A recent study sheds light on the crucial role of caribou and muskoxen in the flourishing Arctic tundra, connecting their grazing habits to the growth and timing of plant life in the region.
While climate change and rising temperatures are often seen as the main players in the story of Arctic greening, significant contributions come from large grazing animals like caribou and muskoxen. A study conducted by researchers at the University of California, Davis, reveals how these animals influence the emergence and abundance of Arctic vegetation.
Published today in PNAS Nexus, this research emphasizes the vital role large herbivores play in the Arctic ecosystem, establishing a link between grazing behaviors and the timing and growth of plants in the tundra.
Phenology, which studies the timing of natural events—such as bird migrations or plant blooming—is especially crucial in the Arctic, the fastest-warming region on the planet.
According to Eric Post, the lead author and a professor of Arctic ecology at UC Davis, “Caribou and muskoxen are essential in influencing when plants emerge, which in turn affects their overall abundance. Recognizing this factor is vital for a full understanding of how climate change is impacting tundra vegetation in the Arctic.”
Exclusion experiment
The research took place at a long-term study site close to Kangerlussuaq, Greenland, where Post has dedicated 22 years to examining plant and animal interactions. To assess the impact of herbivores on plant growth timing and abundance, researchers created areas where caribou and muskoxen were excluded. From 2009 to 2017, they compared the spring green-up timing of nine plant species in plots with and without the grazers.
Overall, in areas where caribou or muskoxen grazed, plants tended to green up earlier and show greater abundance as the growing season progressed. Approximately two-thirds of the plants began to grow earlier, and three-quarters were more abundant later in the season compared to areas without grazing. Among these were species such as arctic draba and gray willow.
However, some species, including dwarf birch and harebell, had delayed growth in the presence of grazers. Notably, dwarf birch was the only species studied that did not show an increase in abundance with grazing. In all instances, the presence or absence of large grazing fauna affected the plants’ responses.
Grazing awareness
Post noted that the reason behind these plant responses remains unclear, yet it is crucial to acknowledge the interconnection.
“We typically consider how the timing of plant growth impacts grazing animal productivity, but it’s important to recognize that the presence or absence of herbivores can also affect plant growth timing and productivity,” Post explained.
This insight is particularly significant given the current decline in many Arctic caribou populations. The migratory tundra caribou (Rangifer tarandus) are classified as vulnerable by the IUCN Red List, having lost over half of their overall population since the 1990s.
Additionally, a separate study co-authored by Post and published on November 7 suggests that maintaining sustainable herbivore populations in the Arctic might be a more effective, nature-based approach to addressing climate change in the region than merely planting trees.
Other contributors to the PNAS Nexus study include UC Davis graduate Conor Higgins from the Yolo County Resource Conservation District, Pernille Bøving from UC Davis, Christian John from UC Santa Barbara, Mason Post from the University of Washington, and Jeffrey Kerby from the Scott Polar Research Institute at Cambridge University. The authors extend special gratitude to the late Mads Forchhammer for his significant input and inspiration for this research.
The study received funding from the U.S. National Science Foundation, National Geographic Society, European Union’s Horizon 2020 research program, and Aarhus University Research Foundation.
