Lake Superior coastal habitats are adapted to seasonal and annual water level fluctuations, but the response of vegetation to changes in the frequency and duration of low or high water levels is uncertain. To meet the challenge of detecting directional or cyclic changes and their causes in naturally dynamic ecosystems, we monitor. My research focuses on the response of coastal vegetation to re-wetting after the longest period of drought and lowest water depths recorded for Lake Superior. To address this, I use pre-drought, mid-drought, and post-drought data from coastal wetland communities on the south shore (Apostle Islands National Lakeshore) and rock pool and splash zone communities with rare Arctic disjunct species on the north shore (Isle Royale National Park).
Results/Conclusions
The plant communities in coastal estuaries and interdunal wetlands with Sphagnum peat mats (poor fens) were less responsive to water level changes than were coastal emergent marshes, sedge meadows, and sand pannes. Wetlands without a Sphagnum component gained shrub species and lost obligate wetland plant species during the prolonged low water years. Wetlands that had saturated or dry soils during the drought years now have >0.5m of standing water due to higher than average water levels. Shrubs that encroached during drought years are stressed or dead and obligate wetland plants have returned in a cyclic pattern that reflects pulse stability processes that maintain these communities in the long-term. North Shore bedrock communities have similarly demonstrated variability in population dynamics related to extreme Lake Superior water level fluctuations. Several rare plant species declined during the prolonged drought period. Post-drought, some species display high or sustained local abundance post-drought. By synthesizing trends in plant responses to extreme water level change across multiple coastal habitats, we broaden our understanding of the signature of water level influence on Lake Superior’s diverse coastal communities. Continued monitoring is necessary to study the response of these populations to increasing winds and heavy storm events that are occurring in the Great Lakes region.