In this paper published in Functional Ecology, Henni Ylänne and collaborators investigate the impact of reindeer on the carbon storage at two sub-arctic tundra sites in Northern Norway. The sites represent typical examples of herbivory-induced alternative ecosystem states, where high grazing pressure has led to a conversion of tundra shrublands or heaths to tundra meadows with higher rates of nutrient turnover. This study makes use of two 60-year-old reindeer fences that separate these alternative ecosystem states, and compares recent changes in above- and belowground carbon storage.
The paper reports that in the past 14 years, the increased reindeer numbers and higher trampling intensity have led to a larger areal extent of grass-dominated vegetation, leading also to higher soil nutrient availability. This demonstrates the capacity of tundra systems to adjust to changes in grazing pressure.
Further, the paper shows that the “grassification” of tundra shrublands, whether occurred recently or decades earlier, reduces carbon stored aboveground. However, the impacts of grazing belowground varied between the two study sites. At one site, the grass dominated, grazed area stored equal amounts of carbon compared to the tundra heath. At the other site, there was more carbon in the organic soil under the grass-dominated, grazed area compared to the shrub tundra. The consequences of grazing depend on the characteristics of the vegetation under light grazing.
Reference: Ylänne, H., Olofsson, J., Oksanen, L., Stark, S. (2018) Consequences of grazer‐induced vegetation transitions on ecosystem carbon storage in the tundra. Functional Ecology 32: 1091– 1102.
https://doi.org/10.1111/1365-2435.13029
Picture: Differences in vegetation across the reindeer fence in
Čearro (photo: Henni Ylänne, Lund University, 2018)