Forage variation in brood-rearing areas used by pacific black brant geese on the Yukon-Kuskokwim delta, Alaska

Abstract

1 We investigated the effects of grazing by black brant geese on Carex subspathacea lawns on the Yukon-Kuskokwim delta, Alaska. 2 We compared variation in growth and forage quality in both grazed and temporarily exclosed sites to determine responses of C. subspathacea to grazing at landscape scales within two nesting colonies that had experienced different population dynamics over recent decades. 3 Landscapes differed in forage quality, grazing patterns, and in the effect grazing had on C. subspathacea forage characteristics. We found no effect of grazing on net above-ground primary productivity (NAPP) over a wide range of natural grazing intensities at the landscape scale. 4 No differences in forage quality, NAPP, or response of C. subspathacea growth rates to grazing pressures could be detected between colonies. This suggests that goose grazing does not have deleterious effects on C. subspathacea in this ecosystem. 5 It has been suggested that gosling growth rates are sensitive to seasonal declines in forage availability and quality. Spatial variation in forage quality and availability per sampled area exceeded seasonal variation in these characteristics and is likely to have dramatic effects on gosling growth and recruitment rates.