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System: Palustrine
Subsystem: Shrubland
PA Ecological Group(s): Great Lakes Region Wetland

Global Rank: GNR rank interpretation
State Rank: S1

In Pennsylvania, this community type occurs only on Presque Isle, on the shore of Lake Erie. It is found as a zone surrounding swale ponds, slightly higher in elevation than the ponds but lower than the dune ridges. The substrate is sand, and the water table fluctuates seasonally; it is at or near the surface during the spring, and by autumn it falls below the surface but remains accessible to deep-rooted shrubs. The community is dominated by a mixture of bayberry (Myrica pensylvanica), silky dogwood (Cornus amomum), red-osier dogwood (Cornus sericea), Morrow's honeysuckle (Lonicera morrowii), and willows (Salix spp.), with scattered eastern cottonwood (Populus deltoides) and European white birch (Betula pendula). Herbaceous species include bluejoint (Calamagrostis canadensis), sedge (Carex scoparia), Bebb’s sedge (Carex bebbii), blackish wool-grass (Scirpus atrocinctus), Canada goldenrod (Solidago canadensis), sharp-fruited rush (Juncus acuminatus), and southern blue flag (Iris virginica). The community tolerates fluctuation of water levels within a season, due to weather fronts or seasonal variation in precipitation; fluctuations in lake levels over decades may move the community around on the landscape or eliminate it during some years.

This community type is part of the "Great Lakes Region Beach – Dune – Sandplain Complex" (Fike 1999). This complex occurs on a substrate of glacial sand and gravel deposits. This material is constantly being eroded and redeposited by the action of currents, waves, and storm events. The dynamic nature of the substrate maintains a variety of successional stages. Additionally, the porous nature of the substrate causes the water table to respond quickly to changes in lake level. As a result, natural communities occur as a complicated mosaic of different hydrologic conditions, seral stages, physiognomies, and floristic assemblages that shift over time. Great Lakes Region Bayberry – Mixed Shrub Palustrine Shrubland is successional, and may transition to woodland or forest if it does not experience major disturbances.

Critically imperiled in the jurisdiction because of extreme rarity or because of some factor(s) such as very steep declines making it especially vulnerable to extirpation.

*Vascular plant nomenclature follows Rhoads and Block (2007). Bryophyte nomenclature follows Crum and Anderson (1981).

This community is only found along the shores of the Great Lakes. Pennsylvania has a limited extent of shoreline along Lake Erie, and the only remaining examples of this community in Pennsylvania are found at Presque Isle State Park. The lake shore habitat, with its sandy substrate and fluctuating water levels, hosts a substantially different flora and fauna than other Pennsylvania habitats. Because there are no other examples of this habitat within Pennsylvania, there are 77 state rare, threatened, or endangered plant species in Presque Isle communities (Beach 2007). While many plant species found here are common in Ohio, Michigan , and other Midwestern states, some species are specifically adapted to the freshwater shoreline conditions of the Great Lakes and cannot live anywhere else. The lake shore complex also hosts a unique suite of invertebrates such as tiger beetles, spiders, and sand wasps. It is an important refuge for migrating waterbirds and shorebirds. Presque Isle is also used by migrating passerine bird species, which cross the lake at the narrow point between Presque Isle and Long Point on the north shore.

The invasive exotic species Morrow’s honeysuckle (Lonicera morrowii) is a major threat to the Great Lakes Region Bayberry – Mixed Shrub Palustrine Shrubland. Presque Isle State Park is heavily used for recreation; in some areas overuse damages plant communities.

The addition of engineered structures to the shoreline, such as breakwaters and jetties, has altered the natural erosion and deposition processes that develop the lake shoreline. Shoreline development is part of the long-term physical process that creates the palustrine shrubland habitat behind the leading dune.