Purgatory Park restoration
Once again, Purgatory Park is abuzz with chainsaws and wood chipper activity. Restoration began at Purgatory Park in a brome grass meadow in 1998; the meadow is now a prairie. The first large buckthorn clearing took place in late 2001, with the second big invasive species cut starting in December 2007 with plans to continue through much of the winter.
New areas under chainsaw attack are all over the park. Various sizes of buckthorn are being removed along the main trails, into adjacent woods and prairie. Non- native honeysuckle is being removed, too. The largest concentration of this second-most-invasive woody species is in a brushland area northwest of the central wetland. Remember, even though honeysuckle is available at nurseries, most varieties are invasive. Please don’t plant non-native honeysuckle near Minnetonka’s natural areas!
Oak ridge
In 2001, the first big buckthorn cut in Purgatory Park took place on the oak ridge, located in the south half of the park and stretching from the east park boundary on Stodola Road to the west boundary at 58th Street West. The ridge feature large old oaks, ironwood, black cherry, hackberry, and more. Since the first cut, many people have commented that the buckthorn has come back worse than ever. This second generation of buckthorn that has grown over the past few years germinated from the extensive seed bank in the soil. Mature buckthorn trees have been dropping black fruits with seed for decades; so when stands are cut, new seedling growth can be tremendous. The dense brush that has re-grown on Purgatory’s oak ridge holds four- to six-year-old saplings and some stump re-sprouts. They seem formidable, but are under control.
Control vs. eradication
Invasive species are controlled by preventing their spread by seed or other means. Young re-growth of buckthorn is not producing seed, so it is temporarily under control—in fact, new seedling germination is using up the seed bank. Literature says buckthorn seed is viable for about six years. By keeping the larger plants under control, the seed bank will eventually be reduced. Eradication means killing all target plants. Eradication of buckthorn in Minnetonka is not possible, but control is possible.
Control techniques
Prairie Restorations, Inc. is doing the current work in Purgatory Park, using three techniques that vary depending on the habitat features that need protection or improvement. Each technique has its advantages. For example, many of the female buckthorn branches with black fruit are dragged to burn piles where viable seed is destroyed. Buckthorn without berries is being chipped on site and blown uniformly into the woods. Wood chips along the trails are aesthetically pleasing, conserve soil moisture, and break down more quickly than other materials. Further from the trails, the cut-slash method is used, where brush is cut into smaller pieces and dropped low to the ground. Brush with soil contact decomposes faster than brush in piles. It also helps reduce soil erosion on slopes and provides habitat for amphibians, reptiles and small mammals.
Restoring remnant native plants
Areas with remnant native trees and shrubs have been marked with yellow or white ribbon-flagging. Work crews have been instructed to avoid these areas. The goal is to hand remove all invasive species that are intermingled with the natives. While this is a tall order that may take years to achieve, some of this work has begun with small groups of volunteers under the direction of natural resources staff. Most volunteers enjoy restoration work, because we are identifying native plants up close and can immediately see the results of our efforts.
The bird thicket
South of the main parking lot and main trail is a special area being restored to a songbird thicket. City staff started to control poison ivy here in early fall 2007. Volunteers flagged native nannyberry, choke cherry, black cherry, gray dogwood and prickley ash being squeezed out by non-native buckthorn. Each of these native species create wonderful songbird habitat, provide flowers for pollinators, and fruit for birds and wildlife. Prairie Restorations cut the woody invasives and treated stumps in December 2007. Wood chips were blown back into the natural area for mulch. A good start has been made to restore the bird thicket, with the hard work completed. Future tasks include spreading the woodchips thinly so wildflowers and sedges can push through; hand-pulling young buckthorn, garlic mustard and weeds; and cutting stump re-sprouts. Thank you to the volunteers who have helped us reach this point.
To assist with these or other park restoration projects, call the city of Minnetonka natural resources division at 952.988.8400.
