The tundra is a vast, treeless biome characterized by extremely low temperatures and permanently frozen ground. Located primarily in the far Northern Hemisphere (Alaska, Canada, Siberia, and Greenland), it is often described as a polar desert due to low annual precipitation. The landscape consists of dwarf shrubs, sedges, mosses, and lichens. This article explores the biological limitations and adaptations that define the tundra, addressing whether this harsh environment supports high levels of biodiversity.
The Extreme Conditions Defining the Tundra
The primary factor limiting life in the tundra is the ground itself, which contains a layer of permanently frozen subsoil known as permafrost. This layer remains below 0°C for at least two consecutive years and can extend to depths of hundreds of meters. Permafrost prevents the deep rooting necessary for trees to grow, restricting vegetation to shallow-rooted, low-lying forms.
Above the permafrost is the active layer, which thaws during the brief summer months, typically only a few inches deep. Since the frozen ground below is impermeable, water cannot drain downward, causing the active layer to become saturated and boggy despite the low precipitation. The environment is also defined by extremely cold temperatures, with winter averages often dropping to around -28°C. The growing season is very short, lasting only about 50 to 60 days.
Species Richness and Ecological Diversity
The intense environmental constraints of the tundra result in characteristically low species richness compared to more temperate biomes. Species richness refers strictly to the number of different species present, and the tundra supports a restricted count of both flora and fauna. For instance, the entire Arctic tundra is home to only about 1,700 species of vascular plants and 48 species of land mammals.
This low diversity contrasts sharply with the population sizes of the few species that thrive there. This phenomenon, called ecological simplicity, means that while few species can survive the conditions, those that do often experience massive population booms. A single species, such as grass or the lemming, may be represented by millions of individuals. The food web is simple and susceptible to dramatic swings if a single species population collapses.
Survival Strategies of Tundra Organisms
The few species that successfully inhabit the tundra have developed remarkable adaptations to overcome the environmental challenges. Plants primarily adopt a low-growing, mat-like or cushion structure, which allows them to hug the ground and avoid abrasive winds. This prostrate growth form helps them benefit from the warmer microclimate just above the soil surface, where temperatures are significantly higher than the air above.
Plants employ several strategies to maximize survival during the short growing season. Many tundra plants are perennials that reproduce vegetatively rather than relying on setting seed. Some species, like the Arctic poppy, track the sun to maximize solar energy absorption, while others, like the wooly lousewort, are covered in thick, protective “fur” to defend against desiccation and cold. Insects, such as certain mosquitoes, possess high concentrations of glycerol, a natural “antifreeze,” allowing them to survive frigid winter temperatures.
Animals exhibit highly specialized traits to conserve heat and survive the cold, often termed a heat-efficient body shape. Mammals such as the Arctic fox and Arctic hare typically have smaller ears, shorter legs, and more compact bodies than their counterparts in warmer climates, minimizing heat loss. Insulation is provided by thick layers of fur or feathers, sometimes with a dense undercoat, and a layer of subcutaneous fat or blubber. Some animals, like the caribou, migrate to escape the harshest winter conditions, while smaller mammals, such as lemmings, build insulated tunnels beneath the snow layer.