Biol. Rev. zyxwvuts (1968), 43, pp. 481-529 zyxwvuts THE ECOLOGY OF ARCTIC AND ALPINE PLANTS BY W. D. BILLINGS zyxwv AND H. A. MOONEY Duke University, Durham, North Carolina, and Stanford University, Stanford, California, zyxwv U.S.A. (Received I zyxwvu 5 May I 968) CONTENTS I. Introduction zyxwvuts . . . . . . . . . . . . 481 484 (I) Present and past distributions of tundras . . . . . . 484 zy (2) Environmental characteristics . . . . . . . . 485 (3) Vegetational characteristics . . . . . . . . 489 11. Geographic extent and general characteristicsof arctic and alpine vegetation 111. Adaptations of plants to arctic and alpine environments . . , . (2) Physiological ecology of the life-cycle in arctic and alpine vascular plants Seedling establishment . . . . . . . . . (I) Life forms and general morphology . . . . . . . Seed dormancy and germination . . . . . . . Chlorophylls and other pigments . . . . . . . Photosynthesis and respiration . . . . . . . . . . . . . Annual cycle of growth . . . . . . . . . IV. Primary productivity . . . . . . . . . . . Effects of water availability and use V. Summary . . . . . . . . . . . . . 522 VI. References. . . . . . . . . . . . . 524 I. INTRODUCTION Among the earth's terrestrial environments, none has less biologically usable heat or has fewer kinds of adapted plants than the tundras and barrens above and beyond the alpine and arctic timberlines. Here, plant phenotypes are environmentally selected by a climatic severity unknown in the mild, moist tropical environments where vascular plants originated and remain in such variety today. Nor does so severe a selection operate in temperate regions where warm summers help to compensate for cold winters by supplying a season of tropical heat to the metabolic activities of plants emerging from dormancy. Only a few kinds of phenotypes have passed this low-temperature screening successfully and have added their gene-enzyme systems to the floras and vegetations of polar and alpine regions. It is the purpose of this review to bring together in brief form the principal facts and theories concerning plant adaptations to these cold environments. In short space, we cannot improve on the detailed coverage of certain aspects of plant adaptation to arctic or alpine conditions provided by Holm (1922), Schroeter (1926), Sarensen (1941), Pisek (1960), Tikhomirov (1963), Bliss (1962b), Tranquillini (1964), and others. Here, we shall attempt to bring such information up to date and to discuss the problems of physiological adaptation to low-temperature environments.