Effects of foraging by pink-footed geese on tundra vegetation in Svalbard: an assessment of extent and a proposal for a monitoring program

Increasing population sizes of some herbivorous Arctic breeding species have caused extensive damage to tundra vegetation, whose resilience to intensive herbivory is low, with very slow rates of plant recovery. Here we assess the impacts of the feeding activities of a rapidly growing population of pink-footed geese Anser brachyrhynchus on the Svalbard tundra at both spring pre-breeding staging sites and summer nesting grounds over a seven year period in four different sites in Isfjorden. From 2006 to 2013 the population of Svalbard pink-footed geese increased from 52,000 to 81,500 individuals. Over the same period there was an increase in goose use of less favoured, but much more abundant, drier habitat at the expense of less abundant but preferred wetter tundra at pre-breeding staging sites. Spring snowmelt occurs first in drier areas with prolonged snow cover in wetter parts and we observed a positive correlation between the extent of spring snow cover and use of drier habitats. Hence, both an increasing population size and late spring snowmelt are likely to lead to extensive use of drier habitats. Drier areas are less resilient to disturbance and take longer to recover from damage than wetter habitats, thus it is now likely that pink-footed geese are causing long-term vegetation changes at pre-breeding sites. Pink-footed goose foraging choices appear somewhat different at their nesting grounds. Here, they fed in previously disturbed wet habitat in close proximity to their nests. Presumably this allowed them to quickly return to the nest if predators were spotted, while also feeding in locations where the rooting structures of forage plants have been disturbed, making extraction from the soil easier. Long-term damage to tundra vegetation therefore seems more likely to occur at pre-breeding sites where habitat availability can be restricted by snow cover and an increasing population size.
Based on our sampling protocol and transect design, we propose an adaptive monitoring program which incorporates gradients in wetness of habitats and snow cover in four sites in Isfjorden. Ideally the monitoring should be carried out at 3-year intervals to be coordinated with the reporting from the AEWA international adaptive management plan for the Svalbard population of the pink-footed goose.