The surprising sensitivity of ecosystem structure and function to winter climate anomalies

Background/Question/Methods

The study of ecosystem-climate relationships has focused almost exclusively on climatic change during the growing season or used annual averages that homogenize climatic variation across seasons. This research pattern disproportionately neglects ecosystem changes during the cold season when animals and plants are often behaviorally dormant, yet many important metabolic and physical processes still occur. Indeed, ecosystem responses to climate anomalies during the winter can be equal or greater than responses to growing season variation. Additionally, knowledge regarding ecosystem response to winter is ecosystem biased, apparent by the limited number of “winter ecology” studies in non-alpine/arctic sites. Understanding the sensitivity of ecosystem properties to winter climate anomalies is a timely and important endeavor, as winter climate is changing faster than summer temperatures in many regions. To uniformly examine how winter anomalies have influenced properties within a wide variety of ecosystems, we used unique long-term data-sets of ecosystem structure and function, and a newly developed analytical and statistical approach (Critical Climate Period) to identify the period(s) of the year that have the strongest correlation between climate and metrics of ecosystem structure and/or function. Specifically, the influence of winter climate anomalies on ecosystem properties was examined across 10 long-term ecological research (LTER) sites.

Results/Conclusions

Sites represented a diverse array of environments, including grasslands, tundra, desert, forest and agricultural fields. Main ecosystem properties included stream chemistry and plant community measures (ANPP, species richness, phenology). Plant communities at half the sites were significantly influenced by winter climate. For example, ANPP and winter precipitation were negatively correlated in agricultural fields of Michigan, positively correlated in Chihuahuan deserts of New Mexico, and unrelated in tallgrass prairies of Kansas. Timing of influential precipitation during winter also varied, and any winter precipitation influenced spring NPP of semiarid grasslands, but only precipitation during the final days of winter decreased NPP of midwestern prairie. The influence of winter climate often related to limiting factors for each ecosystem. For example, fluctuations in winter precipitation had large impacts in water-limited desert grasslands, while changes in winter temperature had a greater impact on systems with a prominent cold dormant season. Mechanistic observational and experimental studies at each ecosystem were key in determining whether generated Critical Climate Periods (CCPs) were valid and had an ecological explanation therefore representatives from each site collectively interpreted the data. Based on this research, winter climate and ecology should be taken into account when evaluating the impacts of changing climates.