Ecosystems Respond to Climate Change Differently as the Seasons Pass

Scientists studying the effect of drought and heat waves on grass growth have found that it matters when during the year these events take place, and that each month yields a different effect.

Scientists have found that U.S. midwest drought reduced prairie grass growth most in June.

“A major challenge in studying climate change is separating the effects of long-term trends from interannual variation,” says Saran Twombly, program director for the National Science Foundation’s (NSF) Konza Prairie Long-Term Ecological Research (LTER) Network.

“This study identifies variation in the timing and magnitude of drought and heat as keys to an ecosystem. The results highlight the importance of long-term data to understanding the complex interactions that underlie ecological responses to climate change.”

The research is based on 25 years worth of data taken from the LTER site in Kansas, one of 26 such sites across the planet.

The researchers found that droughts reduced grass growth most in early June, and that heat waves only reduced grass growth in late July. Neither droughts or heat waves had any impact whatsoever on grass growth during August or September.

“Future projections need to incorporate predictions of not only how much climate will change, but when during the year changes will happen,” says Joseph Craine of Kansas State University, the paper’s lead author.

“That the effects of climate change on grasslands depend on when they happen may not be much of a surprise–little snow in winter may have less effect than low rainfall in summer, for example.”

On the other hand, the sensitivity of grasslands to the timing of drought and heat waves was a big surprise.

“Heat waves mattering only during late July was not something we expected,” says Craine. “Everyone seemed to think that August heat waves and drought would have major effects on grass productivity, but we couldn’t find any.”

In fact, the effects of droughts and heat waves on grass growth declined over the summer season, rather than increasing.

“If these patterns are general across ecosystems,” the scientists write in their paper, “predictions of ecosystem response to climate change will have to account not only for the magnitude of climate variability but also for its timing.”

Source: National Science Foundation
Image Source: NSF Konza Prairie LTER Site

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