Topography and geological history

This book considers the biology of bryophytes and lichens in polar tundra and adjacent, open woodland, their contribution to the vegetation, their role in polar ecosystems, and their adaptations to the rigours of life in regions generally regarded as among the least hospitable on earth. Tundra is used here in the broad sense of treeless regions beyond climatic timberlines. It occurs in the polar regions as defined in Figs. 1.1 and 1.2, and in some alpine and oceanic areas at lower latitudes.

The polar regions are diverse in topography and climate. Arctic lands comprise substantial parts of the North American and Eurasian continents which, with Greenland and smaller islands, encircle a polar ocean (Fig. 1.1). The terrain ranges from extensive flat-bedded plains and plateaus to folded mountains, often high and imposing as in the Brooks Range, Alaska, where elevations reach over 2800 m (Figs. 1.3 and 1.4). Except in Greenland, contemporary glaciation is localised, and largely confined to Spitzbergen and other far-northern islands. In contrast, the Antarctic continent is centred over the pole and is surrounded by the vast expanse of the Southern Ocean, with a minimum width of over 850 km between the Antarctic Peninsula and Cape Horn (Fig. 1.2). The continent is fringed by coastal mountains, and rises to an inland ice-plateau at elevations of 1800 to 3800 m. Over 98% is currently buried beneath an ice sheet more than 4 km thick in places. Islands lying close by the mainland or widely scattered in the Southern Ocean thus provide the major terrestrial habitats in Antarctic regions, where vegetation is restricted to the almost universally rugged terrain of coastal regions.