VIENNA — Through the use of timber sales, foresters on the Shawnee National Forest are fighting to preserve oak stands within the Oakwood Bottoms Greentree Reservoir and Big Muddy River bottomlands in Jackson County, Ill.
“There is currently a timber harvest to treat an infestation of oak wilt [in Oakwood Bottoms] that has affected one of the small stands,” said Brian Thietje, presale forester. “We are creating a buffer area around the infected trees by removing [trees] that are not infected, thus isolating the spread.”
Thietje said the goal of this timber harvest is to stop the spread of the disease in this small section of Oakwood Bottom and prevent it from spreading to larger stands of oaks in the area.
Oak wilt is an aggressive and fatal disease for species in the red oak family (pin, red, and black oaks). Though potentially fatal to white oaks as well, the process is slower or defense mechanisms specific to white oaks can limit the disease damage to sections of the trees rather than the whole. It is caused by the fungus Bretziella fagacearum (previously Ceratocystis fagacearum). The fungus kills oak trees by blocking the water conducting tissues and cutting off flow from roots to the rest of the tree. Once established on site, it is primarily transmitted from infected trees to uninfected trees through underground root grafts.
Oak wilt has been present in southern Illinois for a long period but diverse species compositions and soil characteristics that reduce root connectivity usually limit its damage to individual trees rather than large pockets.
There are three main ways to eradicate oak wilt, all of which all include the establishment of a root graft barrier to break interconnected roots from spreading the disease. These methods, which all include severing root connections between affected and unaffected trees, include use of a vibratory plow or trenching machine, uprooting all stumps within the treatment area, or killing a buffer of unaffected trees around the pocket with herbicide.
“In order to keep the fungus from traveling in the root system from tree to tree, we have [chosen] to put in a buffer around the infestation,” explained Dennis Wilson, district ranger for Hidden Springs and Mississippi Bluffs. “The main goal from this management is to ensure a healthy forest. With the hope of confining the disease to under 50 acres.”
The sub-contractor that is currently conducting the timber harvest is a locally owned business by Cody Robinson, of Robinson Excavating.
“We conduct sealed bids on our timber sale projects,” Wilson said. “The agency has a bid monitoring program that checks for irregular bidding practices to ensure a fair award process. The Shawnee National Forest utilizes the timber sale receipts to put back on the landscape to improve our national forest.”
Types of activities funded included timber stand improvement work, nonnative invasive species treatments, prescribed burning, gully restoration and road maintenance.
Wilson said, over the last 30 years, some of these projects were not getting accomplished leading us to current issues on the forest.
Anyone interested in submitting bids on forest projects should visit the Shawnee National Forest website. Parties can also contact the Hidden Springs Ranger station at 618-658-2111 ext. 1302 or 1317.
Oak Management
The primary goals of oak management on the Shawnee National Forest are to reduce stressors that make them susceptible to insect and disease issues and ensure oak remains the keystone species across the southern Illinois landscape into the future.
In the instance of oak wilt there are several management considerations, improving species diversity to limit the potential for root grafting, and limiting damage to susceptible trees during the spring and summer months when insects known to spread the disease are common. Once a tree becomes infected with oak wilt, it will lose most of its leaves and die within a month. Any trees that are root-grafted to infected trees will die within one to five years.
“When trying to identify oak wilt, look for wilting, browning out of season (spring or early summer), and leaf drop,” Thietje said. “Remove infected trees, especially if you are growing multiple oaks together, since the fungus spreads through intertwined root systems. Brown leaves on your oak tree does not necessarily mean the has oak wilt. It could also be anthracnose, scorch, chlorosis, drought, root stress, or a number of other diseases.”
Root grafts between red oaks are very common, and less between white and red oaks. In stands with a high percentage of red oaks, all oaks are at risk from root-to-root spread. Thus, [oak wilt] infections normally begin with one or two infected trees and radiate out to surrounding oak trees in increasing rate. Similarly, storm damage during the growing season may also create the potential for new infections by insects.
Oakwood bottoms is dominated by pin oak, which falls in the red oak family, and has high tree-to-tree root connectivity. Known locations of oak wilt are currently confined within a 96-acre pin oak plantation, but risk in the surround bottomland forested area is high with red oak dominated forest types comprising 68% of the forested acres and heavy oak mixtures on another 17%.
“This ecologically important habitat supports a variety of game and non-game wildlife species, most notably migratory waterfowl,” said Justin Dodson, natural resources, planning, and monitoring staff officer. “Pin oak acorns are a highly valuable food source for wildlife and contributes significantly to the importance of the habitat. Review of historical aerial imagery in known locations of the disease suggest its presence back to 2007 or earlier at two locations. Those locations continue to see oak wilt caused mortality today.”
Dodson, a certified silviculturist, also explained that leaving oak wilt unmanaged in the bottomlands could have serious ecological implications on wildlife habitat and on pin oak dominated forests in these areas.
“Oak wilt expanse could be much greater than currently realized,” Dodson said. “The 96-acre pin oak infected stand is surrounded by 2,700 acres of red oak species dominated forest within Oakwood Bottoms, and several thousand more acres of federal and other ownership lands adjacent in the Big Muddy and Mississippi floodplain. Therefore, eradicating oak wilt is critical for sustaining the bottomland oak ecosystem.”
