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Wildside column: Waves on the Big Lake make unique habitats

Purple pitcher plants growing in the Julian Bay sphagnum bog, Stockton Island in the Apostle Islands National Lakeshore. Pitcher plants are carnivorous, capturing insects in their pitcher-shaped leaves to obtain nutrients. Photo courtesy of Dan Wilcox

Although we have all the Apostle Islands on our "bucket list" to visit, we often return to Stockton Island. Last week Wednesday our boat got a workout powering into stiff northeast wind and waves. The "Lake is the Boss" T-shirt logo applies when the wind is from the north and east. There aren't many safe overnight anchorages in the Apostle Islands when the wind is from those directions. Presque Isle Bay on Stockton Island provides fine shelter from the north and east winds.

Stockton Island is one of the most popular of the Apostle Islands National Lakeshore, with good anchorages and fine beaches at Quarry Bay, Presque Isle Bay and Julian Bay, a constructed harbor, campsites and a visitor center at Presque Isle Bay, and miles of hiking trails. Like the other Apostle Islands, Stockton Island has a fascinating geology and unique habitats shaped by the big lake.

The bedrock sandstones of the Apostle Islands were deposited during the lake Precambrian era about one billion years ago. The upper and lower layers, Chequamegon and Orienta formations, were deposited by braided streams flowing to the northeast. The Devils Island formation between the sandstones, was deposited in sand flats intermittently covered by shallow water.

During the Pleistocene era, glacial ice advances left till and outwash deposits that cover the islands. Higher water levels of Lake Superior left terraces, wave-cut benches and beaches on the islands. Following the last glaciation about 12,000 years ago, Glacial Lake Duluth submerged most of the islands and the Bayfield Peninsula. Land rebound and lower lake levels left the Apostle Islands separated from the mainland.

Relentless pounding by wave action eroded sandstone on the islands into sea caves. Waves eroded high bluffs and glacial drift to form sand spits and bay-mouth bars. This geologic history and the Lake Superior weather have resulted in regionally rare habitats including old growth forests, clay bluff, sandstone, lagoon, bog and dune communities. The Wisconsin DNR National Heritage Inventory Program has designated Maritime Forest, Sandscape (including beaches, sandspits, cuspate forelands and tombolos) and Maritime Cliff State Natural Areas within the Apostle Islands National Lakeshore.

Waves washing onto a beach at an angle lift and carry sand along the shore. This "littoral drift" of sand forms sand spits and cuspate forelands. On Stockton Island are two tombolos, land formed by sediment from Presque Isle and Julian Bays, connecting Stockton Island to Presque Isle, once a separate island.

Newly deposited sand is a harsh environment. Plants there are adapted to survive under severe shifting sand, wind and low nutrients. Pioneering American beach grass and beach pea trap sand and stabilize the dunes. Microorganisms fix atmospheric nitrogen providing conditions where other species of plants and animals can live. Beach heather, dwarf juniper, blueberry and wild rose help further stabilize the dunes. White pines, red maple, speckled alder and white birch grow on the older dunes.

Behind the dunes and bay-mouth bars are lagoons and bogs. Protected from wave action of the big lake, the lagoons have submersed, emergent and floating aquatic vegetation like pondweeds, rushes, sedges and watershield. The bogs have sphagnum moss, leatherleaf shrubs, pitcher plants and sundew, all adapted to growing in wet low nutrient conditions.

You can get to Stockton Island on a seaworthy boat. Sea kayak rentals, guide services, a tour boat and water taxi rides to the island are available at Bayfield on the mainland. A National Park Service naturalist at the visitor center on the island gives evening campfire talks. Stockton is a great place to hike around to see the variety of habitats shaped by the big lake. The island also supports one of the highest concentrations of black bears in North America so keep an eye out when picking blueberries there.

Please send any comments and suggestions for this column to me at news@rivertowns.net .

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