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A lichen consists of a specific alga and a specific fungus in a symbiotic relationship that makes them act as a single plant. Typical pioneers on bare rock, lichens are able to absorb water and nutrients directly into the cells of their foliage and have no roots, i.e., no vascular system. Lichens take different forms: crustose (crust-like), foliose (leaf-like), and fruticose (stalk-like). A characteristic lichen of the tundra is the fruticose reindeer lichen (often miscalled reindeer moss) shown below. Reindeer lichen is an important food item for many Arctic herbivores.
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Sedges are members of the flowering plant family, Cyperacaeae. In the Arctic, two important genera are Carex and Eriophorum. One of the indicator species of the tundra, the so-called cotton grass, is actually a sedge of the genus Eriophorum.
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| Carex sp. | Cottongrass (Eriophorum sp.) |
Perennial forbs spend the cold dark winters in a dormant stage. The foliage dies down to ground level or disappears completely; the growth buds are protected below ground. During the short growing season in the Arctic, energy is stored in underground structures such as bulbs. When warmth returns to the high latitudes, the plant is ready to grow quickly from its energy reserves and, in good years, flower and set seed in the few weeks when temperatures are above 50° F and daylight lasts 24 hours.
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Woody shrubs of the tundra are often dwarfed and only a few inches in stature. The stems of the willow shown below are prostrate and sheltered from the cold and wind by a cover of dead and living non-woody plants. In the photo below only the flower of the willow protrudes above its protective cover.
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The heath or heather family (Ericaceae) contains an array of species, many with hard, evergreen leaves able to withstand drying winds and cold temperatures. Among those which may be familiar to you are rhododendron, blueberry, and cranberry. Pictured below is a characteristic heath of the tundra, Labrador tea. This tiny shrub stands only 2-3 inches tall.
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Below is another member of the heath family, one which clearly shows the characteristics of a mat or cushion plant growthform. This is the alpine azalea, Loiseleuria procumbens. The mat or cushion consists of many individual plants tightly clumped together. Those on the outer edge may suffer damage and death from cold and drought, but the individuals at the center survive to perpetuate the species.
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A rosette, a concentric ring of leaves around a central bud, is a growth form that is adaptive to several kinds of severe environment. On the tundra, the shape of the plant serves to protect the fragile growth bud from cold winds. It may also serve to trap insulating snow in winter and dew during the dry growing season. The rosette plant in the photograph below also shows a mat-forming tendency. Winter die-off of parts of the plant still leave the overwintering bud protected.
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Patterned ground consists of polygons formed of large pebbles and cobbles and other coarse rock fragments with fine particles concentrated on the inside. The sorting of the substrate according to particle size is believed to the expansion of pockets of water as they freeze each autumn. The center tends to rise as ice forms and larger fragments tumble to the outer edge, finer particles adhere to the center. The result as far as plants and animals are concerned are alternating microhabitats: boggy areas in the centers of the polygons and drier, sun-warmed rocks on the margins.
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On south-facing slopes near the Bering Sea in Alaska can be seen outliers of the boreal forest. Warmed by the summer sun, depth to permafrost is greater on these slopes than elsewhere in the region and there is enough unconsolidated material to allow the roots spruce and fir to gain a foothold. The affect of differing temperatures on slopes facing in different directions allows this region to be an ecotone between the tundra and the boreal forest.
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