Arctic and Alpine tundra environments Flora and fauna

Arctic and Alpine tundra environments Flora and fauna

The biotic environment

Vegetation Plants that have adapted to live in very cold conditions, including changes in cell structures when the temperature falls below freezing, are called hekistotherms. Many plants also have to adapt to wet conditions, i. e. the bogs and muskegs of Northern Canada and Siberia. These plants are hygrophytes, e. g. cotton grass or sedge. Those plants which have to make do without much water because it is either frozen or there are sandy conditions are xerophytes. In these plants small leaves limit the amount of water lost through transpiration.

Therophytes are annual plants which regenerate from seed. These are absent. Cryptophytes are adapted to extremes of heat or cold and persist because they regenerate from buds, bulbs or rhizomes that are completely buried in the soil. Hemicryptophytes are typical of moist temperate regions. They die back at the end of the growing season and buds are protected by the withered leaves and soil. Chamaephytes include small shrubs and herbs that grow close to the ground. Snow offers some protection during cold winter months. Phanerophytes are trees and small shrubs. They carry buds on the tips of branches. They are characteristic of hot or mild moist environments where plants are not subject to drought or frost. Types of plants found in the tundra

Rhizomes A usually elongate and branched modified plant stem which grows horizontally, below or on the surface of the soil, often appears enlarged by food storage. Roots, buds and leaves then emerges at different point from the nodes. Rhizomes are creeping thickened stem (not a root) differ from other storage structures (like: tuber, bulbs, etc. ) by growing horizontally partially or entirely under the surface of the ground, consisting of a series of nodes with roots. The primary growing point is at one end of the rhizome; additional growing points form along its sides from the nodes.

Bloom plants In the short Arctic summer the tundra becomes a mass of colour. Arctic poppies, gentians and saxifrage are typical species. Crowberry (Empetrum nigrum) above Arctic foxglove below Cotton grass (Eriophorum angustifolium) on wetter ground

Anthocyany Many of the flowers found both in the Arctic tundra and in the Alpine tundra are coloured purple. In this way they can absorb more of the Sun’s energy and grow more quickly. Such Alpine plants as the gentian, saxifrage and that on the right Hedysarum hedysaroides all show bright purples. In the Arctic tundra many of the heathers (Calluna) and foxglove species have similar colours. Such plants are termed anthocyanic. Many flowers such as arctic avens (Dryas integrifolia) and arctic poppy (Papaver radicatum) have bowl shaped flowers which act as parabolic reflectors warming the plant. They are also heliotropic and turn to face the sun as it moves overhead.

Pollination is chiefly achieved through the help of insects, of which bees and the ubiquitous mosquito are most important.

Dwarf Birch (Betula nana) A shrub layer of dwarf willows and birches develops where the active layer is slightly deeper. Usually they grow to heights of 40 – 60 cm, but can reach 2 – 5 m on banks of rivers where a deep snowpack accumulates protecting the plant in the winter.

A much more diverse collection of plants occur in Alpine tundra environments, partially due to a wider variety of habitat. Crowberry (Empetrum nigrum) is dominant at altitudes of 1600 – 2400 m. Alpine grasslands are present in wetter areas, with Alpine meadow grass (Poa arctica) and mat grass (Nardus stricta) being very common. They have long been used for summer grazing. The grasses often form tussocks and the dead grass helps protect the living stalks. Cushion plants such as musky saxifrage (Saxifraga exerata) and Swiss rock jasmine (Androsace helvetica) grow on ledges and in crevices where there is more protection from grazing and the weather. Some Alpine plants are still to be found in Snowdonia, e. g. Snowdon lily (Lloydia serotina). Alpine mountain flora

Alpine meadow grass (Poa arctica)

Fauna

Lemmings In the Arctic lemmings are the most important species in terms of herbivory and the subsequent transfer of energy to higher consumers. They feed on grasses and sedges in summer, but may include moss in winter. Every 3 – 6 years the lemming population increases sharply. Similar fluctuations occur in other rodent populations in the Arctic, with corresponding oscillations in predator species. As lemmings consume the available food the population crashes. Heavily grazed areas have higher soil temperatures, which stimulates decomposers to release more nutrients from dead plant and animal tissue. Vegetation recovers enabling the breeding success of lemmings to improve. They reproduce 2 -4 times per year with 4 -6 young per litter. This consumes the available food supply and starvation sets in with a further population crash.

Large herbivores of Arctic tundra Above left and right, reindeer – found in N Europe and Siberia Below left, caribou – the N American equivalent Below right, musk ox

Large herbivores of Alpine tundra areas Above left – the chamois of the Alps Below left – the tahr of the Himalayas Above right – the llama of South America Below right – the yak of the Himalayas

Carnivores of the tundra Carnivores are adapted to the harsh conditions with thick coats and a hibernation period. Arctic fox and wolf The importance of lemmings is reflected in similar oscillations of many predator species. Brown bear and polar bear