Lemmings drive short- and long-term vegetation and carbon dynamics in coastal tundra: resampling historic herbivore exclosures at Barrow, Alaska

Background/Question/Methods

In many ecosystems, herbivores can regulate a range structural and functional attributes including primary productivity, species composition and cycling of nutrients. In the Arctic however, the strength and direction of ecosystem responses to herbivory have been difficult to detect and often vary widely among tundra types. In the coastal tundra near Barrow Alaska, fluctuations of lemming populations have long intrigued researchers and exclosure treatments were established at various periods between the 1950’s (Naval Arctic Research Laboratory) and early 1970’s (International Biological Program). Approximately 25% of these exclosures and adjacent control plots remain intact and were sampled in 2002 and 2010. We believe these plots are the oldest herbivore exclosures in the Arctic and provides a unique opportunity to evaluate ecosystem structure and function under sustained herbivore exclusion .

Results/Conclusions

Plant cover and abundance as well as biomass estimates indicate that the response to herbivory differs markedly among plant communities spanning a soil moisture gradient. While herbivore exclusion resulted in a decrease in vascular plant abundance and diversity in all communities, lichens increased in drier sites and mosses increased in wetter sites. Exclusion also resulted in differences in functional attributes. In the wet tundra, exclusion increased albedo and decreased thaw depth, NDVI (normalized difference vegetation index), and CO₂ uptake potential. Drier sites showed little difference in CH₄ flux, while moist and wet sites showed significant decreases in CH₄ efflux in the absence of herbivores. These results suggest that herbivores have a strong regulatory impact on ecosystem structure and function in this coastal tundra. Because theoretical, observational and experimental data show that primary productivity has increased as the Arctic has warmed, herbivore populations and their role as ecosystem drivers are likely to changing as well. This study provides experimental data supporting this conjecture from what we believe are the oldest intact herbivore exclosures in the Arctic.