The Arctic is warming faster than the rest of the planet, accelerating the thaw of permafrost, the permanently frozen ground covering vast northern regions. Permafrost holds an immense reservoir of ancient organic carbon which, if released as carbon dioxide and methane, could worsen global warming. A proposed solution involves “rewilding” the Arctic by reintroducing large herbivores, such as the woolly mammoth or their proxies like bison and horses, to restore the productive grassland ecosystem. This strategy leverages the animals’ natural behaviors to stabilize the permafrost through thermal regulation, changes in surface reflectivity, and enhanced soil carbon storage.
The Core Concept of Steppe Ecosystem Restoration
The Arctic was once covered by the “Mammoth Steppe,” a grassland biome maintained by immense herds of large grazing animals, including mammoths, bison, and horses. When the megafauna population declined about 10,000 years ago, the ecosystem shifted to the current landscape of low-productivity mosses, shrubs, and boreal forests (taiga) that dominate the tundra.
Mammoths acted as ecological engineers, using their size and feeding habits to maintain the grassland structure. These animals grazed on grasses and forbs while trampling and uprooting the woody shrubs and small trees that now insulate the ground. This constant disturbance prevented the encroachment of the darker, less productive vegetation characterizing the Arctic. Restoring this grazing dynamic is the primary step to transform the tundra back into a carbon-sequestering steppe.
Mitigating Permafrost Thaw Through Snow Compaction
A thick layer of snow acts as a powerful insulator, trapping the ground’s residual heat and preventing the extremely cold winter air from penetrating the soil. In the modern tundra, this snow blanket keeps the permafrost warm enough to risk thawing during the summer months.
Large herbivores like mammoths, or their substitutes, interrupt this process by trampling and compacting the snow while foraging for winter forage. Their massive weight and constant movement crush the air pockets within the snow, substantially reducing its insulating capacity. This compaction allows the frigid Arctic air to reach deeper into the ground.
By exposing the soil to lower temperatures, the animals cause the permafrost to freeze more deeply and maintain a colder mean annual temperature. Studies conducted in rewilding sites, such as Russia’s Pleistocene Park, have shown that grazed areas exhibit a significant drop in soil temperature compared to ungrazed areas. This deeper, colder freeze provides a thermal buffer that helps prevent the permafrost from thawing during the warmer summer season.
Increasing Surface Reflectivity and Albedo
The conversion of the landscape from tundra to grassland affects how the Arctic surface interacts with solar radiation, known as albedo. Albedo measures how much sunlight a surface reflects; a high albedo promotes cooling by reflecting more sunlight back into space. The current Arctic landscape, dominated by dark shrubs and coniferous trees, absorbs considerable solar energy.
These dark surfaces have a low albedo, meaning they trap heat and contribute to regional warming, accelerating permafrost thaw. Grasslands are lighter in color and reflect more sunlight, resulting in a higher albedo. This difference is pronounced when the lighter grass is covered by snow, which reflects nearly all incoming solar radiation.
The constant grazing and trampling by large herbivores suppress the growth of dark woody vegetation, allowing reflective grasses to dominate. By maintaining a lighter-colored surface, the restored steppe ecosystem absorbs less solar heat throughout the year. This increased surface reflectivity cools the ground and delays the seasonal thaw of the active layer above the permafrost.
Enhancing Soil Carbon Storage
The shift to a steppe ecosystem changes the fundamental carbon cycle of the soil. Intense grazing stimulates the growth of productive steppe grasses, which have deep, robust root systems. As these roots grow and die annually, they deposit atmospheric carbon deep into the ground, sequestering it more effectively than the shallow-rooted mosses and shrubs of the tundra.
The presence of large herbivores enhances nutrient cycling, supporting the high productivity of the grasses. Grazing removes old plant matter, which prevents the buildup of detritus on the surface that can otherwise release greenhouse gases. The animals’ dung also fertilizes the soil, promoting the health and growth of the deep-rooted grasses, effectively locking carbon away. Megafauna help transform the Arctic from a potential carbon source into a more efficient carbon sink.