Understanding the role of rodents as regulators of scrub cover in tundra landscapes,and how their grazing impacts vary in time and space,will help mitigate the consequences of Arctic greening.Previous research has yielded contrasting results about the relative strength of rodent-plant interactions in the Arctic,probably due to spatial differences in the extent to which terrestrial arctic predators are subsidized by allochthonous resources.Here,we evaluated the potential for marine subsidies to predators to trigger top-down controls of terrestrial tundra trophic webs on Fennoscandian tundra.We present a detailed evaluation of predator-rodent-vegetation interactions along a coast-inland gradient,during the 2011 rodent outbreak and the two following decline years,by using direct assessments of rodent impacts and tracing of marine-derived nutrients to the food web.Despite the large contribution of rodents in the diet of avian predators,the fraction of the rodent populations taken daily by birds remained far below both the observed and estimated maximal daily growth rates of rodent populations,regardless of the distance to the sea.Our findings also point to pronounced damages caused by small rodents to vascular plants,especially dwarf shrubs,in both coastal and inland areas.Taken together,our results indicate that the combined predation rate of all predators was not sufficient to suppress the summer growth rate of rodent populations during the snow-free period and prevent large-scale grazing impacts.Instead,they suggest that the contrasting predator-rodent-vegetation interactions among arctic regions may emerge from a genuine difference in landscape structure and predator pool.