Background: Oak woodland and oak savanna are fire-developed vegetation communities that historically made up much of the land cover in the Midwest. These communities supported hundreds of understory plant species and abundant wildlife. Wildfire suppression, intensive livestock grazing, conversion to agriculture, and invasive species have all taken a toll on Wisconsin’s oak woodlands and savannas. Although southern Wisconsin still harbors thousands of acres of remnant oak stands, the present physical structure of most of these remnants is no longer indicative of historical conditions. Consequently, many of these degraded remnants no longer offer habitat features adequate to support a large range of different wildlife, and the species that once utilized oak woodlands and savannas for their habitat needs are now either in decline or at-risk of extinction. Fortunately, the majority of remnant oak stands in the Midwest are still in recoverable condition.
Initial Site Condition: Original survey records from 1832 described the historical condition of this 25-acre remnant site as oak woodland dominated by ‘timber oak’ (most likely white oak, Quercus alba) interspersed with burr oak (Q. macrocarpa). Several oaks in this stand had their growth rings cored and were found to be between 175 and 200+ years of age. Although oaks still dominated the stand’s overstory, decades of fire suppression and species invasions contributed to a condition where the midstory and understory had become overgrown with box elder, elm, cherry, buckthorn, honeysuckle, and brambles, and the understory had completely disappeared (above, left photo). Oak regeneration was negligible since oak seedlings were continually being shaded out by the dense invasive shrubs dominating the understory. This remnant was still in recoverable condition, though it had passed the threshold beyond which simply returning fire to the system would be adequate to reverse its degraded condition.
Actions Taken: The midstory and understory had to be cleared of invasive shrubs and tree species not representative of historical oak woodlands (above, second photo from left and second photo from right). A portion of these trees were used to create snags, nurse logs, basking logs, and other wildlife habitat structural elements. The predicted (and observed) initial response of this system to tree and brush removal was a flushing of the invasive shrub seed bank due to higher light transmission to the forest floor. This reinvasion was suppressed with a combination of prescribed fire and foliar brush treatments over the course of several consecutive growing seasons to exhaust the invasive species seed bank and diminish reinvasion potential. A similar sequence of treatments was concurrently required to suppress thistles, bur dock, and other weedy herbaceous species that had invaded the site. The site was planted in autumn 2009 with 95 herbaceous species at a seeding rate of 6 lbs/acre. The site is now burned semi-annually to maintain the park-like, open character of oak woodland.
Outcomes: The initial trajectory of continuing degradation was reversed and the site now has been restored to its historical condition, including a well-established groundlayer of grasses, sedges, and wildflowers (above, right photo). Moreover, several at-risk wildlife species have repopulated the site, including Red-Headed Woodpecker (WI Threatened), Brown Thrasher (WI Special Concern), and Prairie Vole (WI Special Concern) and are becoming more common in the area. Oaks are beginning to regenerate with an abundance of seedlings and saplings that now populate the understory. Management is ongoing, but has greatly diminished in intensity and cost, as the site is now self-sustaining as long as it continues to regularly experience prescribed fires.
Had management not occurred, the overstory oaks would have died out without being replaced, and the site would have transitioned to an overstory of mesic forest hardwood trees for one generation as the midstory matured, after which it would have become a buckthorn monoculture incapable of supporting either wildlife, timber production, or outdoor recreation.