PARENT SESSION
Symposium 6: Anthropogenic Modification of North American Salt Marshes: Causes, Consequences and Recommendations
Organized by: B Silliman
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Chatham Ballroom C.

Herbivores as opportunists: migratory connectivity and large scale disturbance in Arctic coastal ecosystems.

Henry, Hugh^*,1, ¹ Department of Botany, Toronto, Ontario, Canada

ABSTRACT- In recent decades, migratory geese that breed in the Arctic, but overwinter in temperate regions of Northwestern Europe and North America, have shown dramatic increases in numbers that appear to be linked to their increasing use of agricultural crops as a food resource. The foraging behaviour of the mid-continent population of lesser snow geese is an example of this change in resource acquisition that has led to a relaxation of the density-dependent regulation which occurred earlier in their traditional wintering area, the coastal marshes of the Gulf States. The agricultural nutrient subsidy has led to strong top-down effects in the coastal marshes of the Hudson Bay Lowlands and at other locations where the increased numbers of birds breed - a consequence of migratory connectivity. Direct and indirect biotic and abiotic processes mediated by feedback mechanisms and initiated by goose foraging have led to sustained change resulting in the development of alternative stable states. These non-linear changes, that display threshold responses, include loss of vegetation, irreversible changes in soil properties and a decline in microbial activity, and decreases in invertebrate and passerine species. The coastal systems display low resilience, and the coalesence of local disturbed areas has led to a highly fragmented landscape where there is a marked temporal asymmetry between a possible decline in goose numbers and revegetation of coastal areas. The effects of increased numbers of geese on nitrogen dynamics in particular may alter drastically the productivity and stability of these systems. In a model of the flows of nitrogen of a grazed lawn in an Arctic coastal marsh, the alternative stable states of the system are obtained with values for the state variables that are consistent with field data. The determining factor in the transition to an alternative stable state is the loss of the input of nitrogen from fixation when lawn area is reduced by geese.

Key words: lesser snow goose, disturbance, Arctic salt marsh, migratory connectivity