Global study reveals extreme impacts of drought on grasslands and shrubs

A global study organized and led by scientists at Colorado State University shows that the effects of extreme droughts, expected to increase in frequency with climate change, have been largely underestimated on grasslands and shrublands.

The results, published in Proceedings of the National Academy of Sciences—quantify the impact of extreme short-term drought on grassland and scrubland ecosystems across six continents with a level of detail not previously possible.

This is the first time such a large experiment has been undertaken to generate a baseline understanding of potential plant productivity losses in these vital ecosystems.

Melinda Smith, a professor in the CSU Department of Biology, led the study and is first author of the paper. She said the observed reduction in a key carbon cycle process after a single drought event occurring every 100 years far exceeds previously reported losses for grasslands and shrublands.

“We were able to determine that loss of air plant growth – a key measure of ecosystem functioning – was 60% higher when short-term drought was extreme, compared to less severe droughts that were more frequently experienced in the past,” she said. “Previous studies suffered from methodological differences when estimating the impacts of extreme drought on natural ecosystems, but our standardized, distributed approach resolved this issue.”

Smith added that the project also highlights the variability of drought response in grassland and scrubland ecosystems, providing both an examination of the global impacts of climate change as well as insight into which areas will be most affected. stressed or most resilient in the years to come.

Global data collection on extreme droughts on grassland and scrub ecosystems

Known as the International Drought Experiment, the newly published research dates back to 2013 as part of the National Science Foundation’s Drought-Net research coordination network. In total, more than 170 authors representing institutions around the world are cited in the new PNAS study carried out over the last four years.

To gather their data, the researchers built precipitation manipulation structures to experimentally reduce the amount of natural precipitation available to ecosystems for at least one full growing season. About half of the participating sites imposed extreme drought conditions on these structures, while the remainder imposed less severe drought for comparison.

As Earth’s climate continues to change, short-term droughts of statistically extreme intensity will become more frequent, and what was once thought to be a 100-year drought would now potentially occur every two to five years, a Smith said. But due to the historical rarity of extreme droughts, researchers have been unable to estimate the true extent of their ecological consequences.

Smith said grasslands and shrublands were perfect test areas to fill this research gap because they are easier to manipulate for study than other systems, such as forests. They also store more than 30% of the world’s carbon stock and support key industries such as livestock farming.

“These are key ecosystems that span globally, which makes them very relevant to this type of work,” said Smith, who also chairs the faculty council on campus. “Grasslands and shrublands cover between 30 and 40 percent of the planet and frequently experience precipitation deficits. This means they are more vulnerable to climate change.”

Results from the sites also provide insight into how specific climate, soil and vegetation types broadly influence drought response. Although the work shows that drier, less diverse sites like those in Colorado are likely to be most vulnerable to extremes, Smith said drought severity is the most consistent and important factor in determining the response of an ecosystem.

“Our data suggests greater losses in drier sites, but if you reach the extremes – which is expected – we can generally expect substantial losses no matter where you are in the world,” he said. she declared. “We also found that even moderate losses from less severe droughts would likely result in significant impacts on populations that rely on these systems. And then there is a combined loss of function across the world to consider as well. “

Smith said the team was currently reviewing data collected over the full four years of the project to now assess multi-year drought impacts on a global scale.