What Is the Tundra? The Treeless Land at the Top of the World
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North of the last trees, a belt of land runs around the top of the world where the ground is frozen for most of the year, the plants are ankle-high, the sun does not set in June and does not rise in December, and a fifth of the Earth's land surface is covered by a landscape that most people have never seen. The word tundra comes from a Sami word for a treeless height, and the absence of trees is the definition: the tundra is where the summer is too short and too cold for a tree to make enough wood to survive the winter, and everything else about it follows from that.
Where it is and why
Arctic tundra circles the pole north of the boreal forest, across Alaska, northern Canada, Greenland's coast, Iceland, Scandinavia and the whole northern edge of Russia, with a much smaller Antarctic version on the peninsula and the islands of the Southern Ocean. Alpine tundra occurs wherever mountains rise above the treeline, from the Rockies and Alps to the Andes and the Himalaya, and it is similar in look and different in detail, since it has ordinary days and nights and steep, well-drained slopes. The Arctic kind is defined by a summer of six to ten weeks with average temperatures barely above freezing, annual precipitation as low as a desert's, 150 to 250 millimetres, most of it snow, and permafrost beneath the surface that stops water draining away, so that a dry climate produces a wet landscape of bogs and ponds every summer.
The plants
Nothing grows tall. The plants of the tundra are mosses, lichens, sedges, grasses, low flowering herbs and dwarf shrubs, willows and birches that grow as mats a few centimetres high and may be a century old, and they share a set of tricks for a place that gives them two months a year:
- •Staying low, where the wind is weaker and the air near the dark ground is warmer, and where snow covers them in winter as insulation
- •Growing in cushions and mats that trap heat and hold soil
- •Keeping most of their mass underground in roots and rhizomes that survive the winter and sprout the moment the snow melts
- •Flowering fast, often within days of thaw, with dark or cup-shaped flowers that track the sun and warm their own seeds
- •Reproducing by runners and bulbils as well as seed, since a summer may end before seed ripens
- •Lichens, a fungus and an alga together, growing on bare rock and feeding the reindeer through winter
The animals
The year has two states, and the animals are divided by how they handle the winter. Some stay: musk oxen with coats to the ground, Arctic foxes and hares that turn white and grow fur on the soles of their feet, lemmings that live under the snow in tunnels and whose population booms and crashes on a three- to four-year cycle that drives the numbers of everything that eats them, and ptarmigan that dig into drifts to sleep. Most leave. The tundra in summer is the largest nursery on Earth for birds, with hundreds of millions of geese, ducks, waders and songbirds flying in from as far as Argentina and South Africa to breed in a season when the insects hatch by the ton and the daylight never ends, and leaving in August. The caribou of North America and the reindeer of Eurasia, the same species, migrate in herds of hundreds of thousands between the tundra where they calve and the forest where they winter, on the longest land migrations of any mammal.
The soil that is not there
Tundra soil is thin, acidic and waterlogged, and it holds almost no nutrients in a form plants can use, because cold stops the decomposition that would recycle them. Dead plants do not rot; they pile up as peat, and the carbon in the tundra's peat and permafrost, accumulated over ten thousand years of summers, is one of the largest stores on the planet. That is why the biome matters far beyond its borders. The Arctic has warmed about four times faster than the global average, the tundra is greening, with shrubs advancing north and growing taller in satellite images since the 1980s, the treeline is creeping poleward, and the thaw is releasing carbon dioxide and methane from ground that was a freezer, a feedback that makes the tundra one of the levers of the whole climate.
People
Humans have lived on the tundra for at least 30,000 years, and the peoples there now, the Inuit of Canada and Greenland, the Sami of Scandinavia, the Nenets, Chukchi and dozens of others across Siberia, built cultures around the caribou, the seal and the whale, with technologies, the kayak, the snow house, the toggling harpoon, the reindeer sledge, that Europeans copied when they arrived. The land is also where much of the world's oil, gas, nickel and diamonds lie, and the roads, pipelines and mines that reach them are what has changed the tundra most in a century, along with the warming that is now changing it faster. It remains one of the emptiest places on Earth, with more caribou than people, and the one biome where a visitor can still walk for a week without crossing a track.
The takeaway
The tundra is the treeless biome around the Arctic and above the treeline on mountains, where a summer of a few weeks above freezing, low precipitation and permafrost produce a wet, boggy landscape of mosses, lichens, sedges and dwarf shrubs that hug the ground and grow fast. It is wintered by a few insulated animals and visited in summer by hundreds of millions of breeding birds and migrating caribou, its frozen peat holds a huge store of carbon, and it is warming and greening faster than anywhere else.