Plants in Arctic Environments

Abstract

From a biological perspective, there is no universally accepted definition of the Arctic, but Arctic plants are generally considered to be those living in tundra and polar deserts beyond the northern climatic limits of forests, i.e., generally north of the boreal zone. The boundary between boreal forests and the Arctic is often broad and ambiguous. Arctic plants exist along a global continuum of decreasing floristic diversity with increasing latitude. This gradient starts well outside of the Arctic and continues within the Arctic to the northernmost reaches of land. Arctic plants come in a wide variety of forms. Mosses, lichens, and low-growing woody and herbaceous perennials characterize Arctic vegetation. Trees, succulents, ferns, and annual plants are rare or absent from most Arctic plant communities. Combinations of mosses, lichens, sedges, grasses, and dwarf woody shrubs dominate most Arctic tundra, and miniature flowering plants dominate the polar deserts. Adaptations of Arctic plants to cold and short growing seasons as well as other aspects of their physical environment are evident in their morphologies, physiologies, and life histories. Arctic plants are also adapted to their biotic environment. Extremely low temperatures are less characteristic of the Arctic than they are of some other regions, but the Arctic is consistently cold, resulting in permafrost and direct and indirect environmental challenges to plants. During short growing seasons Arctic plants utilize seasonally thawed soils above the permafrost and tolerate frozen soils in winter. Low temperatures affect the availability of mineral nutrients, frequently limiting the growth and productivity of Arctic plants. Usable soil is limited by permafrost, and low temperatures retard soil genesis, microbial activity, and uptake by roots. Birds and mammals play a key role in nutrient redistribution and the creation of local sites with high fertility. Arctic vegetation patterns are closely correlated with moisture and steep local moisture gradients are characteristic of the Arctic. Although the Arctic is climatologically a desert, few Arctic plants experience water stress. Moisture affects thermal characteristics and oxygenation of soils, which in turn affects decomposition rates and the availability of mineral nutrients. Patterns of moisture are strongly influenced by topography due to the combined effects of low precipitation, low evaporation, and water ponding due to permafrost. Mechanical stresses associated with freezing and thawing of soils and substrates shape the habitats of Arctic plants. Geomorphic processes unique to cold regions produce vegetational patterns and can lead to cyclic plant succession. The climate of the Arctic is dynamic, and changes in past plant communities have occurred on a wide variety of time scales. It is very difficult, if not impossible, to anticipate the effects of a changing climate on the Arctic due to the diversity of plants and habitats and due to nonlinear interactions between environmental factors within Arctic ecosystems.