Grazing by captive Barnacle geese affects graminoid growth and productivity on Svalbard

Migratory geese breed in Svalbard in summer and return to Western Europe for the winter, feeding on wetlands and agricultural fields. Recent changes in climate, land use and the implementation of protective measures dramatically improved the birds\u27 ability to survive the winter, increasing population sizes and thus the potential grazing impact on Svalbard. This study measured live leaf length and aboveground productivity of Alopecurus borealis and Dupontia fisheri, widespread forage grasses on Svalbard, in order to make a quantitative assessment of the short term effects of different intensities of goose grazing. In addition we wanted to establish whether warming could enhance graminoid growth and regenerative capacity of grazed grasses. We carried out a factorial experiment of grazing (control, normal and high grazing pressure) using captive wild barnacle geese and temperature manipulation using open top chambers (OTCs) in a mesic and wet habitat in Adventdalen, Svalbard (78°N , 16°E ), following the growth of individual tillers before grazing and up until 20 days after grazing. OTCs enhanced temperatures and growth rates for Alopecurus in the mesic habitat, but slightly decreased belowground temperatures and early season growth for Dupontia in the wet habitat. Grazing stimulated growth rates resulting in increased cumulative leaf length production. The strength of response was greater for Alopecurus than Dupontia. We suggest that nutrients released by goose faeces were taken up by Alopecurus thus enhancing their growth rates, but that the thick layer of mosses prevented the addition of faeces from benefitting Dupontia as much