The majority of the conversation about global or regional temperature involves discussion about how the average annual or monthly temperature has changed over time. However, for many organisms it is actually the range of temperatures they experience throughout the day (the diurnal temperature cycle or DTC) and throughout the year (the annual temperature cycle or ATC) that is most important in terms of biological processes, phenology, and other ecological interactions. Think, for example, about any forest pest that is a concern in your region – chances are its population is significantly affected by the magnitude of temperature ranges from summer to winter and from night to day. In this bulletin, we will explore this topic further and highlight a recent analysis that sheds new light on global temperature trends during the period 1975-2013.
The observed changes in the range of daily and annual temperatures will have important consequences for many species. In particular, short-lived organisms, such as the mountain pine beetle, have already benefited from increased winter temperatures that have allowed their populations to increase. Organisms adapted to a larger range of temperatures may fare better under conditions where the DTC is increasing, as opposed to more specialized organisms that can only survive or reproduce within a narrow temperature range. Also, in places where the daily and annual temperature ranges are becoming more similar (as they are in the tropics), we may see seasonal organisms that can now persist throughout the year. The most immediate concern for forest managers will be the effect of these changes on the life cycle and population dynamics of various pests and diseases.
The charts, data, and results are discussed in detail in the source article.