Tundra. The word comes from Russia and means “land of no trees”.
The popular image of tundra is that of the arctic barrens – a land of Musk-ox and Polar Bears. But, in fact tundra conditions occur down the entire length of North America at or near the tops of the high mountains.
Alpine tundra as opposed to arctic tundra lies in the zone between the upper tree limit and the lower limit of permanent snow. There are no Polar Bears here but there are Caribou – Woodland Caribou.
An elevation gain of one thousand feet is about the equivalent of traveling five hundred miles north. Thus in the Arctic tundra conditions occur at sea level; in northern British Columbia the same conditions are found at six thousand feet (Pink Mountain is 5800 ft) in southern British Columbia at eight thousand feet and in the Colorado Rockies at fourteen thousand feet.
The particular conditions that define alpine tundra combine to create one of the most harsh plant habitats on earth. Because it is so close, the sky dominates and the wind is a constant, physical presence.
The lowering afternoon sun allows the upper air to cool first. Cooler air, being heavier, slides downward into the valleys creating down-
slope winds. In the early morning the sun warms the valley bottoms and the lower air begins to rise causing strong up-slope winds. Thus there is rarely a windless moment on the alpine tundra.
The wind mercilessly batters any plant that dares raise its head more than a few inches above the ground. And in winter the wind becomes an even greater force, sweeping most of the tundra bare of snow and piling up drifts on lee slopes and in depressions. Any tree that protrudes beyond the shelter of a rocky outcrop or snow bank is quickly destroyed by the abrasion of wind-driven ice crystals. It is common on the tundra to find plants huddling in the shelter of rocks for it is only there that they may escape the mechanical pruning of the wind.
Even in summer the wind is detrimental to plants. It sucks up scarce moisture from the ground and from plant tissue. Within minutes of a heavy rain the ground surface will be blotted dry by the wind and desiccation is a serious problem for the plants.
The constant stirring prevents even a hot sun from effectively warming the air thus ground level temperatures are always low.
The tundra has been referred to as a near desert. Little precipitation falls in either summer or winter providing insufficient snow for winter protection and making the acquisition and conservation of moisture a major priority for the plants.
Many summer days begin with a cloudless blue sky but by mid morning the moisture in rising valley air is condensing into small white puffs of cloud, which grow rapidly into lowering cumulus. By early afternoon local thunderstorms begin to occur. The thunderstorms are short but violent. Strong, gusty winds and driving rain batter the tundra. And often, even in midsummer, the rain is accompanied by hail.
Flowers are devastated but unopened buds are unharmed and will complete the essential task of seed production.
Violent as they are, these daily storms are essential to the tundra. The storms are the major source of moisture for most of the plants. Without the storms the tundra would be uninhabitable for many shallow rooted species. The plants have adapted to cope with storm damage, so in the end, the storms are and asset rather than a liability.
Although drenching rain may fall for and hour or two the moisture is not long available to most plants. The rocky substrate drains quickly and the bright sun, which usually follows a storm, causes rapid evaporation – helped along by the ever-present wind. Most plants have must either reach deep for their moisture by means of long taproots or absorb moisture quickly at the surface through masses of fine roots.
The growing season on the tundra is short and unpredictable Six weeks are all the plants are allowed. In the north the season is even shorter but is partially compensated for by increased day length. The sun does not set until after 10:00 pm and it rises again around 3:00 am. The sky is completely dark for only a couple of hours in between.
Hail storm July 11th
Killing frost can come at any time. Open flowers are nipped but unopened buds survive. In some seasons successive frosts may prevent seed-set completely.
With conditions so sever that they seem to preclude life altogether one wonders how such a prolific and diverse flora is possible – yet the answer is obvious if we can recognize it.
The secrete is adaptation and it is the evolutionary adaptations that allow them to grow in this most difficult nitch that makes alpine plants so fascinating.
By mid-June most of the alpine tundra is free of snow. Thanks to winter winds the snow has been concentrated in depressions where drifts remain late into the summer. At the first hint of a warming spring sun the tundra explodes into bloom. We can enjoy the visual spectacle but few realize the urgency that prompts the coordinated flowering of dozens of species.
To cope with the short season the plants have adapted in numerous ways. Most plants are perennials – adding a little growth each season – and none at all in poor years. Perennials may take fifteen years to flower. Many plants are cold tolerant. Leaves begin photosynthesis and respiration and roots absorb nutrients at temperatures barely above freezing.
Heat, thought important, is not as critical for flowering as it is for seed development. Flowering must occur early to allow a maximum number of warm days for ripening of seed.
From eye level only a fraction of alpine species are noticeable and in fact miniaturization is the most common alpine adaptation. Tininess solves a number of problems for the plants. In a short season there is no time to grow large and small size reduces moisture requirements. Close to the ground friction reduces the speed of the wind so its detrimental effects are lessened. And it is warmer close to the ground where dark soil absorbs and holds heat. There is great beauty here in miniature.
A very obvious characteristic of alpine plants is hairiness. That so many plants have evolved hairs of various length and density at various stages of development and on various parts of the plant demonstrates that this adaptation must have great advantages.
Pedicularis lanata - Wooley Lousewort Erigeron humilis - Alpine Fleabane
It may seem contradictory but alpine plants actually need protection from the sun. The reduced atmosphere at high elevation allows intense ultraviolet radiation to reach the ground. Such radiation can be harmful to plant tissues. The sun itself shines with and intensity unknown at lower elevations.
Plant hairs absorb potentially harmful ultraviolet radiation and diffuse and soften direct sunlight.
Hairs contribute greatly to plant heating by reflecting visible light while absorbing heat – a kind of greenhouse effect. Hairs trap still air close to the plant, lessening the cooling and desiccating effect of wind.
Achieving cross-pollination is a serious problem for a majority of the plants. There are no honeybees in the alpine and bumblebees tend to be specialists – visiting only a few specially adapted plant species.
Butterflies are abundant and are important pollinators but low temperatures and constant strong winds keep them grounded much of the time.
Generally most plants must depend on flies for pollination. The flies in the alpine are able to maintain their activity despite the wind and cold. But flies are notoriously haphazard in their habits. Lacking the organized approached to pollination of honeybees, flies go from one flowering species to another wastefully mixing pollen among unrelated plants. Effective cross pollination seems to be achieved only by accident.
Nevertheless the widespread occurrence of saucer–shaped flowers which permits the unhindered movement of the flies, demonstrates the important role that flies have played in the evolution of these plants. The saucer-shaped flowers have adapted to the disorganized activities of the flies. By encouraging a maximum number of fly visits the plants achieve some certainty of pollination.
Another flower shape that is repeated by a number of tundra plants is the parabola. This shape focuses the meger warmth from the sun on the center of the flower. That slight elevation in temperature is enough to encourage pollinating flies to linger longer. Thus the chance of picking up an effective load of pollen is increased.