Thursday, October 7, 2004

Plant of the Day: Sugar maple, Acer saccharum

Sugar maple is a dominant tree species in many areas of eastern deciduous forest. It ranges from Nova Scotia west to Minnesota, and from southern Canada south to the Appalachian Mountains. In the Great Lakes states, it is found on a variety of soils; but it does best on well-drained loamy soils, and is seldom found on dry shallow soils or in swamps. It is known for its spectacular red, orange, and yellow leaves in the fall; its sweet sap, used to make maple sugar and syrup in the late winter; and its fine-grained wood, prized for building furniture.

As we skirted Madison, Wisconsin, first pedaling broadly to its north, then to its east, we encountered more of the diverse glacial landforms that Wisconsin exhibits. Sun Prairie, which is northeast of Madison, lies in the midst of one of the more impressive drumlin fields in the world. Drumlins are glacial landforms that occur in large groups, each with the appearance of a surfacing whale, all oriented in the same direction. Drumlins formed when ice overrode the preglacial landscape, streamlining the bedrock or previously deposited glacial drift into elongated forms the shape of an inverted spoon. The steep end of the drumlin is on the side from which the ice advanced, while the more gently sloping end points the same direction the ice was moving. They added variety to the cycling through this area, given the steep climbs and descents we made crossing over the drumlins that the highway traversed.

Farther to the south, beyond Whitewater, Wisconsin, we found more rolling country to pedal through in the Kettle Moraine Interlobate area. When the ice advanced across what is now Wisconsin, it was channeled into major lowlands, including those now occupied by Lakes Michigan and Superior, and Green Bay. The uplands of the Door, Bayfield, and Keweenaw Peninsulas impeded the flow of the ice, causing it to split into several different lobes as it moved across the state. [The resistant rock that makes up the Door Peninsula is the same rock unit that forms Niagara Falls—it outcrops in a broad ring centered on the Michigan Basin.] Where the Michigan and Green Bay Lobe butted up against each other in the eastern part of the state, a series of interlobate moraines formed as the ice disintegrated during meltback. The topography is hummocky with many steep slopes, and includes an array of glacial landforms. Although many of them are much lower, some of the moraines are impressive, rising 250-300’ above the surrounding terrain. Kames add to the complex topography; they are sandy, conical hills that formed when streams flowing on the ice ran down through cracks, depositing their sediment in piles at the base of the ice. Eskers were also constructed from sand and gravel, but by streams flowing through tunnels at the base of the ice rather than down through vertical cracks. They are evident as sandy ridges that snake through the modern landscape, often oriented parallel to the direction of ice movement. Lakes are particularly common in the Kettle Moraine area; in fact, it is named for the frequent kettles, or lakes that formed when sediment was deposited around stranded ice blocks as the ice receded (like the prairie potholes).

Because of the varied topography in the Kettle Moraine area, the vegetation that existed before Europeans settled the area was very diverse. On drier soils in the southern part of the region, bur oak savannas and forests dominated by black and white oak were common. Kettles supported many different kinds of wetland vegetation: swamps dominated by conifers; fens, or alkaline wetlands; sedge meadows; and marshes. In the northern part of the region, where fires were less common and the soils were moister, forests dominated by sugar maple and basswood stretched across the landscape. Today, with fire suppression and conversion of much land to other uses, some of these vegetation types are much less common. Kettle Moraine State Forest, which we biked through today, and other preserves play an important role protecting the remaining natural areas.

In Illinois, we made a broad bypass around Chicago, taking us near the small town of Sugar Grove. The name for the town is a translation from the Potawatomi name for this region, so named because of the abundance of sugar maples, which provided maple sugar first for native settlers of the area, then later for Europeans. Near Sugar Grove, we rode right by Bliss Woods, which preserves a small remnant of the natural environments that were widespread when Europeans settled this area. During the Pleistocene, streams running at the base of the ice deposited sand and gravel in a linear ridge, or esker, that now snakes through the reserve. Although part of the esker has been removed by a gravel mining operation, the piece that remains in place illustrates the microclimatic differences between north and south facing slopes and, consequently, the contrasting plant communities they support. In the northern hemisphere midlatitudes, the sun is always in the southern half of the sky during the hottest part of the day. Southwest-facing slopes are relatively hot and dry because they are exposed to direct sunlight during the mid-afternoon, while north-facing slopes are shaded from the intense heat. Plants that tolerate drier conditions, like oaks and hickories, are more common on southwest-facing slopes. In contrast, north-facing slopes support plants with greater moisture needs, like sugar maple and basswood. Even the perennial herbs that carpet the forest floor with a blanket of colorful blooms in the springtime differ between southwest- and north-facing slopes.

