The Arctic is undergoing rapid and unprecedented changes due to climate change, such as rising temperatures, melting sea ice, and thawing permafrost.
These changes have profound impacts on the biodiversity and ecosystems of the region, which host a unique and diverse array of plants, animals, and microorganisms.
However, a new study suggests that some large herbivores, such as caribou and muskoxen, may help to buffer the effects of climate change on tundra biodiversity by grazing on shrubs and other plants that would otherwise dominate the landscape.
The study was published in the journal Science.
How climate change affects tundra biodiversity
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The tundra is a biome that covers about 20% of the Earth's land surface, mostly in the Arctic.
It is characterized by cold and dry conditions, short growing seasons, and low vegetation that consists mainly of grasses, sedges, mosses, lichens, and dwarf shrubs, as per Phys.org.
The tundra supports a rich diversity of life forms, including mammals such as caribou, muskoxen, polar bears, wolves, and foxes; birds such as snowy owls, ptarmigans, and geese; and insects such as mosquitoes, flies, and beetles.
Climate change poses a major threat to tundra biodiversity, as it alters the physical and biological factors that shape the ecosystem. For example:
Rising temperatures increase the length and intensity of the growing season, which favors the growth and expansion of shrubs and trees at the expense of other plant species. This process, known as shrubification or greening, reduces the diversity and abundance of plants and animals that depend on open habitats.
Melting sea ice reduces the albedo or reflectivity of the surface, which amplifies the warming effect. It also affects the availability and quality of food and habitat for marine mammals such as seals, walruses, and polar bears, as well as for coastal birds such as eiders and terns.
Thawing permafrost releases greenhouse gases such as carbon dioxide and methane into the atmosphere, which further contributes to global warming. It also causes land subsidence or sinking, which alters hydrology and vegetation patterns. It also exposes organic matter that was previously frozen to decomposition by microbes and fungi.
Changing precipitation patterns affect soil moisture and nutrient availability for plants. They also influence snow cover and depth, which affect plant survival, animal distribution, and predator-prey interactions.
These changes have already resulted in observable declines in tundra biodiversity across different taxonomic groups and spatial scales.
For instance, a recent study found that plant diversity in the Arctic has decreased by about 5% over the past three decades.
How caribou and muskoxen help to slow biodiversity loss
Caribou (Rangifer tarandus) and muskoxen (Ovibos moschatus) are two iconic herbivores of the Arctic tundra, as per France 24.
They feed on a variety of plants, including grasses, sedges, forbs, lichens, mosses, and shrubs. They also migrate across large distances in response to seasonal changes in food availability and quality.
A team of researchers from Canada, Denmark, Norway, Sweden, Switzerland, the UK, and the US conducted a large-scale experiment to test how caribou and muskoxen affect tundra biodiversity under climate change.
The experiment involved 12 sites across four Arctic countries: Canada (Nunavut), Greenland (Kangerlussuaq), Norway (Svalbard), and Sweden (Abisko).
At each site, the researchers set up four types of plots: fenced plots that excluded herbivores; open plots that allowed herbivores; warmed plots that increased temperature by about 1°C using open-top chambers; and control plots that were left undisturbed.
The researchers monitored the plots for four years (2016-2019) and measured various indicators of biodiversity, such as plant species richness (the number of different plant species), plant functional diversity (the diversity of plant traits related to growth, reproduction, resource use), plant biomass (the amount of plant material), soil microbial diversity (the diversity of bacteria and fungi in the soil), soil carbon content (the amount of organic carbon in the soil), and soil nitrogen content (the amount of nitrogen in the soil).
The results showed that caribou and muskoxen had a positive effect on tundra biodiversity by reducing shrub cover and increasing plant species richness and functional diversity.
These effects were stronger in warmed plots than in control plots, indicating that herbivores can counteract some of the negative impacts of climate warming on tundra vegetation.
The researchers also found that herbivores had a positive effect on soil microbial diversity by increasing soil carbon and nitrogen content through their feces and urine.
They concluded that caribou and muskoxen play a key role in maintaining and enhancing tundra biodiversity in the face of climate change.
These experts suggested that conserving and restoring these large herbivores could be an effective strategy to mitigate the loss of tundra biodiversity and ecosystem services.
They also called for more research on the interactions and feedbacks between herbivores, plants, microbes, and climate in the Arctic.
