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History of the Oak Openings Region
The Oak Openings is a 130 square mile region (Moseley) located in Lucas, Henry and Fulton Counties of Ohio. The region sustains a mosaic of black oak savanna, oak woodland and wet prairie communities that persist on a series of post glacial beach ridges and swales. This area has long been recognized by naturalists as one of Ohio’s preeminent natural regions because of its rich diversity of vegetation. The region harbors more rare species than any other of a similar size in the state and sustains two globally rare communities, oak savanna and wet prairie. Historically the Oak Openings Region may have covered over 300 square miles, extending as far as neighboring Wood county in Ohio and Monroe and Wayne counties of Michigan. Although remnants of habitat do still exist in these outlying areas, conservationists focus primarily on the “Moseley” region. This is a portion of the original area identified by Edwin L. Moseley in his classic 1928 publication, “Flora of the Oak Openings”. At that time, and still today, this area represented the best preserved remnant of Oak Openings habitat in Northwest Ohio and Southeast Michigan. Previous to European settlement the Oak Openings was a pocket of prairie and oak savanna surrounded by the forests of the Great Black Swamp. Early settlers, many whom had just traveled through the dense forests of this swamp, called the area “Oak Openings” for its most obvious characteristics. Black and white oaks were the dominant trees and the landscape was very open and free of underbrush. Naturalist Lou Campbell describes what many settlers must have seen: “A short distance to the west (of Toledo) were hills of sand upon which only oak trees grew, and so sparse were the trees (that) a wagon could be driven in any direction through the patches of forest without the need of hewing a path.” The Oak Openings is entirely confined to the physiographic region known as the lakeplain, a generally flat plain formed under the influence of post glacial lakes. The region is part of a sand belt that extends for approximately 120 miles from northeast of Napoleon, Ohio to west of Detroit, Michigan. The sand was deposited approximately 12,700 years ago as a series of beach ridges formed by post glacial Lakes Warren I, II, and III (Forsyth). These ridges, in some areas 50 feet deep, were deposited over a surface of clay-rich glacial till. In the swales, or depressions between the beach ridges, the sand is thinnest and the till is close to the surface. The rapid permeability and instability of the sandy soils discouraged the development of natural surface drainage. This combined with the impermeability of the underlying glacial till maintained a high water table throughout the year. During late winter and spring, groundwater levels in the swales would often be above the surface, with depths of several feet not uncommon. In late summer and fall, levels would drop and the swales would dry. This extreme oscillation favored herbaceous vegetation, kept the growth of trees and shrubs in the swales to a minimum, and encouraged the establishment of the wet prairies. Fire and the dry sandy soils of the ridges were the two primary process involved in maintaining the oak savannas. Savannas and woodlands experienced periodic fires that promoted a balance between the growth of trees and shrubs and herbaceous prairie/savanna vegetation. In general, the fire favored the growth of the herbaceous vegetation and inhibited the success of the woody plants. Trees remained part of the vegetative structure in these uplands not only because of the better drainage, but also likely as a result of a variable fire frequency, weather conditions and soils. The wet prairies, although primarily influenced by groundwater, were likely effected by fire as well. |
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