gain of a little over $1.1 million.

All known sites are monitored for a minimum of five years. As noted, some of the treatments are not successful on the first try. Likewise, as we go about our monitoring, we find new or previously unidentified infection centers. Most of these will be prepared for treatment and it is our intent to continue putting out these “spot fires” in the future. Over time, the distribution of known infection centers has been gradually reduced to a core area. We know that the goal of oak wilt elimination is unrealistic in our area, but it is our hope that we can limit the amount of contagion by limiting its distribution. Our best success has always been in those sites that have only recently become infected. Much like firefighting, the success rate has been the greatest in the areas with the smallest perimeters.

This treatment method has been the most effective when applied in the early onset of infection. Most treatments have been effective in cases where there was one wilting oak at the infection center. Other sites, with multiple dead and wilting trees at the center, often require subsequent treatments to control the infection. At times, we’ve found oak wilt to be an elusive target. In some cases, we identify and treat an infection, monitor it for several years and find no signs of infection. Then, after several years without symptoms, a tree on the edge of the treatment site wilts. Was this a new overland infection created by beetles? Or did the infection somehow creep across the control line? Treating and tracking numerous treatments presents accounting challenges. For example, two sites may be located 100 meters apart and have separate identifiers. Both of them may be treated, resulting in two small openings that are separated by a small area of trees. Later, one of the sites may require a follow-up treatment, which effectively creates one larger opening. If, at a later date, it is determined that another follow-up treatment is needed, it creates a dilemma: which treatment site was effective? Were they both ineffective? Likewise, it can sometimes be difficult to determine whether the treatment was ineffective or if there was a new overland infection caused by beetles. For example, if, following treatment, a wilting tree appears 50 feet from the edge of the treatment area, should it be viewed as a new overland infection- or as a failed treatment? Situations like these complicate our ability to definitively state whether some treatments were or were not effective. It’s not all black and white. Still, after 15+ years of treatments, there is little question that this method is highly effective.

oak wilt, silv-FH, NIFA, stump removal

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John Lampereur

Lakewood/Laona District Silviculturist

Chequamegon-Nicolet NF

John is the District Silviculturist on the Lakewood/Laona Ranger District of the Chequamegon-Nicolet National Forest. He has been in this role since 2003. Prior to this, he worked as a forester for the US Forest Service in Washington and Minnesota before returning to his home state as a planner in 1999. He is a 1990 graduate of the University of Wisconsin at Stevens Point (B.S. Forestry) and of the Pacific Northwest Region’s Silviculture Institute (1996). He has worked for the Forest Service since 1989 and has been a Certified Silviculturist since 2001.