Amur cork tree could cause problems in Dunn County

By LeAnn R. Ralph

COLFAX  —  Do you have any Amur cork trees on your property?

Town of Colfax resident Kathy Stahl, co-chair of the Lower Chippewa Invasives Partnership, wants Dunn County residents to know that Amur cork trees are prohibited by Wisconsin law and are a highly invasive and destructive species of tree.

A number of Amur cork trees have been located in Menomonie.

Menomonie resident Mary Gale asked for help identifying invasive plants on her property from Chris Gaetzke of Dunn County Land and Water Conservation and also of the Lower Chippewa Invasives Partnership, Stahl said.

Gaetzke found a variety of invasive plants on Gale’s property, including common buckthorn, bush honeysuckle, Japanese Barberry, Oriental Bittersweet and garlic mustard. But Gaetzke also saw a large tree that he did not recognize.

Gaetzke learned from a National Parks Service fact sheet that the tree was an Amur cork tree, a non-native tree from Asia that has spread out of control in the eastern part of the United States. He also learned that the tree is prohibited in Wisconsin, which means any Amur cork tree that is discovered must be removed, Stahl said.

The Amur Cork trees are known to shade out everything else around them. The tree also is known to be “alleopathic,” which means it produces a soil chemical that suppresses other plants growing around it, she said.

The Amur cork tree is a heavy seed producer, and the seeds are distributed both by birds and by water. The tree also has a fast growth rate, and it will tolerate full sun, full shade, and a variety of soil pH.

Gale had the large cork tree on her property cut down. The stump measured 30 inches, and Gale and Gaetzke counted 30 growth rings, meaning the tree grew by an inch in diameter each year, Stahl said.

The trees are easier to identify in the winter because the bark of young trees is a lighter tan color than other local tree varieties, she said.

While Gaetzke was walking in Phelan Park in Menomonie, he found cork trees had infested the ridge area and had even shaded out the invasive buckthorn, Stahl said.

Mature Amur cork trees are described as having a soft, gray-brown, deeply furrowed outer bark, and when the outer bark is stripped off, the inner bark is a bright neon yellow.

The female Amur cork trees produce berries that are green in the summer and black in the fall.

Arrival

So how did Amur cork trees end up in the United States?

According to the National Park Service fact sheet, “Amur corktree was introduced to the U.S. around 1856. The Harvard University Arnold Arboretum first acquired the sachalinense variety of the tree in 1901 and the true amurense variety in 1906. By 1933, the New York Botanical Garden reported it to be naturalized in their forests, where it remains today. The bark of the Amur corktree has been prized for its use in traditional medicine in China, India and Japan. The inner yellow bark was used to make a special dye in ancient China and to make yellow paper for governmental and religious documents. In this country, the tree has been used as an ornamental and street tree and is widely planted on college campuses. Demand for the corktree and its varieties as a street tree are increasing as shown by a recent study of urban foresters in Ohio … Amur corktree is invasive in parks and natural areas in New York City and Philadelphia, where it has escaped from plantings. Within 50 years of its planting as an ornamental, it has become a dominant tree in New York City parks. Amur corktree has reported to be invasive in Illinois, New York, Pennsylvania, Virginia and Massachusetts.”

Stahl noted that from the information available from the National Park Service, it appears people are still planting Amur cork trees.

“I suppose if you have only male trees, it wouldn’t be a problem for a street tree. But I wouldn’t want to count on that,” Stahl said.

“Besides, the lower branches very easily break off of the tree, which would make it a messy street tree,” she added.

Stahl said the fast growth rate and the cork tree’s willingness to grow in sun and shade and to tolerate different soils, combined with its somewhat exotic appearance, may have been what made it an attractive tree to plant.

Locations

Because of the Amur cork tree’s ability to shade out native trees and other vegetation, Gaetzke would like to know if there are more of the trees in Chippewa, Dunn, Eau Claire, Pepin or Pierce counties.

Gaetzke would appreciate it if anyone who suspects a cork tree on his or her property would take pictures of the bark, the branching limbs, and the bright yellow inner bark, and along with a description of the location of the tree, e-mail the information to him at cgaetzke@co.dunn.wi.us.

Gaetzke also can be reached at 715-231-6540.

Additional assistance and information is available as well from the Lower Chippewa Invasives Partnership at lcinvasives@gmail.com.

When the tree has been verified, consultation will be offered to the landowner, Stahl said.

The state Department of Natural Resources has some limited funds available for cork tree eradication which can be used on a cost-sharing, first-come, first-serve basis, she said.

If there is a large infestation of trees, it is recommended that the female trees be controlled first. Cork trees can re-sprout from a cut stump, so the stump must also be treated with herbicide, Stahl said.

Lee Schambeau of Menomonie 4 Control is planning to use a variety of control techniques and various herbicides on the trees that have been identified to determine what will be the most effective and least expensive way to control the infestation, she said.