In many ways the tundra is similar to the desert or the grasslands. The plant and animal life must find ways to adapt to a rigorous climate that provides little rain, and frequent extremes in temperature. In the tundra the average annual rainfall ranges from 12 to 20 inches, but the permafrost keeps this small amount of moisture near the surface. About 85% of Alaska and 50% of Canada has this permafrost and it is one of the defining characteristics of the tundra. During the summer months the top layer of the soil thaws only a few inches down and so the water is trapped on the surface forming numerous shallow lakes, ponds, and bogs. Although the winter temperatures can reach Ð60°F, the temperatures in the summer can climb well into the 60s and 70s. This summer heat and the moisture it releases, as well as the extremely long day, make a surprisingly abundant quantity of vegetation possible. The growing season may be as much as two to three and a half months long but in many places the soil temperature rarely gets much above the freezing point. Generally the soil is rather thin as the cold temperatures inhibit the growth of bacteria and other soil-producing organisms.
Despite the cold conditions some plants need only a few days above 32
°
F to survive. The lichens, mosses, and algae are among the most common plants to be found there. Lichens are a symbiotic partnership of fungi and algae; the fungi anchors itself to a rock and its spongy tissue holds large quantities of water, while the algae lives inside this moist shelter photosynthesizing food which it shares with the fungus. Most lichens grow at a remarkably slow rate, in some cases as little as one mm per year. One type of lichen called reindeer moss does grow relatively quickly and may be six inches tall. It often forms dense mats of vegetation that provide nourishment for caribou and musk ox.
Flowering plants in the tundra require at least two months of growing season although there are a few hardy souls that can manage on only a few weeks. Since even the summer season may present the challenge of an overnight freeze most of the successful plants are perennials which will have many years over which they may try to produce flowers and seeds. Some arctic plants have virtually given up reproduction by seed and spread exclusively by vegetative means. Many of the hardy plants have most of their body tissue below ground waiting for spring. Even the new buds may be formed in the fall and stored underground until warm temperatures arrive. The warm weather signals the plant to produce flowers and seeds quickly using the reserves stored from the previous year for growth. After the seeds are formed the plant can then renew itself by photosynthesis. Some of the other adaptations these plants have evolved include a low growing stature. Some willows, alders, and birches will be only a few inches tall but spread over a wide area, ten to fifteen feet across. Some plants have large leaves that angle toward the sun for maximum solar reception, the leaves or flowers may also be relatively dark in color to be more heat absorptive. The stems can be hollow using less nutrients in their growth, and the stems or leaves might be wooly to insulate themselves from the cold. Many of the tundra plants are found growing in masses or cushions to deflect the wind and conserve heat energy.
The rigors of arctic life are equally trying for the animals of the tundra. With very few exceptions the animals are all warm-blooded. When the temperature around them drops to freezing they are able to maintain the appropriate body temperature by metabolizing large quantities of stored fat or taking in sufficient amounts of food. Although this production of body heat is an ongoing constant need, arctic animals have evolved several ways to hold onto much of the heat they generate. Their primary heat-preserving mechanism is insulation; a layer of fat just beneath the skin and a thick layer of fur or feathers over the skin. Often these feathers or fur hairs are hollow which acts even more efficiently as an insulating layer. Some animals are able to live comfortably under the snow in tunnels they have made, living on caches of seeds and leaves safe from most predators (until their snow home melts in spring). Some animals are true hibernators that curl up in dens for the winter. Their body temperatures may drop almost to the freezing point and their stored fat provides the small amount of nourishment their bodies need while in this suspended state. Many of the tundra inhabitants migrate to more favorable environments. The classic example is the Arctic tern which flies between its summer and winter homes in the Arctic and Antarctica every year. It is on the wing about seven months of every year and flies some 21,000 miles. It has chosen the Arctic tundra for its mating and nesting habitat!
Many kinds of migratory birds, including geese, swans, ducks, gulls, ravens, and owls, have claimed the tundra as their favored nesting site. The abundance of open water provides an ideal breeding ground for millions of insects. This means a generous source of food for the birds and their offspring and the almost continuous daylight enables the parents to gather food night and day resulting in very rapid fledgling growth. An interesting arctic bird is the ptarmigan. It is a year-round resident and finds a variety of things to eat, chiefly berries and new shoots in the summer and willow buds in the winter. The ptarmigan is considered good-eating by a number of tundra predators and so the ptarmigan has evolved protective coloration, camouflage, to protect itself. In the summer its feathers are brown-speckled blending in with its ground cover surroundings, and in the winter new feathers come in that are snow white making it almost impossible to spot. Another well camouflaged bird is the snowy owl. It stays year-round also and nests and lays its eggs while the snow is still on the ground. One of its main prey species is the lemming, which is active year round.
Lemmings are the favorite meal of many of the tundra’s predators. They mate and produce young most of the year, as many as eight litters of five to ten young pups each year. Lemmings eat grasses and seed constantly producing an abundance of wastes which fertilize the grass growth. But sometimes they take so much that the area is striped bare of plant life and it can take years to regrow. As the lemming population grows it migrates in its search for more food, as it travels the group grows in size and the damage it does to the vegetation is considerable. As the population peaks in number hormonal and chemical changes seem to cause a mass die-off and the animals disappear from the scene for awhile. They do not however as legend has it jump into the sea in a mass suicide frenzy.
Caribou and musk ox are two of the tundra’s large herbivores that have found ways to survive the hostile climate. The caribou migrates over five hundred miles in its travels from winter to summer grounds. The caribou has large hooves so they won’t sink into the muddy ground or the snow. Their fur is a thick coat of hollow hairs and both males and females have antlers. Their calving grounds are in the tundra where they feed on sedges, grasses, willow, birch, and even a trampled lemming or two. In the winter they move further south and feed on lichens in forested areas. Golden eagles and bears prey upon the calves, and wolves will take an adult especially if it is old or weakened. Insects also prey upon the caribou and can take four ounces of blood from one animal in a day. A more rare animal of the tundra is the musk ox. It feeds on grasses and willows and although it moves from upland to lowland areas during the year it stays within the tundra biome. Its long curly fur covers another layer of soft wooly fur making an almost perfect insulating coat. It spends much of its day conserving energy by sleeping on the ground. The snow beneath these shaggy beasts compacts but does not melt proving the efficiency of their fur.
An occasional visitor to the tundra from its pack ice home is the polar bear. It spends most of its time on ice floes or in the water where its thick layer of fat and dense coat of oily fur keep it warm and the favored prey, seals and fish can be constantly obtained. On the polar bear’s rare visits to regions on land it will feed on berries, grasses, and rodents. A pregnant female bear will find a cave in the ice to hibernate in. She gives birth to her cubs during the winter. A seven hundred pound polar bear mother delivers a two pound offspring which she will care for for at least two years.
An activity that would fit in with the study of the tundra is the examination of lichens and mosses. Many varieties are available for easy collection and could be maintained in a terrarium in the classroom. Activity 2 gives some suggestions for looking at both lichens and mosses.