Not all climate heroes wear capes. Some sport antlers. New research, published in Science of the Total Environment, shows that when reindeer graze the snow-covered understories of Finland’s northern forests, the herbivores help to stabilise the carbon that is locked away there.
Northern forests store about a third of the world’s terrestrial carbon. Trees are an important sink, but so is the soil and also the low-growing plants that are eaten by reindeer.
Researchers from the University of Oulu wanted to investigate how reindeer grazing and snow cover affect the carbon cycle. So, they ran experiments between 2019 and 2023 in areas where reindeer graze and areas where grazing has been excluded for decades – for 25 years at Oulanka in eastern Finland and 55 years at Kevo in northern Finland. In both environments, they manipulated the snow to produce deeper and shallower patches and then looked to see how this affected carbon release during the following growing season in summer.
In the area that had been ungrazed for 55 years, snow depth had a big effect. Shallow snow increased carbon release from the understory and soil. Deeper snow decreased it. But in the areas with ongoing grazing – and even in the 25-year site at Oulanka - carbon release stayed stable regardless of changes in snow cover.
“Altogether, this could indicate that northern coniferous forests may be relatively well resistant to short-term changes in winter climate,” says the study’s lead author, Noora Kantola.
Grazing has a buffering effect that helps to stabilise the carbon cycle, but when the grazing stops, the effect eventually wears off. This explains the differences seen between the sites at Oulanka and Kevo.
Researchers think this is because of the resulting changes to the understory. Decades without grazing allows the lichen to recover, in turn affecting how warmth and water move between air and soil.
“It is possible that at Kevo, the substantially recovered lichen cover has influenced soil temperature and moisture conditions. Together with changing snow depth, these factors may affect soil decomposers and thereby the amount of carbon released,” says Noora Kantola, from the study team.
The take home message is that when reindeer are allowed to do what reindeer to best – grazing and trampling vegetation – it’s not just good for them or the northern forests they inhabit. It’s potentially good for the health of the planet too.
Top image: reindeer grazing. Credit: Noora Kantola / the University of Oulu
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