Buckthorn in the Bog

By Jim Reinartz, UWM Field Station director

Buckthorn Control Map

The Friends of Cedarburg Bog have been working hard to control buckthorn in the Bog.

There are three invasive plants that currently pose the greatest threat to the native plant communities of the Bog. Purple loosestrife is a relatively new invader in the marshes surrounding Mud Lake. From 2000 to 2010 the UWM Field Station, with the help of Don Bezella, selectively herbicided the individuals and patches of purple loosestrife that we could find. It eventually became obvious that locating scattered plants among the 8-foot-high cattails in the marsh around the lake was neither feasible nor sustainable over the long term. In 2012 and 2013 we released biological control beetles in patches of Mud Lake purple loosestrife. We will raise and release more beetles in 2014, and will have an opportunity to evaluate whether our previous releases have started to have an effect.

Narrow-leaved cattail, and hybrids between that species and our native broad-leaved cattail, have taken over most of the marsh areas around all of the lakes in the Bog and along the stream crossed by the Field Station boardwalk. There is no known control method for these invasive cattails that would be feasible in the Bog. The Bog will have to live with narrow-leaved cattail.

The most widespread and abundant invasive plant in the Cedarburg Bog is glossy buckthorn, occurring at relatively high density in every part of the Bog except those cattail marshes, which appear to be too wet for it to grow. While there is no hope of eradicating glossy buckthorn from the Bog with known control methods, there is the possibility, with a lot of work, to keep glossy buckthorn at a manageable level in selected parts of the wetland.

The “lot of work” part of this equation is that every stem must be cut close to the ground and treated with herbicide, or an herbicide that will penetrate the bark must be applied to the base of every stem. We have been doing this work mainly when the Bog is frozen and it is easier to get around, and when there is less risk that the herbicide will affect non-targeted native plants. Working in remote parts of the Bog, even in the winter, just getting to and around in the work site can be a daunting task. Thank God or Mother Nature for energetic, fit, mostly young, intrepid people who are deeply committed to the care of our prized natural areas.

In 1991 the Wisconsin DNR and the UWM Field Station began removing buckthorn from selected areas of the Bog that were defined as “exclusion areas”. The idea was to keep representative examples of some of the native plant communities of the Bog relatively unaffected by buckthorn. The strategy is to remove all buckthorn that are big enough to produce fruits, and then to go back to those areas every few years to remove the plants that have grown to fruiting size. If seed production can be prevented for a long enough period, the density of buckthorn in the exclusion areas will decline to a level where long-term control is sustainable. 

Volunteers have contributed substantially to our buckthorn control work, but in general, to accomplish the lion’s share of the work that we have done, those energetic people working long hours need to eat, and groceries aren’t free. As funding was available the DNR and Field Station continued working after that initial 1991 effort through 2008, with major efforts in 1991, 1992, 1996, 2001, and 2006 to 2008. Here enter the Friends of Cedarburg Bog. 

Since 2010 FOCB has raised over $73,000 to apply to this project through grants from We Energies Foundation, the Natural Resources Foundation, and the Knowles-Nelson Stewardship Program. The Wisconsin DNR has continued to provide some funding and crews when they are available, and the entire buckthorn control project in the Bog has been managed by a collaboration of FOCB with the DNR and Field Station.

We have developed a plan for control work in the Bog and identified three main priority areas for buckthorn control. We knew from vegetation surveys done by the Field Station in 1991 and 2006 that the northern part of the Bog had the lowest buckthorn density and also has very nice examples of the mixed conifer-hardwood swamp characteristic of the Bog. We defined one 250-acre priority control area at the north end of the Bog. All but 18 of those acres have had fruiting-sized buckthorn removed at least once. 

The 63 acres of open string bog west of Long Lake was identified as another control priority because that typically-far-northern vegetation type is unique in Wisconsin and is home to a number of very rare plants, including our only Federally Threatened species, the prairie white fringed orchid. 

A third, much smaller (5-acre) priority area was the place where this whole exclusion project started and is located off the east end of the Field Station boardwalk loop. This area is considerably more accessible than the other two and is an excellent example of the more dense string bog habitat in the Bog. 

Two other more minor areas where our control is focused is the area immediately bordering the Field Station boardwalk and the public access path to Mud Lake from Cedar Sauk Road.

Thanks to funding FOCB has generated, work funded by the DNR State Natural Areas Program, and FOCB volunteers, our efforts to provide relatively buckthorn-free areas in the Bog have been very active over the past three winters. In the winter of 2011-12, we again removed buckthorn from the 5-acre plot at the end of the boardwalk and cleared an adjacent area along the trail. In 2012-13 funds raised by FOCB were used to employ a DNR crew to cut and treat buckthorn from 22 acres in the open string bog and another 94 acres at the north end of the Bog. Another 10 acres was cleared by a FOCB-hired contractor. 

This past winter (2013-14) a DNR Natural Areas crew removed buckthorn from 31 acres in the open string bog, and FOCB raised and spent over $21,000 to hire independent contractors to cut and treat 67 acres at the north end of the Bog. In addition to that funded work, FOCB volunteers killed buckthorn along the western portion of the Field Station boardwalk and along the access trail to Mud Lake. Click on the map at the beginning of the article to view the control areas.

FOCB is committed to ongoing stewardship of the Cedarburg Bog as one of its highest priority missions and control of invasive plants is the most important part of that mission. There are few other ways that we can better show our love of the Bog. Volunteer opportunities abound; contact or 262-675-6844.

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