Foraging geese, vegetation loss and soil degradation in an Arctic salt marsh

Abstract. The North American mid-continent population of Lesser snow geese (Chen caerulescens caerulescens L.) has increased by ca. 7% per year, largely as a result of geese feeding on agricultural crops in winter and on migration. We describe the long-term effects of increasing numbers of geese at an arctic breeding ground (La Pérouse Bay, Manitoba) on intertidal salt-marsh vegetation. Between 1985 and 1999 goose grubbing caused considerable loss of graminoid vegetation along transects in intertidal marshes. Loss of vegetation led to bare sediment with a plant cover of less than 2%. Changes in vegetation could not be described by simple linear, geometric or exponential functions; most losses occurred between 1988 and 1990 and losses were staggered in time between individual transects, some of which had all vegetation removed.

Between 1979 and 1999 the standing crop in July in remaining intact heavily-grazed swards of Puccinellia phry-ganodes and Carex subspathacea fell from 40–60 g m^-2 to 20–30 g m^-2. Intense grazing on remaining patches of sward has restricted growth of these clonal forage plants and hypersalinity of bare sediments has precluded re-establishment of vegetation. Between 1989 and 1993 numbers of faecal droppings in grazed plots reached maximum values of 15–22 droppings m^-2 wk^-1. Since then peak values have remained at less than 13 droppings m^-2 wk^-1. The loss of vegetation and changes in soil conditions have resulted in the establishment of an alternative stable state (hypersaline bare sediment).