What do Wisconsin Oak Woodlands Look Like?

Oak woodlands and prairies are related. In a broad sense, oak woodlands are also grasslands (or graminoid-lands), often supporting rich sods of herbaceous plants set in a matrix that includes grasses and sedges (and often common wood rush). In Wisconsin both oak woodlands and oak openings are lumped together under broader savanna, but oak woodlands are deserve special attention. They are communities of dappled light filtered through oakneither dark forest nor fully exposed. They are as defined by their herbaceous vegetation as they are by their trees, but very seldom do oaks still coincide with intact, old-growth woodland sod. Are truly intact woodland sods as rare or rarer than prairie sods? Perhaps. Three very common and widespread historical factors have driven the decline of oak woodlandgrazing, fire exclusion, and forestry practices. The best remnants are found where one or more of these factors was muted various factors–access, wind blowing leaf litter clear. All too often, opportunities to restore woodlands go unrecognized in favor more open savanna types or management of closed forests. In this post my aim is to show some small fragments of oak woodland, mostly degraded but still recognizable as such. One thing to notice is that the vegetation is low and grassy, regardless of time of year. I’ll be adding to this post over time.

This remnant oak woodland at the Army Lake Boat Launch in Walworth County (the foreground is paved now) is / was truly remarkable. Located on a knoll surrounded by open water and peatland, it was likely minimally disturbed before an access was created in the 1950s. It’s possible that the topography and openness to the lake exported leaf litter that would have otherwise smothered its sod. Mesic and situated on silt loam soils, it supports huckleberry and velvet-leaf blueberry.

An image of the old growth sod of the Army Lake Woodland–a matrix of common wood rush, savanna running sedge, Pennsylvania sedge, Robin’s plantain, wood betony, yellow stargrass, and common blue-eyed grass. Other areas are co-dominated by species including bastard toadflax, forked aster, Carolina vetch, pale vetchling, New Jersey Tea, and midland shooting star.

Another bit of Army Lake Woodland sod, here full of two-flowered Cynthia, Carolina vetch, and bastard toadflax.

This is Summit Bog Island in Waukesha County, a knoll of silt loam soils surrounded by peatlands. It is moderately compositionally and structurally degraded, but unlike most areas, the understory has not yet become choked with invasive shrubs. It remains graminoid-dominated. The main issue is the slow encroachment of ironwood, black cherry, and shagbark hickory. Here too, at least some potentially smothering leaf litter is exported by wind.

A view of the sod at Summit Bog Island. Visible are velvet-leaf blueberry, Pennsylvania sedge, savanna running sedge, red vine honeysuckle, Parlin’s field cat’s-foot, shining bedstraw, and grove sandwort. Carolina vetch, pale vetchling, Maryland black snakeroot, bastard toadflax, showy goldenrod, arrow-leaved aster, and poverty oatgrass, northern hawkweed, common wood rush, rough hawkweed, and broad-leaved panic-grass, are among the other species present, but much appears suppressed here due to conspicuous severe deer browse. The “island” knoll is a hub connecting all the deer paths through the surrounding peatlands.

This oak woodland on a northwest-oriented ridgetop dolostone point in the Trempealeau County. Here Pennsylvania sedge, savanna running sedge, poverty oatgrass, and broad-leaved panic-grass are among the graminoids. Yellow pimpernel, Carolina vetch, and northern bedstraw are abundant. Woodland sunflowers are atypically benign. A more red oak-domianted north slope supports low bush honeysuckle, broad-leaved panic-grass, poke milkweed, yellow lady’s slipper, and northern bedstraw.

This Iowa County oak woodland over sandstone suffers somewhat from excessive leaf litter accumulation, but Pennsylvania sedge and Swan’s sedge are both present. Forbs include midland shooting star, northern hawkweed, rough hawkweed, hoary frostweed, stiff aster, showy goldenrod, and bastard toadflax. White oak grubs/seedlings are abundant, as they often are under a high oak canopy where the understory hasn’t become too full of brush and small trees.

Oak woodland in historically heavily grazed area at the toe of an esker in Walworth County. Nonetheless, the graminoid structure is retained and there is much white oak regeneration. Midland shooting star, alumroot, Pennsylvania sedge, Swan’s sedge, and common wood rush are present.

Woodland on south slope under white and red oak (canopy was present in 1940 as well) at another “island” woodland remnant near Army Lake in Walworth County. This island is a kame or kame-like structure and consists of rocky-domomitic till. Prominent graminoids are savanna running sedge, Leiberg’s panic-grass, Pennsylvania sedge, poverty oat grass, slender wheatgrass, and common wood rush. Large yellow false-foxglove, lead plant, bastard toadflax, showy goldenrod, sky-blue aster, shining bedstraw, northern bedstraw, kittentails, midland shooting star, Robin’s plantain, and early goldenrod are also present.

Historically heavily grazed oak woodland over sandstone in Richland County. Pennsylvania sedge, poverty oat grass, savanna running sedge, hoary frostweed, prairie pinweed, rough hawkweed, and northern hawkweed are among the remaining flora. White oak seedlings/grubs are dense.

An open portion of an “island” (thicketed areas were historically more open) between Lulu and Eagle Spring Lake in Walworth County. Carolina vetch, grove sandwort, alumroot, and broad-leaved panic-grass are among the species present.


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