Time of Year Important in Projections of Climate Change Effects on Ecosystems

Scientists have found that U.S. Midwest drought reduced prairie grass growth most in June.: Photograph courtesy of NSF Konza Prairie LTER Site

Results of study on prairie grasslands show differences across the months.

Does it matter whether long periods of hot weather, such as last year's heat wave that gripped the U.S. Midwest, happen in June or July, August or September?

NSF's 26 LTER sites circle the globe and stretch from pole to pole.: Photograph courtesy of NSF LTER Network OfficeScientists studying the subtle effects of heat waves and droughts say that when such events happen makes a big difference.

Based on more than 25 years of data from the National Science Foundation (NSF) Konza Prairie Long-Term Ecological Research (LTER) site in Kansas--one of 26 such NSF LTER sites across the globe--ecologists looked at how droughts and heat waves affect grass growth during different months of the year.

The journal Proceedings of the National Academy of Sciences (PNAS) published their results on 13 February 2012.

"A major challenge in studying climate change is separating the effects of long-term trends from interannual variation," says Saran Twombly, program director for NSF's 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 researchers found that droughts reduced grass growth most in early June, while heat waves reduced grass growth only during late July.

Drought or heat waves seemed to have less effect on grass growth as summer turned to fall.: Photograph courtesy of NSF Konza Prairie LTER Site

Neither drought nor heat waves in August or September seemed to have an effect on grass growth.

"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.

Co-authors of the paper are Jesse Nippert, Adam Skibbe and Stacy Hutchinson of Kansas State University; Andrew Elmore of the Appalachian Laboratory, University of Maryland Center for Environmental Science; and Nathaniel Brunsell of the University of Kansas.

"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," Craine says.

For some grasses, flowering is altered by drought in May, for others, drought in August.: Photograph courtesy of NSF Konza Prairie LTER Site

The sensitivity of grasslands to the timing of drought and heat waves was a big surprise, however.

"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."

The effects of drought and heat waves in fact declined over the summer season.

Other studies showed that drought and heat waves affect parts of ecosystems differently.

"For example, in some grass species, flowering is altered by drought in May, and in others by drought in August," Craine says.

Bison on the prairie may gain more weight in years when droughts come in June or July.: Photograph courtesy of NSF Konza Prairie LTER Site

Bison that graze the prairie don't seem to respond to heat waves, but may gain more weight in years with drier weather--provided that droughts come in late June or early July rather than in August or later.

Fire is a natural part of a prairie ecosystem, including at NSF's Konza Prairie LTER site.: Photograph courtesy of NSF Konza Prairie LTER Site

The researchers are looking at long-term records from other LTER sites to determine whether there's uniformity to the Konza findings.

"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."

For now, says Craine, "the results will change the types of questions we ask about climate and ecosystems."

This news is from the National Science Foundation (NSF) 13 February 2012

Notes:

Related Websites:

NSF Konza Prairie LTER Site: http://www.lternet.edu/sites/knz/
NSF LTER Network: http://www.lternet.edu
NSF Forum: The Challenge of a Sustainable Future: Long-Term Ecological Research Offers New Answers: http://www.nsf.gov/news/news_summ.jsp?cntn_id=123081

Related coverage:

Chapters in new book “Water and Sanitation Related Diseases and the Environment: Challenges, Interventions, and Preventive Measures,” a Wiley-Blackwell collaboration with Horizon International which was released in November 2011:

“Ecosystem Services, Water Resource Development, and Human Infectious Disease,” Uriel N. Safriel, United Nations Convention to Combat Desertification and Department of Evolution, Systematics and Ecology, Institute of Life Sciences, Hebrew University of Jerusalem

“Changing Geographic Distribution of Disease Vectors,” Mary Wilson, M.D., Associate Professor in the Department of Global Health and Population, Harvard School of Public Health, Associate Clinical Professor of Medicine, Harvard Medical School