Collapse of an arctic bird community resulting from ungulate-induced loss of erect shrubs

Abstract

Rapid, but contrasting, changes in the extent of erect thicket-forming shrubs is presently seen in the Arctic, either resulting from a warmer climate (increasing extent) or intensified herbivory (decreasing extent). We investigated the impact of loss of willow shrubs on a bird community in arctic riparian sediment plains in northern Norway subject to varying intensities of reindeer browsing. In riparian habitats where willow thickets had been lost, bird species richness was more than halved compared to habitats where some patches of thickets were still present. As could be expected species previously suggested to use erect woody vegetation as nesting places and/or foraging habitats were most consistently impacted. However, even some open ground habitat specialists appeared to be negatively impacted, possibly due to loss of spatial spill-over effects of insects from willow thickets. To preserve low-arctic avian biodiversity in a warming climate, management should strive to identify levels of ungulate browsing that strike the balance between shrub-encroached and shrub-denuded arctic tundra.

Bird Communities of the Arctic Shrub Tundra of Yamal: Habitat Specialists and Generalists

“…Intense grazing by reindeer/caribou ( Rangifer tarandus ) can, however, limit shrub expansion [20], and may even lead to a decrease of willow shrub cover when densities are particularly high [21], [22], [23]. Grazing induced loss of shrubs has been shown to strongly reduce bird species richness in northern Norway [24]. In addition, increased human activity in tundra areas related notably to oil/gas exploitation leads to increased disturbance, habitat fragmentation and erosion of some key tundra habitats [25].…”

“…How these habitat changes affect the different components of tundra ecosystems is however still unclear [23]. Understanding bird habitat associations will improve our understanding of the likely impacts of different components of global change on these communities, but these associations and their spatio-temporal variation are as far as we know very poorly known, with only a handful of studies done in the low Arctic [24], [26], [27].…”

“…thickets for the bird communities, as their extent in the shrub tundra is likely to change under the influence of climate change, erosion and/or intense browsing. Willow thickets have been described as hotspots of productivity and biodiversity in general [23], [24], [35], [36], with a positive effect on bird species richness in particular [24], [35]. Higher bird densities and higher species richness would thus be expected in this habitat.…”

The Response of Alpine Salix Shrubs to Long-Term Browsing Varies with Elevation and Herbivore Density

“…form an important constituent of Alpine and arctic vegetation, with large influences on ecosystem and community dynamics (Eldridge et al, 2011;Ims and Henden, 2012). Salix shrubs provide important forage and habitat for many taxa using alpine areas, including the characteristic and economically important reindeer (Rangifer tarandus) and grouse species (Lagopus spp.)…”

Ecology and economics of reindeer herding systems

“…Lichens especially are an important energy resource for reindeer during winter. However, reindeer numbers are high in many districts, which may lead to overgrazing of lichen pastures (Mysterud 2006) and decreases in bird species richness and biodiversity (Ims and Henden 2012). Large herd sizes are the main reason for the reduction in lichen biomass, but forestry, mining, and other land uses also affect the situation (Kumpula et al 2014).…”