Great Lakes alkaline rockshore is a community that develops on creviced, wave-splashed, horizontal or gently sloping exposures of dolomite bedrock that dip toward Lake Michigan. These occur only along the Lake Michigan shoreline of the northern Door Peninsula, and on the margins of some of the Grand Traverse Islands to the north. This is the same bedrock that forms the Niagara Escarpment, which forms prominent cliffs on the west side of the Peninsula. The extent of the exposed rock is dependent on Lake Michigan water levels and large expanses of this habitat may be either inundated or exposed during a given year. Characteristic flora of this community includes shrubs ninebark (Physocarpus opulifolius) and shrubby cinquefoil (Dasiphora fruticosa), and herbs silverweed (Potentilla anserina), birds-eye primrose (Primula mistassinica), grass-leaved goldenrod (Euthamia graminifolia), brook lobelia (Lobelia kalmii), gentians (Gentiana spp., Gentianopsis spp.), grasses-of-Parnassus (Parnassia spp.), Indian paint-brush (Castilleja coccinea), low calamint (Clinopodium arkansanum), and many sedges and rushes. Plants endemic to the Great Lakes shores are significant components in some stands.
Because this community type is geographically restricted to those portions of the Lake Michigan coast with dolomite shoreline, it is, and has always been, rare here. There is often a narrow zone of rank herbs and tall shrubs just inland of the exposed dolomite pavement, sometimes occupying a ridge of cobbles, gravel, or a low ledge. On the more stable habitats beyond this zone of herbs and shrubs, a very distinctive forest sometimes develops. Mature stands are usually composed of mixtures of northern white-cedar (Thuja occidentalis), white spruce (Picea glauca), balsam fir (Abies balsamea), eastern white pine (Pinus strobus), and paper birch (Betula papyrifera).
