Black ash wetlands are widespread, forested landscape features in the western Great Lakes region. Despite the prevalence of these ecosystems, their future is threatened due to impending spread of the invasive emerald ash borer (EAB). These invasions result in tree mortality, decreased transpiration, and potential shifts to wetter, non‐forested conditions. The susceptibility to such ecohydrologic shifts likely varies according to local hydrologic regimes controlled by landscape settings, but this site‐dependent vulnerability is not well understood and thus scientists have no reliable metchanism for predicting it. As a result, developing adaptation strategies to contend with emerald ash borer invasions is extremely difficult.
In a new study published by Hydrological Processes, NE CASC PI Anthony D'Amato and his collaborators assess potential vulnerability as a function of site hydrology in 15 undisturbed black ash wetlands from their three most common hydrogeomorphic settings in northern Minnesota: lowland, depression, and transition. The team also uses high‐resolution (1‐cm) surface elevation models to assess spatial variability of water levels at a subset of 10 sites. Their results indicate that lowland sites are generally drier because of elevated landscape position and greater water level drawdowns.
Based on this finding, they predict that such drier sites will exhibit greater water level increases following EAB‐induced ash mortality, compared to wetter sites where open water evaporation and shallow‐rooted understory transpiration will offset losses in tree transpiration. Moreover, compared to wetter sites, drier sites exhibit minimal microtopographic variation, limiting the number of elevated microsites for tree establishment and eventual canopy recovery after ash loss.
These results suggest that site wetness is a simple and effective predictor of black ash wetland vulnerability to hydrologic regime change. To that end, D'Amato and his collaborators also assess the ability of common terrain metrics to predict site wetness, providing a potential tool to target vulnerable areas for active management efforts.