The Effects of Grazing by Snow Geese on Coastal Salt Marshes

The influence of grazing by the Snow Goose (Anser caerulescens subspecies atlantica) was studied in three distinctly different North Carolina salt marshes. One marsh was dominated by Spartina alterniflora, one by a mixture of Spartina patens and Distichlis spicata, and one by Scirpus robustus. Snow Goose grazing consists principally of removal of roots and rhizomes to a depth of 20—25 cm. Exclosures were utilized to compare (1) belowground biomass and net production, (2) aerial plant cover and (3) detritus availability between grazed and ungrazed plots. Ungrazed portions of all study had significantly more biomass (P <.001) than grazed areas in the year following grazing. Belowground net production was less in the grazed portions of two of the sites (P < .10). Grazing intensity, measured as percent biomass removed, was 58.1 ± 7.4% at all sites. Plant cover was reduced at all sites in the spring following grazing. The Scirpus robutus marsh recovered more rapidly than the other marshes and appears to be a more stable grazing system. Finally, at South Pond and Salt Flats, more uprooted root—rhizome material was found in grazed areas than in ungrazed (P < .001, P < .05 respectively). This strongly suggests that Snow Geese make belowground net production available for transport to nearby estuarine waters where it could be used by estuarine consumers.