This site extends along nearly 28 miles of the St. Croix River beginning at the cities of St. Croix Falls, Wisconsin, and Taylors Falls, Minnesota, and extending south to Stillwater, Minnesota. The upper part of this site is characterized by a dramatic gorge that was cut through the basalt ?trap rock? by waters draining from Glacial Lake Duluth (Dunn 1979: pp. 8-9), while the lower stretch is underlain by limestone. The river channel here was cut by waters draining from Glacial Lake Grantsburg. Vegetation on the rocky gorge is relatively sparse and dry. Numerous exposures of rounded rock, cliffs, and boulders are barren, while similar sites with greater moisture are home to numerous ferns, mosses, and lichens. Dry forest containing red cedar, basswood, white pine, and bur, white, and black oaks occurs throughout the site (WDNR 2007a). The lower section of this site contains excellent examples of floodplain forest, emergent aquatics, forested seeps, and running sloughs and backwaters of the St. Croix River. Silver maple is the dominant canopy species in the floodplain forest, along with green ash, hackberry, and American elm. Basswood, red oak, cottonwood, black willow, and bitternut hickory also are present in smaller numbers. The surrounding upland forest contains oak, basswood, big-tooth aspen, paper birch and an occasional white pine. Scattered patches of dry prairie and savanna vegetation can be found on the warmer western and southern exposures. Rough, deeply dissected terrain borders the lower St. Croix River with a local relief exceeding 350 feet. Banks at the base of the river terrace often contain seepages that harbor large populations of the state-endangered bog bluegrass. Shallow water areas contain abundant bulrush, rice cut grass and prairie cord grass (WDNR 2007b).
This IBA provides critical habitat for various high conservation priority species, particularly those associated with floodplain forests. Red-shouldered Hawk, Eastern Wood-Pewee, Yellow-throated Vireo, Cerulean Warbler, Prothonotary Warbler, and Louisiana Waterthrush all breed here. The bluffs provide ideal nesting for Bank, Cliff, and Northern Rough-winged swallows. Bald Eagles, Hooded Mergansers, and Belted Kingfishers breed along the river corridor or in backwater areas, and marsh habitats support American Bittern and Marsh Wren. There are several large Great Blue Heron rookeries along this portion of the river, and Bald Eagles can be common in winter if enough areas of open water remain (Maercklein 2005b).
This site encompasses numerous public and private parcels that are managed for conservation, wildlife habitat, and recreation. These include the lands along the St. Croix National Scenic Riverway, Interstate State Park, Osceola Bedrock Glades State Natural Area, Farmington Bottoms State Natural Area, parcels owned by Standing Cedars Conservancy, and St. Croix Islands State Wildlife Area. The importance of this site is recognized on both sides of the river corridor, and this IBA mirrors the Middle St. Croix River IBA established on the Minnesota side. This site faces a variety of conservation challenges. Pressure is increasing for residential development, which can fragment habitat. Cell towers, wind turbines, and power lines, all of which can cause avian mortality, are proposed along the river bluffs nearly every year. Sediments, excess nutrients, and pesticides from construction, gravel pits, agricultural lands, and residential lawns can impact water quality. Native habitats are susceptible to invasive plants such as common buckthorn, prickly-ash, garlic mustard, purple loosestrife, Grecian foxglove, nodding thistle, and others. Prairie and savanna areas have been degraded by woody encroachment. Recreational use of the river may create disturbance for birds, particularly nesting Bald Eagles and Great Blue Herons. Standing Cedars Conservancy is actively restoring oak savanna and controlling invasives through brushing and prescribed fire. Fire may also be adopted by the National Park Service for prairie management. Purple loosestrife infestations are targeted for removal every year and dense patches are treated with loosestrife beetles.