Climate Fact: Phenology, Adaptation and Climate
In Brief: Different plants use different signals to tell them when to come out of winter dormancy, which affects their response to climate change.
Phenology is the study of naturally recurring events, such as plants blooming in spring. In moist temperate regions like the Eastern United States, some plants come out of their winter dormancy once temperatures become sufficiently warm – which is usually once there is a certain number of cumulative hours with ambient (air) temperatures above a certain threshold (such as 50 hours over 50 degrees Fahrenheit during a ten day period). Other plants will only respond to a temperature signal once there has been a certain number of winter “chill hours,” or a set amount of hours during the cold season when temperature are near or below freezing. Other plants unleash their flowers and leaves when the days become a certain length – such plants are said to be “photoperiod controlled.” Depending only on temperature as an “alarm clock” is risky for a plant. This is particularly true in regions with variable weather regimes, where the transition from winter to spring can mean several days of temperatures in the 60s that are soon followed by a cold front and a few days of freezing temperatures, which can potentially damage a plant’s young leaves or flowers. Photoperiod and chill hour “alarm clocks” keep plants from sprouting their sensitive leaves and flowers at the wrong time. Because different plants use different “alarm clocks,” not all species respond to warming temperatures in the same way. Most plants and animals do appear to be responding to warming temperatures, with most species at temperate latitudes advancing their spring activities by 2.5 days per decade since 1970.
Season: Spring
Sources: Korner, C and Basler, D. “Phenology under global warming.” Science 19 (2010): 1461-1462 and Menzel, A et al. “European phenological response to climate change matches the warming pattern.” Global Change Biology 12 (2006): 1969-1976.
