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Climate Change Boosts Then Quickly Stunts Plants, Decade-long Study Shows

Posted on 23 April 2012 by John Hartz

This is a reprint of a press release posted by the National Science Foundation (NSF) on April 10, 2012.

Global warming may initially make the grass greener, but not for long

Photos of ecosystems studied


Composite of the ecosystems studied, arranged left to right in order of increasing elevation.

Global warming may initially make the grass greener, but not for long, according to new research results.

The findings, published this week in the journal Nature Climate Change, show that plants may thrive in the early stages of a warming environment but then begin to deteriorate quickly.

"We were really surprised by the pattern, where the initial boost in growth just went away," said scientist Zhuoting Wu of Northern Arizona University (NAU), a lead author of the study. "As ecosystems adjusted, the responses changed."

Ecologists subjected four grassland ecosystems to simulated climate change during a decade-long study.

Plants grew more the first year in the global warming treatment, but this effect progressively diminished over the next nine years and finally disappeared.

The research shows the long-term effects of global warming on plant growth, on the plant species that make up a community, and on changes in how plants use or retain essential resources like nitrogen.

"The plants and animals around us repeatedly serve up surprises," said Saran Twombly, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research.

"These results show that we miss these surprises because we don't study natural communities over the right time scales. For plant communities in Arizona, it took researchers 10 years to find that responses of native plant communities to warmer temperatures were the opposite of those predicted."

The team transplanted four grassland ecosystems from a higher to lower elevation to simulate a future warmer environment, and coupled the warming with the range of predicted changes in precipitation--more, the same, or less.

The grasslands studied were typical of those found in northern Arizona along elevation gradients from the San Francisco Peaks down to the Great Basin Desert.

The researchers found that long-term warming resulted in loss of native species and encroachment of species typical of warmer environments, ultimately pushing the plant community toward less productive species.

The warmed grasslands also cycled nitrogen more rapidly. This should make more nitrogen available to plants, scientists believed, helping plants grow more. But instead much of the nitrogen was lost, converted to nitrogen gases in the atmosphere or leached out by rainfall washing through the soil.

Bruce Hungate, senior author of the paper and an ecologist at NAU, said the study challenges the expectation that warming will increase nitrogen availability and cause a sustained increase in plant productivity.

"Faster nitrogen turnover stimulated nitrogen losses, likely reducing the effect of warming on plant growth," Hungate said. "More generally, changes in species, changes in element cycles--these really make a difference. It's classic systems ecology: the initial responses elicit knock-on effects, which here came back to bite the plants. These ecosystem feedbacks are critical--you can't figure this out with plants grown in a greenhouse."

The findings caution against extrapolating from short-term results, or from experiments with plants grown under artificial conditions, where researchers can't measure the feedbacks from changes in the plant community and from nutrient cycles.

"The long-term perspective is key," said Hungate. "We were surprised, and I'm guessing there are more such surprises in store."

Co-authors of the paper include George Koch and Paul Dijkstra, both at NAU.

Source Paper:

Zhuoting Wu, Paul Dijkstra,George W. Koch,and Bruce A. Hungate, Biogeochemical and ecological feedbacks in grassland responses to warming, Nature Climate Change(2012) doi:10.1038/nclimate1486

Received 01 June 2011 Accepted 08 March 2012 Published online 08 April 2012

Click here to access the Abstract. 

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Comments

Comments 1 to 7:

  1. But, but...: CO2 is plant food! ;-)

    (I suspect we'll be told, a priori, that that will overwhelm any negative effect from the rise in temperatures. It's hard to see how you could test it in such a field study.)

    Thanks for the article. That's a pretty ingenious method. I will note, though, that 30cm diameter cores are rather small - very much all edge-effect - and even when measuring against the controls transplanted at the original altitude (and assuming associated transplant shock is equal - unlikely, surely?) I can't help but think that they're at a significant disadvantage relative to the locals in the new, warmer territory.

    Any discussion of this is behind the paywall, however...

    The duration of study warning is duly noted.
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    • The team transplanted four grassland ecosystems from a higher to lower elevation to simulate a future warmer environment, and coupled the warming with the range of predicted changes in precipitation--more, the same, or less.

      The grasslands studied were typical of those found in northern Arizona along elevation gradients from the San Francisco Peaks down to the Great Basin Desert.

      The researchers found that long-term warming resulted in loss of native species and encroachment of species typical of warmer environments, ultimately pushing the plant community toward less productive species.

    So the team transplanted a climax ecosystem to a lower vegitation zone and were suprised that the climax ecosystem in that lower vegitation zone eventually prevailed.
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  2. You've got the right quote but missed the important point: The encroaching species which overtook the transplanted species were less productive, and yet still managed to overtake the transplanted species.

    The effect of the simulated warming was a shift toward less productive species, and therefore a reduction in CO2 uptake. That is the part which was surprising.
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  3. So Steve reads part of a post, finds the parts which support his preconceptions and ignores the rest. How unsurprising.
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  4. Suggested reading:

    Global warming: Alpine plants swiftly losing ground” by Bob Berwyn, Summit County Citizens Voice, Apr 22, 2012

    http://www.skepticalscience.com/admin_author.php?Action=EditBlog
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  5. In this article it seems they are talking about an increase in temperature that then remains at this level. This results in faster growth rate at first but then diminished growth over the years. There is a somewhat related phenomenon which is well known for plants and animals. They grow faster and faster as the temperature is increased but the lethal temperature is only a degree or two above the temperature of maximum growth. At first thought you might expect a bell shaped growth curve. However it is only like a bell curve on the left (colder) side. It is a cliff on the warmer side.
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  6. Having given the paper a quick read, I'm surprised there is no measure of CO2 included at both sites. My understanding is that CO2 partial pressure decreases with increasing altitude (roughly 10% less CO2 per 1000m), thus transplanting from high to low sites would also impose a CO2 enrichment effect.

    It is also my understanding that CO2 enrichment causes a short term boost in plant productivity which is then lost as other factors become rate limiting (photosynthetic acclimation). This sounds familiar to the findings in this paper, although I am unsure on the time-frames on CO2 photosynthetic acclimation.
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