Geese Turn Marshes Into Barren Ground
Lesser snow geese have stripped the coastal marshes of Hudson Bay bare of vegetation and researchers say it will be decades before plants grow there again.
Along the small portion of marine shoreline studied in Ontario, Manitoba and Nunavut, 35,000 hectares of tidal marsh have lost vegetation to the geese since the mid-1970s.
During those years, the mid-continent group of lesser snow geese that winters along the Gulf of Mexico has enjoyed a population explosion, increasing by 5 to 7 percent annually. By 1997, with over 5 million adults, they had become the most numerous goose species breeding in the Canadian Arctic.
The snow geese stage and nest in large gatherings along the western Hudson Bay coast as soon as the ground thaws. There they destructively grub for roots and rhizomes of salt marsh grass and sedge. When those areas become depleted, they move into nearby freshwater wetlands, where they pull out entire sedge and grass shoots. The plants cannot recover from the repeated assaults so the sites convert to exposed ground.
The changes wrought by the geese reverberate through to the sediment. Once exposed, the soil in salt marshes becomes too saline, compacted and depleted of nutrients to support plant life. There are no signs of an ecosystem recovering at tidal marshes that have reached this damaged a state. Since freshwater marshes are not affected by salt, they can regrow plants within a decade.
The number of geese using each nesting or resting site has varied over the years and so too the rate that bare ground spreads. As the marshes at one location become degraded, it is abandoned and breeding colonies move into new areas. For southern Hudson Bay, the process of goose-induced obliteration and eventual revegetation means a marsh can accommodate large populations of snow geese on a 60 to 100 year boom-and-bust cycle.
Robert L. Jefferies, Andrew Jano and Kenneth Abraham. 2006. A biotic agent promotes large-scale catastrophic change in the coastal marshes of Hudson Bay. Journal of Ecology. 94(1): 234-242.