Consequences of warming on tundra carbon balance determined by reindeer grazing history

Abstract

Large parts of the circumpolar Arctic are grazed by reindeer but the effects of grazing pressure on ecological responses to climate change, and the associated climate feedbacks, remain unclear. Now, research using a long-term environmental manipulation experiment finds that although warming decreased the carbon sink of tundra experiencing light grazing pressure, it had no effect on tundra under high grazing pressure. Arctic tundra currently stores half of the global soil carbon (C) stock1. Climate warming in the Arctic may lead to accelerated CO2 release through enhanced decomposition and turn Arctic ecosystems from a net C sink into a net C source, if warming enhances decomposition more than plant photosynthesis2. A large portion of the circumpolar Arctic is grazed by reindeer/caribou, and grazing causes important vegetation shifts in the long-term. Using a unique experimental set-up, where areas experiencing more than 50 years of either light (LG) or heavy (HG) grazing were warmed and/or fertilized, we show that under ambient conditions areas under LG were a 70% stronger C sink than HG areas. Although warming decreased the C sink by 38% under LG, it had no effect under HG. Grazing history will thus be an important determinant in the response of ecosystem C balance to climate warming, which at present is not taken into account in climate change models.

Cite this article

Väisänen, M., Ylänne, H., Kaarlejärvi, E. et al. Consequences of warming on tundra carbon balance determined by reindeer grazing history. Nature Clim Change 4, 384–388 (2014). https://doi.org/10.1038/nclimate2147

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