The Great Lakes beach community occurs at the interface of land and water along the margins of Lakes Michigan and Superior, often in association with sparsely vegetated, semi-stabilized dune systems. Great Lakes beaches are extremely dynamic features, strongly influenced by water level changes and storm events. The lower beach is continually impacted by waves, the middle beach supports a dynamic plant community affected by wave action only during storms, and the upper beach, affected by wind-blown sand, wave spray, and only the most severe storms, supports a relatively diverse assemblage of plants.
The beach flora is typically sparse due to the scouring action of waves and ice. However, following several years of low water with few major storm events, the vegetation of the upper beach zone can become quite dense. Floristic composition can be an odd mix that includes globally rare endemics, as well as widespread weedy species adapted to quickly colonizing disturbed areas swept bare of competing vegetation. Exposed shorelines may be entirely unvegetated. Plants endemic to the shores of the Great Lakes, such as seaside spurge (Euphorbia polygonifolia) and American sea-rocket (Cakile edentula), are characteristic of some of the Lake Michigan beaches, especially during low water periods. Native associates may include silverweed (Potentilla anserina), Baltic rush (Juncus balticus), and water horehound (Lycopus americanus). The beaches on Lake Superior are for the most part unvegetated but are important foraging, resting, and breeding areas for both migrating and resident birds.
