Mixed Hardwoods
in Southern Wisconsin
The
mixed hardwood forests in southern Wisconsin are a highly diverse mixture
of a very wide variety of broadleaf tree species. These forests occur
along a transition between forests that are known as northern hardwoods
and those that are known as central hardwoods. Since the management of
northern hardwood stands is discussed elsewhere on this website, this
section will focus on the unique characteristics and management of those
stands in southern Wisconsin that are dominated by central hardwoods.
The successional pathway in central hardwoods in southern Wisconsin ends with a similar condition as northern hardwoods dominated by highly shade tolerant sugar maple with associated species including red maple, basswood, and white ash. However, it is the earlier successional stage of the central hardwoods that are distinctly different from the northern hardwoods. Common sun-loving early and mid-successional species in the central hardwoods include shagbark and bitternut hickory, walnut, butternut, cherry, and a variety of oak species. Central hardwoods that have been degraded through grazing or high-grading (harvesting of only the best trees) may also include aspen, white birch, box elder, and red cedar. Degraded central hardwood stands commonly also contain a dense shrub layer that can impede the establishment of regeneration.
Central hardwoods grow on a wide variety of site types ranging from dry to mesic uplands. Site quality can influence the species composition on a site, but more importantly, site quality significantly impacts which species will perform well on a site. Dry sites favor the development of black oak, pin oak, bur oak, white oak, and the hickories. Dry-mesic sites favor red oak, white oak, red maple, basswood, and the hickories, while mesic sites favor sugar maple, basswood, and red oak. For more details on the development of central hardwood forests, see the USDA Forest Service Manual of Silvics.
Management options in the central hardwood stands of southern Wisconsin are as diverse as the species composition. In fact, under many circumstances, the preferred management option can in large part be driven by the species composition. Stands dominated by the more shade tolerant species, such as sugar maple and basswood, can easily be maintained through a single-tree selection system with canopy gaps.
How a selection system is implemented is outlined in the section on northern hardwood forests. Alternatively, stands dominated by the early successional sun-loving species, such as oaks, hickories, or walnut can either be managed with even-aged techniques to maintain the timber type or can be managed with a single-tree selection system to convert the site to shade tolerant species. Even-aged management in central hardwoods would involve beginning thinning operations when the diameter (dbh) of the dominant trees average 5 inches and should continue once every ten years. Younger poletimber stands should be thinned to between about 45-to-60 ft2 and sawtimber stands should be thinned to between about 60-to-75 ft2. Thinning (the removal of some of the trees to promote the growth of the remaining trees) should focus on the removal of poor quality, slow growing, and unhealthy trees while retaining the best quality, healthiest, and vigorous trees as well as releasing growing space for the crowns of the best crop trees. At between about 90-to-130 years old, the even-aged hardwood species are typically maintained with a shelterwood regeneration harvest.
Brush control during regeneration treatments may be particularly important in central hardwood stands. Without some form of regeneration harvest or major disturbance, central hardwood stands will eventually decline and convert to more shade tolerant northern hardwood condition. Penny and Gary Shackelford of Rock County have chosen to use shelterwood techniques in the hardwood stands on their landholdings in southern Wisconsin in order to maintain the biodiversity present in the early successional stands.
For more details on managing central hardwoods, see the DNR Silviculture and Forest Aesthetics Handbook.