Tipping the tipping point: After a regime shift to Typha dominance can management push the system back to a pre-invaded state?

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Jason P. Martina , Kenneth J. Elgersma , Deborah E. Goldberg , Sean J. Sharp, William S. Currie

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Typha x glauca dominance in Great Lakes wetlands is strongly influenced by nitrogen (N) loading and is managed with varying degrees of long-term success, in part due to persistent eutrophication. However, even if N loading decreased, invasion might persist if a regime shift, reinforced by high internal N cycling, maintains invader dominance. We used MONDRIAN, a wetland community-ecosystem model, to explore the dynamics of Typha invasion into a 3-species native community across a range of N loading scenarios. These included either constant or decreasing N loading where the system starts in a high-N state and ends in a low-N state across a 65-year time period. Management was implemented 15 years post N reduction to determine if herbiciding /burning could return the system back to a pre-invaded state. In the constant N loading scenarios, an invasion threshold was observed between 8 and 12 g N m-2 yr-1 , in which the invader proportion went from less than 20% to greater than 80%. Typha dominance continued after dramatic N reduction, resulting in a 79% regime shift for invader proportion and 31% regime shift for total community NPP. While management was not able to fully return the system to a pre-invaded state, six years of management was found to be partially successful, leading to a 38% reduction in invader NPP and 31% reduction in invader proportion compared to pre-treatment, post-regime shift levels. These results suggest that in historically eutrophic wetlands, management can partially help return the system to a pre-invaded state after high N loading is removed.

Resource Type:
Conference Presentation, SER2021

Pre-approved for CECs under SER's CERP program