Our route kept us just far enough south that we couldn’t see much of Lake Michigan as we skirted the urban areas along the lake. We rode just south of Indiana Dunes National Lakeshore, not only a beautiful spot, but also one of great ecological significance. The national preserve includes nearly 25 miles along the coast of Lake Michigan and encompasses a diversity of environments—beaches, sand dunes, bogs and other types of wetlands, and forests. The park even includes one of the easternmost remnants of tall grass prairie. Lake Michigan formed near the end of the last glacial period. As the ice slowly melted, water filled in the low areas that are now the Great Lakes, ponding in front of the receding ice margin. The history of the lake is complex, and water levels fluctuated many times, gradually lowering the lake level. Today, four main dune complexes are evident behind the beaches. Each dune reaches 150-200’, with numerous wetlands occupying the depressions between dunes. Although mature oak forest occupies the older two dunes, the younger dunes are still geomorphically active. They support a diversity of vegetation, representing a wide range of successional stages. The noted geographer and ecologist, Dr. Henry Cowles, studied plant succession on this dune sequence over 100 years ago, which formed the basis for his landmark work on dune succession.

Strategically located on the southern shore of Lake Michigan, Indiana Dunes serves as an important feeding and resting area for migratory birds. More than 350 species of birds have been recorded in the reserve. The numerous wetlands provide valuable habitat for water birds. One area within the national lakeshore supports a great blue heron rookery—a place where herons congregate and nest in trees surrounding wetlands during the breeding season. They are majestic wading birds that patiently stalk unsuspecting fish, then quickly spear them with their long bills.

South of Indiana Dunes National Lakeshore, we rode through Moraine Nature Preserve, a state-own reserve that protects forested land in an area of rolling topography. The more rugged terrain is part of the Valparaiso Moraine, deposited across northern Indiana as the Michigan lobe melted back during the last glacial period of the Pleistocene. The topography in this area is reminiscent of that we encountered in the Kettle Moraine area—with ridges and potholes shaped by the disintegrating glacier.

A little farther to the east, we rode through Amish country. Amish Acres, near Nappanee--a small town we cycled through—preserves an 80-acre working farm and homestead that is listed on the National Register of Historic Places. The complex includes the Round Barn Theatre, a round barn that was restored in 1911, and that serves as a theatre for the performance of Amish-themed musicals. We saw several horse-drawn buggies as we rode through this area.

After we crossed into Ohio, we encountered the flat area west of Lake Erie, known as the “Black Swamp”. It was formed during glacial times when the predecessor of the modern Lake Erie was much larger. As the margins of the glaciers melted back, water often ponded in front of the ice where the land surface sloped back towards the ice. Eventually such lakes drain, although it may take thousands of years for that to occur—as is the case with the Great Lakes. Once the lake level drops and the lake starts to shrink, extensive areas of flat glacial lake plains become exposed. The flat landscape results from both infilling of deep portions of the lake with fine sediments when water covered the area, and beveling the higher parts of the lake bottom by waves. Throughout part of its complex history, predecessors of Lake Erie extended farther inland, with lake levels at one point over 200’ higher than they are today! Modern Lake Erie is a smaller remnant of that former lake. Several beach ridges elevated above the surrounding land provide clues about former lake levels under changing conditions that followed the Ice Age. Early in the settlement of this area, these sandy ridges provided important transportation corridors through the vast swampy terrain, where the fine sediments typical of deposition in a lake environment led to poor drainage and standing water. Many of these areas have subsequently been artificially drained. The flat terrain provided for some easy pedaling, without many hills to climb over!