Assessing the Waterfowl Forage Value of Wetland Plant Communities

Abstract

Invasive Phragmites australis continues to threaten wetland biodiversity and reduce food availability for waterfowl across North America. Assessing how vegetation responds to suppression efforts, and how these changes influence forage quality, is essential for informing management. In this study, I adapted the Vegetation Forage Quality Index (vFQI) for use in southern Ontario by developing updated forage value coefficients through expert elicitation. I also introduced a new tool, the Weighted Mean Waterfowl-forage Coefficient (WMWCs), modified to reduce the influence of species richness on the index score. I tested both indices in wetlands of the Long Point and Big Creek National Wildlife Areas, where P. australis suppression was conducted to evaluate the impact of suppression on waterfowl forage value. Field surveys (2022-2023) revealed that the WMWCs, but not the vFQI, successfully distinguished among invaded, treated, and reference sites, detecting improved forage quality in treated areas two years post-treatment. However, neither index was strongly correlated with empirical seed mass data from sediment cores, suggesting that seed biomass alone may not fully reflect foraging value. This study highlights the limitations of richness-sensitive indices like the vFQI and demonstrates the potential of WMWCs as a more robust indicator of wetland forage quality for waterfowl. Recommendations for future work include validation with bird observations and long-term monitoring to better capture temporal recovery dynamics.