In greening Arctic, caribou and muskoxen play key role
Study highlights importance of large grazing wildlife to Arctic ecosystem
image:
A group of muskoxen gather on the Arctic tundra near Kangerlussuaq, Greenland.
view moreCredit: Jeff Kerby
The story of Arctic greening has overlooked some main characters. At center stage are climate change and warming temperatures. Meanwhile, large grazing wildlife, such as caribou and muskoxen, also play a key role in the timing and abundance of Arctic plants, according to a study from the University of California, Davis.
The study, published today in the journal PNAS Nexus, highlights the importance of large herbivores to the Arctic ecosystem, linking grazing with plant phenology and abundance in the Arctic tundra.
Phenology is the study of the timing and cyclical patterns in nature, such as when birds migrate, or when a plant first sprouts or blooms. Understanding such patterns is critically important in the Arctic, which is warming faster than anywhere on Earth.
“Caribou and muskoxen play a key role in how soon plants emerge and this translates to how abundant they become,” said lead author Eric Post, a professor and arctic ecologist in the UC Davis Department of Wildlife, Fish and Conservation Biology. “This is an important, and overlooked, factor we need to consider as we seek to more fully understand climate change impacts on tundra vegetation in the Arctic.”
Exclusion experiment
The research was conducted at a long-term study site near Kangerlussuaq, Greenland, where Post has been studying plant and animal interactions for 22 years. To understand how herbivores affect the timing of plant growth and abundance, the scientists excluded caribou and muskoxen from some study areas. From 2009 to 2017, they compared the timing of spring green-up of nine plant species with and without the grazing animals.
In general, plants where caribou or muskoxen were present experienced earlier green-up and greater abundance later in the growing season. About two-thirds of plants greened up earlier, and three-quarters were more abundant later in the season compared to plots without grazing. These include arctic draba and gray willow.
Some species, including dwarf birch and harebell, emerged later with grazers present. Dwarf birch was the only species studied that did not increase in abundance under grazing. In all cases, the presence or absence of large grazing wildlife influenced how the plants responded.
Grazing awareness
Post said it is not yet clear why the plants respond in this way, but it is important to understand that there is a connection.
“We’re used to thinking of the timing of plant availability as impacting the productivity of grazing animals, but not the reverse,” Post said. “The absence or presence of herbivores can also impact the timing of plant growth and their productivity.”
This is especially important considering that many caribou populations in the Arctic are in decline. Migratory tundra caribou (Rangifer tarandus) are listed as vulnerable by the IUCN Red List and have lost more than half of their total abundance since the 1990s.
A separate study coauthored by Post and published Nov. 7, noted that supporting sustainable populations of herbivores in the Arctic could be a more effective nature-based solution to climate change in the region than planting trees there.
Co-authors for the PNAS Nexus study include UC Davis alum Conor Higgins of the Yolo County Resource Conservation District, Pernille Bøving of UC Davis, Christian John of UC Santa Barbara, Mason Post of the University of Washington, and Jeffrey Kerby of the Scott Polar Research Institute at Cambridge University. The authors give special thanks to the late Mads Forchhammer for his critical input and inspiring the study.
The study was funded by the U.S. National Science Foundation, National Geographic Society, European Union’s Horizon 2020 research program, and Aarhus University Research Foundation.
A caribou grazes grass and flowers in Greenland.
Credit
Eric Post, UC Davis)
Journal
PNAS Nexus
Method of Research
Experimental study
Article Title
Large herbivores link plant phenology and abundance in arctic tundra
Article Publication Date
12-Nov-2024
Article Publication Date
12-Nov-2024
Plant green-up and herbivory in Greenland
PNAS Nexus
image:
Male muskoxen near Kangerlussuaq, Greenland
view moreCredit: Eric Post
A study links herbivory to phenology in the Arctic. Phenology is the study of the timing of events in the natural world. In recent decades, researchers have investigated how climate change is shifting many natural events. Eric Post and colleagues wanted to understand how a different variable—the presence or absence of herbivores—affects the timing of spring plant growth, or green-up, in Greenland. In an experiment lasting nine years, the authors excluded musk oxen and caribou from some areas, then compared the timing of the spring green-up of 9 tundra plant species in the areas with and without herbivores. Of the plants that showed altered green-up between the conditions, about two-thirds showed earlier green-up in plots with grazing than in plots without, including Draba nivalis, yellow arctic draba, and Salix glauca, gray willow. A few plants, including Betula nana, the dwarf birch, and Campanula Gieseckiana, harebell, showed later green-up under herbivory than under herbivore exclusion. The team also measured plant abundance. Of the plants that showed a response to grazing, 75% were more abundant in the plots with herbivores. In general, early green-up under herbivory led to high abundance later in the growing season. The only plant that did not see increased abundance in plots with herbivores as compared to plots without herbivores was dwarf birch, which was also the most common species on the study plots. According to the authors, herbivory that reduced birch cover likely also reduced shade on other species, hastening and boosting their growth.
Arctic harebell near Kangerlussuaq, Greenland
Male caribou near Kangerlussuaq, Greenland.
Male caribou near Kangerlussuaq, Greenland.
Female muskoxen and calves near Kangerlussuaq, Greenlan
Female muskoxen and calves near Kangerlussuaq, Greenlan
Credit
Eric Post
Journal
PNAS Nexus
Article Title
Large herbivores link plant phenology and abundance in Arctic tundra
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