| Current global warming urgently calls for a better understanding of how ecosystems respond to environmental changes. However, recent findings show that the effects of global warming on tundra ecosystems cannot be predicted in an accurate way without considering biotic interactions. Linking population and ecosystem ecology, and finding tools to study these processes at landscape scales would be one way to achieve that. In this project, we will address complex ecological questions at an adequate spatial scale by combining satellite images and long-term experiments. We will compare data from herbivore exclosures with NDVI estimates from satellite images to study the effects of voles and lemmings on tundra ecosystems at landscape scales. My preliminary research (Fig. 1) show that the regular fluctuations in densities of small rodents drive cycles in plant biomass that can be recorded even at the landscape scale (100km2). These fluctuations are so pronounced because all dominant plants fluctuate in synchrony. However, the amplitude of the fluctuations is species specific and may depend on plants resistance and resilience traits. The relative abundance of plants with different traits is thus expected to differ between phases of the small rodent cycle. Since the same traits that make a plant resistant or resilient to herbivory also influence the quality of the litter they produce, these vegetation changes are also expected to result in cycles in the quality of litter that could be important for the carbon and nitrogen turnover during different phases of the cycle. By studying plant community composition and elemental fluxes simultaneously, I will be able to link plant population changes to ecosystem processes. The importance of these results can be evaluated for whole landscapes by combining it with the data from satellites. Moreover, my preliminary data indicate that NDVI from satellite images may provide a powerful tool to study vole and lemming cycles. This could be a new cost-effective way to monitor voles and lemmings in the future, and make it possible to reconstruct the vole and lemming dynamics in tundra ecosystems for the last 40 years. This new long-term and large-scale data could enable us to finally answer some of the questions that have puzzled researchers for more than half a century. |