Herbivore impact on moss depth, soil temperature and arctic plant growth

We provide evidence for a mechanism by which herbivores may influence plant abundance in arctic ecosystems, These systems are commonly dominated by mo sses, the thickness of which influences the amount of heat reaching the soi l surface. Herbivores can reduce the thickness of the moss layer by means o f trampling and consumption. Exclusion of grazing by barnacle geese and rei ndeer over a period of 7 years at Ny-Alesund, Spitsbergen, caused an increa se in the thickness of the moss layer, and a reduction in soil temperature of 0.9 degreesC. Soil temperature was negatively correlated with moss-layer thickness across sites, with highest soil temperatures where moss layers w ere shallow. We found that moss growth did not respond to experimental mani pulation of soil temperature, but the grass Poa arctica (arctic meadow-gras s) and the dicot Cardamine nymanii (polar cress) suffered a 50% reduction i n biomass when growing in chilled soils.