HARDINESS ZONES AND BIOCLIMATIC MODELLING OF PLANT SPECIES DISTRIBUTIONS IN NORTH AMERICA^©

The subject of potential species distributions has long been of interest to ecologists (e.g., Elton, 1927; Scott et al., 2002), but the subject is also important to agriculturalists, horticulturalists, and gardeners as it relates to plant hardiness. Plant hardiness is often thought of as the mortality or dieback of plants caused by temperature stress (mostly cold but also heat). In practical terms, hardiness zones are intended to help define the potential distribution of perennial plant species. The United States Department of Agriculture (USDA) extreme minimum temperature model (and related map) has been a useful surrogate for plant hardiness and is widely used throughout North America (; see also for a heat stress model).