Peripheral Plant Population Survival in Polar Regions

Abstract

All species have limits to their distribution and individuals that demarcate margins demonstrate an end-point in adaptation to a changing environment. Limits to plant survival arise either from a failure to grow or from an inability to reproduce. Consequently, matching climatic data with geographical distribution has to consider the biological causes for the failure of plants to survive outside any given area. Physical factors, such as thermal time (day-degrees) and growing season length, differentiate between the broadly recognised vegetation zones of High, Low, and Subarctic. However, within these zones the limitations to plant distribution are less readily related to climatic factors. In peripheral areas, relating physical climatic factors to species occurrence requires a knowledge of the many interactions between physiology and genetics of populations as they approach their territorial margins. Examination of the extent of variation found in plants growing in cold habitats reveals large differences both between and within populations and at different seasons in metabolic rates, temperature responsiveness and metabolic efficiency. The High Arctic represents a peripheral zone where conditions are prone to large fluctuations. Consequently, plant distribution will be affected by aspects of the environment that are not permanent, but which occur irregularly with varying frequency and intensity. This paper considers the physiological and genetic properties of polar plant populations that may facilitate persistence in uncertain and heterogeneous adverse environments. Particular attention is given to those species that appear to have maintained a presence at high latitudes since pre-Pleistocene times and have therefore survived many past environmental fluctuations.