Different mechanisms of goose influence both accelerate and retard the decomposition process in an Arctic wetland

Background and aims Due to human induced changes in their wintering grounds, goose numbers increased dramatically over the past 50 years. To understand the consequences of these changes, studies on key ecosystem processes, like decomposition, on the breeding grounds in the generally severely nutrient limited Arctic are indispensable. This article reports on the influence of Barnacle Geese Branta leucopsis on the decomposition process and the release of nitrogen from litter on high-Arctic Svalbard (78° 55' N, 11° 56' E).Methods The study made use of paired long-term exclosures and control plots. Litter and goose droppings were collected and subsequently analysed on chemical parameters to understand the influence of grazing via a change in dead organic matter quality within and between plant growth forms and faeces. Reciprocal transplantation of dead organic matter (graminoids, mosses, roots and faeces) between ungrazed (exclosures) and heavily grazed areas, using the litterbag technique, was used to study the goose grazing influence on litter decomposition and nitrogen release through a shift in environmental conditions. The possibly facilitating role of goose faeces was investigated by studying decomposition in separate subplots with faeces addition in some of the exclosures.Results In the exclosures almost twice the necromass of grazed plots was present and the contribution of litter originating from graminoids and roots was respectively twice and four times as much in the exclosures compared to the grazed plots. This is important seen the fact that these growth forms were found to differ in litter quality. Together with the place of production and thus incubation, this resulted in a decrease in decomposition and nitrogen release rates in the following order: roots, graminoids and moss. Goose-induced changes in litter composition thus impeded decomposition. Environmental impact of geese, in contrast, was found to enhance decomposition, but not nitrogen release rates of the same litter type. Goose faeces, characterised by a distinct chemical quality, were found to decompose as slow as moss litter and release nitrogen as fast as graminoid litter