Southern Wisconsin historically had forests and woodland cover of 30-50% depending on how you define a forest. Generally, the area was considered an “oak-hickory” ecosystem, but depending on the location, hydrology and soils, other species may predominate. For instance, on certain north facing slopes of steep bluffs, white pine and paper birch can be found. These trees were not planted by early settlers. They are remnants from the earliest retreat of the glaciers when a northern coniferous forest was widespread. As the climate became warmer and drier, pines and birch died out and were replaced by oaks and hickories – except in these locations where the microclimate remained as it was.
The forests and woodlands of Wisconsin have generally deteriorated rapidly in the past fifty years as cattle have been moved from pasture to barn and human activities other than hunting have decreased. Perhaps 90% of the area once covered by forests have been converted to agriculture and of the areas that remain, only a very small percentage could be considered healthy. Most forested areas and woodlands today are thick with brush. In most cases, the brush is European buckthorn and species of honeysuckle. But native plants such as prickly ash and boxelder can also be considered invasive.
The invasive species of buckthorn and honeysuckle have pushed today’s woodlands to the brink of collapse. Historically, the ground cover in woodlands consisted of “spring ephemerals. These species, such as spring beauties, Dutchman’s breeches, and rue anemone, sprout and bloom before the native trees and shrubs leaf out. Buckthorn and honeysuckle are the first woody plants to grow leaves in the spring and the last to lose them in the fall. Thus, when they begin their invasion, spring ephemerals are the first to go. As they take over, dense shade destroys remaining ground covers like sedges, ferns, and grasses. The result is bare soil under the canopy and a nearly lifeless forest.
At the time of settlement, the woodlands of southern Wisconsin were primarily open and park-like. This condition was maintained by periodic fire and herbivory by bison, elk and deer. The diversity of these ecosystems can be quite astounding. Trees, shrubs, grasses, sedges, wildflowers, and ferns are found in abundance. The process involved in taking a woodland or forest preserve that has been impaired by invasive species to one that resembles the healthy state at the time of settlement is a long one. In fact, it should not be considered a process with an end goal in mind, but rather a change in behavior that will last the lifetime of the land owner and hopefully beyond.
The early stages of woodland restoration involve removal of invasive woody species. Primarily this is done with mechanical means, but in some circumstances it can be done by reintroducing herbivores – usually that means cattle or goats in today’s world, but bison and elk would be even better. For most land owners, the only practical method is mechanical removal.
It is possible to bring a woodland back to a certain level of health simply by removing woody invasives. In some cases, native ground covers will return on their own. But more often than not, removing woody invasives will allow herbaceous invasives like garlic mustard to come in. Ultimately, the only way to hold off garlic mustard is to remove enough trees to allow 25-50% sunlight penetration and to replant with native grasses and sedges. Once grasses and sedges become established, one can manage garlic mustard with a broadleaf herbicide and then begin reintroducing native broadleaf plants like wild geranium and columbine.
Once native ground covers become established it is time to reintroduce fire. From that point onward, your woodland should be on a positive trajectory. But, always remember, as mentioned early on, forest restoration is a process that must become a behavior. Periodic burning and active husbandry are required in perpetuity.