July 8, 2008 -- One of the longest-running experiments to predict the effects of climate change on plants offers some good news: After more than 13 seasons of applying typical global warming influences, a grassland ecosystem showed very little change.
Neither increased winter temperatures nor higher rates of summer rainfall (two predicted conditions of global warming) seemed to have any marked effect on the grasslands.
Only the simulation of ongoing summer drought caused an appreciable change in the amount of growth and the composition of plants in the 10-foot-square test areas of grassland.
"The magnitude of the treatments is about the same as inter-annual climate fluctuations," said author Jason Fridley of Syracuse University in N.Y. "The way the communities change from year to year, with some becoming more abundant and some less abundant, is more than what's seen over 13 years."
The site, a grassland typically used for grazing in northern England, was part of an experiment started in 1993, in which researchers manipulated two sites -- one on the north and one in the south of England -- by applying heat or changing the amount of rainfall that hit the sites to see how they responded to conditions expected under climate change.
The researchers simulated typical grazing by clipping plants short. They simulated drought by creating by rain-detecting covers that diverted rainfall off of the plots.
The site in the south changed dramatically over the initial five-year period, Fridley said, while the northern site stayed pretty much the same.
"The southern site was essentially dismantled," Fridley said. "My collaborator Philip Grime, said, 'Gosh, that's ridiculous. Individuals of these plants live for decades.'"
So, Grime, now retired from the University of Sheffield near the northern site, continued to track that site.
"He had to take a bus out there an hour one way," Fridley said. "He kind of kept going by hook or by crook."
The researchers believe that the very low levels of nutrients in the soil at the Sheffield site is one of the key factors behind the ecosystem's stability.
"All of the nutrients are in the biomass of the plants," Fridley said. "Unless the climate is severe enough to kill many of these, there are no new nutrients in the soil. Even if you have a seed from the south coming up, if there are no nutrients, it's not going to do anything."
The soils at the southern site were much more nutrient-rich, Fridley said.
Other climate manipulation experiments have shown similar reactions. John Harte of the University of California, Berkeley, has been heating patches of meadow in the Rocky Mountains for just longer than at the British sites.
"One of the things we've found in our site is that the grasses and sedges [plants similar to grasses], which accounted for 20 percent of the cover, showed no response at all," Harte said. "So in a sense there is consistency."
In both places, grasses were resistant to change.
Now the researchers are looking at individual plants to see if they have adapted to the changing climate, even though the overall species composition hasn't changed.
"One way of viewing this paper is that we have been looking at the wrong level the whole time," Fridley said. "We've been looking at species, but maybe we should be looking at individuals. Some may not have deep roots. Some may have deeper roots. Is natural selection occurring locally? We have some evidence that that's the case."
Understanding why the sites changed or didn't is more important than how they changed, Harte explained.
"It's not so important that this changed and this didn't," he said, "but it's the mechanisms underlying the changes that are important because those can be extrapolated to other situations."
Related Links:
Jessica Marshall's blog: EnvironMental Case
How Stuff Works: The Effects of Climate Change
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