Projected changes in risks of winter damage to fruit trees and plant hardiness zones in Canada

Winter climate conditions, especially extremely low temperatures, constrain the production of fruit trees and other perennial crop species in Canada. Significant decreases in cold extremes under climate change may result in changes in plant hardiness zones and the distribution of crop species across the country. Climate warming might also bring changes to climate conditions that affect fall hardening, loss of cold hardiness due to winter thaws, and spring frost damages. Using the most up-to-date climate projections, we provide projected changes in the risks of damages to fruit trees during winter based on five agroclimatic indices and changes to the United States Department of Agriculture (USDA) plant hardiness zones based on long-term averages of annual extreme minimum air temperatures in the near-term (2030s, 2020–2049), mid-term (2050s, 2040–2069), and distant future (2070s, 2060–2089). Our results suggest that climate change might be beneficial for fruit trees across Canada with (1) improved fall hardening because of more time to acquire cold hardiness due to delayed first fall frost and (2) decreased winter coldness with increases in annual minimal temperatures and decreases in the accumulation of cold degree-days below –15 °C. The risks of loss of cold hardiness due to winter thaws will increase slightly while the risks of spring frost damages to buds will be largely unchanged. Under a warmer distant future, the USDA plant hardiness zones across Canada would increase by 1.5–2 “full” zones, which may lead to the introduction of new fruit tree species and opportunities for Canadian producers.