As northern winters grow increasingly erratic—with snow arriving late, melting early and packing thin—researchers have identified an unexpected ally in northern Finland’s conifer woods: the reindeer. It follows a multi-year snow-manipulation experiment at the University of Oulu, published in Science of the Total Environment last week, which shows that where herds graze, summer carbon release remains stable, even after shallow or deep snowpacks.
Between 2019 and 2023, scientists compared three snow treatments—ambient, reduced (25 cm) and increased (added snow)—across grazed plots and long-term exclosures at two sites: Oulanka (25 years without reindeer) and Kevo (55 years). They measured understory net ecosystem exchange (NEE), ecosystem respiration (ER) and gross ecosystem production (GEP) throughout the growing seasons.
At Kevo’s 55-year exclusion, reduced snow triggered a 205% spike in net CO₂ release compared to grazed areas under the same conditions, while deeper snow cut emissions by up to 134%. “It is possible that at Kevo, the substantially recovered lichen cover has influenced soil temperature and moisture conditions,” explained lead author Noora Kantola. Those thick lichen mats insulate soil, shape moisture retention and fuel microbial decomposition once spring arrives.
By contrast, carbon flux in grazed plots—and even in Oulanka’s 25-year exclosure—remained remarkably stable across all snow depths. “Reindeer grazing can buffer ecosystem functions, such as carbon exchange, under changing climate conditions,” said senior author Maria Väisänen, highlighting how herbivores keep insulating lichen layers thin and patchy.
Grazing’s influence extends beyond carbon: it reshapes understory biodiversity, from mosses to saplings. “The lichen-mediated impacts of grazing on the understory carbon exchange of winter pastures can be significant,” added Jeffrey Welker, emphasising that reindeer affect everything from nutrient cycling to tree growth patterns. For forest managers, the takeaway is clear: in long-protected areas where lichen carpets have thickened undisturbed, oddball winters could trigger large summer carbon pulses. Reintroducing controlled reindeer grazing may serve as a nature-based adaptation, dampening those swings and bolstering ecosystem resilience.
The findings underscore a broader principle: large herbivores worldwide—from bison to caribou—modulate vegetation structure and soil microclimates, buffering ecosystems against extreme weather. As winters continue to change, the reindeer may prove indispensable in maintaining the boreal forests’ carbon.
For more information: Noora Kantola, Jeffrey M. Welker, A. Joshua Leffler, Juho Lämsä, Riku Paavola, Otso Suominen, Maria Väisänen, Impacts of winter climate change on northern forest understory carbon dioxide exchange determined by reindeer grazing, Science of The Total Environment, Volume 995, 2025, 180089, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2025.180089.
