Oak savanna restorations an environmental boost
OSHKOSH – At one time, vast areas of the southern half of Wisconsin were covered by oak savannas — prairies with many trees but not dense enough to create a canopy, thereby providing an ideal habitat for wildflowers and numerous beneficial insect, bird and mammal species.
Although only a few remnants of those natural land expanses remain undisturbed today, enough is known about them to justify restoration projects that can provide rewards such as healthier soils and cleaner water along with displays of native wildflowers and wildlife populations on sites such as one's backyard or “a back 40,” according to Craig Maier, the coordinator of the Tallgrass Prairie and Oak Savanna Fire Science Consortium.
Maier, who lives on a farm near Merrimac, was one of the speakers at concurrent sessions during the 21st annual Toward Harmony with Nature conference sponsored by the Fox Valley Area chapter of Wild Ones. The organization is an avid promoter of native plants and landscapes.
Types of oak trees
In his profession, Maier is involved with the networking to promote awareness, understanding, and adoption of fire science on landscapes in the Upper Midwest. He pointed out that most of oak trees — white, burr, and swamp white but not black — can tolerate periodic fires because of their deep bark and a concentration of any wounds in the wood.
Oak leaves, which are heavy with lignin, provided native Americans with fuel for fires, Maier stated. In that respect, oaks are counter-culture today because of a pervasive “put out the fire” mentality, he remarked.
While prairie grasses should have a burn every year, Maier recommended burning an oak savanna every three to five years. He said oak trees need about 10 years of growth to be resistant to the effects of fire.
Many native oaks were located close to waterways, were beneficial to Monarch butterflies, and were also proximate to turtle crossings on burned uplands to lay eggs, Maier indicated. Scientists agree that oaks can be hosts to 557 different species of caterpillars alone, followed by cherries (456), willows (455) and birches (411).
The early season catkins (flowers) on oak trees are beneficial to several insect species, on which birds feed, while fungi also thrive in the locality, Maier pointed out. He also mentioned that hemi-parasitic plants such as the fern leaf false foxglove depend on oak trees.
Migrant songbirds such as the yellow-throated vireo also appreciate the scattered canopy of an oak savanna, the diversity of associated plant life, and the open understory of plants, Maier continued. In the autumn, the acorns provide food for ducks, quail, turkeys, grouse, bear, deer and squirrels.
Making a pitch for value of controlled fires on oak savannas, Maier reported how bees returned to 1,500 acres that were restored in northwestern Illinois and how milkweed and butterfly weed are important species for the site. He noted that a new federal program authorizes payments for the establishment of pollinator strips on cropland.
Restoring a site
An ideal restoration site should have 18 inches of dark soil, including clay, and can be in virtually any use or condition today, Maier indicated. Getting historical information about the site is available through the www.sco.wisc.edu website, he noted.
If the site is not regularly cropped land, it needs to be cleared of existing vegetation, including trees of other species and most especially the invasive shrubs such as honeysuckle and buckthorn, Maier emphasized. He suggested that a site with a history of growing corn is likely to have adequate fertility at the time of planting.
Planting density of oaks — certainly not approaching 600 to 800 saplings per acre — can be designed for long-term results of isolated trees to a dominant stand, Maier indicated. At sites with good growing conditions, be aggressive in thinning even after a successful planting of about 100 per acre, he advised.
Where possible, plant in curved rows on the north side of a slope, Maier advised. He would intersperse some native shrubs such as serviceberries, wild plums, and witch-hazel, introduce such tall standing plants such as milkweed and lead plant, and include prairie or wetland species, depending on the site.
An option is the agri-forestry concept — rows of trees surrounded by cool season grasses that can be harvested or grazed by livestock, Maier said. A related concern is to protect the young trees from browsing by deer until they reach a sufficient height.
At the moment, there is not a good market for soft wood species in southern Wisconsin, Maier warned. Regarding oak wilt, he said red and black species are the most susceptible.
For more background, read the “Burr Oak Manifesto” book or join a local Prairie Enthusiast chapter, Maier suggested. “Above all, be patient. It's slow.”