PARENT SESSION
Oral Session # 65: Herbivory V: Deer, Geese, and Chemistry.
Presiding: K Bjorndal
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Contrasting nutrient limitations in arctic coastal marshes: Implications for goose foraging.
Ngai, Jackie*,1, Jefferies, Robert1, 1 University of Toronto, Toronto, Ontario, Canada
ABSTRACT- Marshes grazed by snow geese on the Hudson Bay coast were examined to determine whether a switch from nitrogen- to phosphorus-limited plant growth occurs between the salt marshes and adjacent freshwater marshes. Experimental plots, which were fertilized with N and P in a factorial design, were set up in both a salt and freshwater marsh, and plant biomass and tissue nutrient content responses to the fertilization treatments were measured. In the salt marsh, it was found that, when added alone, N and P had non-significant effects on aboveground biomass. However, there was a significant increase in biomass when the nutrients were added together, with nitrogen being the most important element determining the response. In contrast, in the freshwater marsh, the addition of N did not significantly increase aboveground biomass, although there was a significant effect of P additions. No NP interaction was observed in the freshwater site, while in the salt marsh, P does become limiting when N availability is supplemented. N:P stoichiometry also indicates that plant growth in the salt marsh is mainly N-limited, while that in the freshwater marsh is P-limited. In recent decades, destructive feeding by geese has destroyed much of the salt marsh, and the geese have been forced to forage in the freshwater site. This difference in nutrient limitation between the salt and freshwater marshes means that vegetation available for geese during the post-hatch period is now P- rather than N-limited. The potential implications of this change in forage quality will be assessed in terms of the observed decline in gosling growth.
Key words: geese, nutrient limitation, N:P ratio, plant growth