Warmer, wetter climate would impair California grasslands, 17-year experiment finds

September 5, 2016, Rice University
Grassland at Stanford University's Jasper Ridge Biological Preserve. An examination of 17 years of experimental data from the preserve is helping scientists from Rice University, Stanford and the Carnegie Institution for Science better understand how ecosystems will respond to climate change. Credit: Daniel J. Quinn/Stanford University

Results from one of the longest-running and most extensive experiments to examine how climate change will affect agricultural productivity show that California grasslands will become less productive if the temperature or precipitation increases substantially above average conditions from the past 40 years.

That's one conclusion from a new study in this week's Early Edition of the Proceedings of the National Academy of Sciences by researchers from Rice University, Stanford University and the Carnegie Institution for Science. The research team analyzed data from the Jasper Ridge Global Change Experiment, which has run continuously since 1998. The experiment simulates the effect of warmer temperatures, increased , increased nitrogen pollution and increased rainfall on a 1.8-acre tract at Stanford's Jasper Ridge Biological Preserve.

"There's been some hope that changing climate conditions would lead to increased productivity of grasses and other plants that draw down from the atmosphere," said study lead author Kai Zhu, a global ecologist and data scientist at Rice "In northern California, it was hypothesized that net grassland productivity might increase under the warmer, that are predicted by most long-term climate models. Our evidence disproves that idea."

The Jasper Ridge experiment involves 136 test plots where scientists can study how grass will grow under conditions that are predicted to occur later this century due to climate change. The experiment allows scientists to test four variables: higher temperatures, increased precipitation, increased atmospheric CO2 levels and increased nitrogen levels. The plots are configured in such a way that scientists can test each of the variables independently and in combination.

"Global change is quite complicated," said Zhu, who spent almost two years analyzing Jasper Ridge data during a postdoctoral fellowship at Stanford and the Carnegie Institution for Science from 2014 to 2016. "It does not just mean change in temperature. There are also changes in rainfall, atmospheric CO2, nitrogen and many other things. If we want to get a comprehensive understanding of everything, it is important to have experiments like Jasper Ridge, which manipulate more than one variable, both singly and in combination."

One clear finding from the data is that increased levels of CO2 did not increase grass production. Instead, the amount of grass grown at sites with elevated CO2 remained flat, even at CO2 levels almost twice the present atmospheric concentration.

"The nonresponse to CO2 is as important as any of our other findings," Zhu said. "That finding may surprise people because a lot have said that if you have more CO2 in the atmosphere, you'll get better growth because CO2 is a resource for plants. That's a popular hypothesis."

By examining data from all the test plots, including those where CO2 increased in conjunction with higher temperature, rainfall and nitrogen levels, and incorporating more than 40 years of climate records from the Jasper Ridge site, Zhu was able to deduce the optimal temperature and moisture levels for production under all conditions. His analysis showed that average conditions from the past 40 years are near optimal for grass production, and any significant deviation toward warmer or wetter conditions will cause the land to be less productive.

"Experiments like Jasper Ridge are designed to examine the interactive and unexpected effects that are likely to arise from global environmental change," said study co-author Chris Field, the founding director of the Carnegie Institution's Department of Global Ecology and the Melvin and Joan Lane Professor for Interdisciplinary Environmental Studies at Stanford University. "The nonlinear, interactive effects of temperature and precipitation on grassland primary production revealed by this analysis highlight the value of this experimental approach and suggest that it could be useful in studying how will affect other types of ecosystems."

Explore further: Ancient bones point to shifting grassland species as climate changes

More information: Nonlinear, interacting responses to climate limit grassland production under global change, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1606734113

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11 comments

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Shootist
3.1 / 5 (8) Sep 05, 2016
Sadly, trees will start growing.

SamB
2.3 / 5 (7) Sep 05, 2016
Sadly, trees will start growing.


Yes, sadly when the climate changes it seems only bad, sad things happen.
What are the odds?
BartV
2.6 / 5 (5) Sep 05, 2016
California grasslands are about as least productive areas as you can get. 9 months out of the year they are dry and brown. Doesn't look like a very good place to start experiments. But a wetter climate will surely help them become greener throughout the year.

Most of the places I know in the northern hemisphere are green in summer, brown in winter.

In California grasslands, they are green for 2-3 months in the winter, and dry and brown the reast of the year.

tblakely1357
2.3 / 5 (6) Sep 06, 2016
It is ironic that in the past religious types were preaching that doom is just around the corner and now it's environmentalists. This whole preaching doom thing seems innate in human nature. Oh well, religious tastes do change.
TheGhostofOtto1923
4.1 / 5 (9) Sep 06, 2016
Wouldn't grasslands yield to more tropical vegetation in a warmer wetter climate? And wouldn't a rainforest be more productive than grassland?
jeffensley
3 / 5 (2) Sep 06, 2016
Wouldn't grasslands yield to more tropical vegetation in a warmer wetter climate? And wouldn't a rainforest be more productive than grassland?


That would be the direction I would look. To suggest that an ecosystem would remain unchanged even if weather patterns consistently did is short-sighted. This study at best shows what will happen to grasslands prior to ecosystem adaptation.
gkam
1 / 5 (11) Sep 06, 2016
I live in the Bay Area. It is not forecast to be wetter here, only hotter.

And drier.
Windchaser
3.3 / 5 (7) Sep 06, 2016
It is ironic that in the past religious types were preaching that doom is just around the corner and now it's environmentalists. This whole preaching doom thing seems innate in human nature. Oh well, religious tastes do change.


Did you have any problem with the actual *research* that they did? Or is this just "I don't like it, so I'm going to ignore it"?

Your bias is showing.
TheGhostofOtto1923
3.9 / 5 (11) Sep 06, 2016
I live in the Bay Area. It is not forecast to be wetter here, only hotter.

And drier.
I live elsewhere and it is forecast to be different here too. But it didnt occur to me to mention it because Im not a flaming self-centered psychopath.
leetennant
5 / 5 (3) Sep 06, 2016
It is ironic that in the past religious types were preaching that doom is just around the corner and now it's environmentalists. This whole preaching doom thing seems innate in human nature. Oh well, religious tastes do change.


This is the equivalent of somebody arguing that doctors are "doom mongers" for saying you should stop smoking or you'll get cancer. Just flipping stop smoking and they'll stop talking about the cancer.

God the stupid - it burns.
ForFreeMinds
1 / 5 (2) Sep 11, 2016
"The experiment simulates the effect of warmer temperatures, increased atmospheric carbon dioxide, increased nitrogen pollution and increased rainfall on a 1.8-acre tract at Stanford's Jasper Ridge Biological Preserve. ... The [136] plots are configured in such a way that scientists can test each of the variables independently and in combination."

Seems the researchers aren't telling us much about how they simulated different climates on 136 different plots on 1.8 acres, because their methods likely don't simulate what they say they do. Are the plots physically and thermally isolated from each other including the atmosphere above them? I doubt it. Does the actual climate affect the simulated climate - I bet it does.

Just another study by some people looking to generate more government taking from others so it can be given to them for "research."

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