North American forests unlikely to save us from climate change, study finds

July 20, 2016
A sub-alpine forest in Colorado. Forests in the southwestern US are expected to be among the hardest-hit, according to the projections resulting from the study. Credit: Sydne Record

Forests take up 25-30 percent of human-caused emissions of carbon dioxide—a strong greenhouse gas—and are therefore considered to play a crucial role in mitigating the speed and magnitude of climate change. However, a new study that combines future climate model projections, historic tree-ring records across the entire continent of North America, and how the growth rates of trees may respond to a higher concentration of carbon dioxide in the atmosphere has shown that the mitigation effect of forests will likely be much smaller in the future than previously suggested.

Published in the journal Ecology Letters, the study is the first to reveal the possible impact of a changing climate on the growth rate of trees across all of North America, in other words, how their growth changes over time and in response to shifting environmental conditions. The result are detailed forecast maps for the entire North American continent that reveal how will be impacted by climate change.

The research team, led by scientists at the University of Arizona in Tucson, combined climate projections for North America developed by the International Panel for Climate Change (IPCC) with historic tree-ring records based on samples covering the period 1900 to 1950 at 1,457 sampling sites across the continent.

"We then looked at how the growth of those trees changed historically under various past climates and used that to predict how they will grow in the future across the continent all the way from Mexico to Alaska," said the study's first author, Noah Charney, a postdoctoral research associate in UA's Department of Ecology and Evolutionary Biology.

"The research is unprecedented and novel in the use of big biological data," said co-author Brian Enquist, a professor in the UA's Department of Ecology and Evolutionary Biology and a fellow of the Aspen Center for Environmental Studies in Aspen, Colorado. "We utilized a network of more than two million tree-ring observations spanning North America. Tree-rings provide a record into how trees that grow in different climates respond to changes in temperature and rainfall."

The study calls into question previous conclusions about how forests will respond to warmer average temperatures, increased greenhouse gas emissions, and shifting rainfall patterns.

Projected change in forest growth rates for the second half of this century. With the exception of coastal areas, growth rates are projected to go down throughout the North American continent. Credit: Noah Charney

The team was startled to find no evidence for a greenhouse-gas absorbing process called the boreal greening effect in their simulations. Boreal greening refers to the assumption that trees in high latitudes, where colder temperatures limit growth, should benefit from warmer temperatures and higher concentrations of in the atmosphere and, as a result, "green" under the effects of climate change. In turn, these thriving boreal forests should be able to scrub more carbon dioxide from the atmosphere, so goes the idea, dampening climate change.

"Until now, there wasn't a good way to take into account how trees respond to climate change under novel climate conditions," added senior author Margaret Evans, an assistant research professor in the UA's Laboratory of Tree-Ring Research (LTRR) and the UA's Department of Ecology and Evolutionary Biology. "Our study provides that perspective. We see that as trees are pushed under the effect of , their response changes."

"Many previous climate modeling studies counted on the boreal forests to save us from the climatic disaster by offsetting our emissions, but we don't' see any greening in our results," said Valerie Trouet, an associate professor in the LTRR. "Instead, we see browning. The positive influence warmer temperatures are believed to have on boreal forests—we don't see that at all."

The most dramatic changes in projected forest growth rates were found in the interior West of the North American continent, with up to 75 percent slower growth projected for trees in the southwestern U.S., along the Rockies, through interior Canada and Alaska. Increases in growth were seen only along certain coastal areas, mostly in the Pacific Northwest, Northeastern Quebec and the Maritime Provinces and the Florida panhandle.

Some of the predictions arising from the simulations are already happening, the team found.

"In Alaska, for example, where trees have been projected to respond positively to warming temperatures under the boreal greening effect, we see that trees are now responding negatively instead," Evans said. "Trees in very high latitudes are limited by cold temperatures, so yes, in warmer years they grow more, but there is a tipping point, and once they go past that, a warmer climate becomes a bad thing instead of a good thing."

A deciduous Forest in Tennessee. Credit: Noah Charney

The research indicates that the warming climate already is rapidly pushing many forests towards that tipping point, which may be reached as early as 2050: In addition to being rapidly exposed to temperatures they have not experienced in their lifetimes and are not evolutionarily prepared for, being hampered in their growth makes trees even more vulnerable to added stresses.

"There is a critical and potentially detrimental feedback loop going on here," Charney said. "When the growth rate of trees slows down in response to environmental stressors such as cold or drought, they can get by for a few years, but over time, they deplete their resources and are much more susceptible to additional stressors, such as damage by fire or a big drought or insect outbreaks. Year after year of slow growth therefore means forests become less and less resilient."

As a result, a forest can go from being a climate asset to a carbon producer very quickly.

"It's like a thermostat gone bad," Evans said. "Forests act as a carbon sink by taking carbon dioxide out of atmosphere, but the more the climate is warming, the slower the are growing, the less carbon they suck up, the faster the is changing."

"The results also highlight the potential importance of locally adapted forest management strategies to help mitigate the decreases in forest growth predicted by our analyses," Charney said.

The implications could potentially apply worldwide. While their models did not include data from outside the North American continent, it "seems very likely that the conclusions drawn in this study apply in the Eurasian forest as well," Evans said. "The boreal forests in Eurasia are more extensive and even more important than the ones in continental North America."

Explore further: Drought stalls tree growth and shuts down Amazon carbon sink, researchers find

More information: Noah D. Charney et al, Observed forest sensitivity to climate implies large changes in 21st century North American forest growth, Ecology Letters (2016). DOI: 10.1111/ele.12650

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15 comments

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BrettC
4.3 / 5 (7) Jul 20, 2016
It's all down to energy/nutrients. Higher elevations have less foliage so the trees would have less energy provided to them via nutrients. When it rains a great deal of the nutrients that are created there would be carried away by rain and end up in waterways. Building up the soil, to support the required changes, at higher elevations would take a lot longer than they probably accounted for in their study. That's why deforestation is so devastating. Cutting down all the trees and leaving them there would be bad enough, because each tree/plant recycles the energy provided to it each cycle. The Trees, however, are removed, which breaks the energy cycle and removes years worth of collected energy from the environment.
Bongstar420
3 / 5 (4) Jul 20, 2016
Since when do forests save the environment from climate change?
DiogenesDespairs
Jul 20, 2016
This comment has been removed by a moderator.
Steve 200mph Cruiz
4.3 / 5 (6) Jul 20, 2016
DiogenesDespairs,

Why should we go to a blog to learn about science? We can watch experiments and lectures on YouTube.
Anyone can post on a blog. There are a handful of people on this site I learn things from, but it's not like a two sided debate; I say what I think, someone says what they think, and more often than not actually, i'm usually wrong.
I almost always mess up my details and specifics, a combination of sloppy proof reading and just being wrong sometimes, but i'm wrong when i'm wrong.

But the climate change "debate" is a false narrative pushed by business interests and doesn't reflect reality.
We used to use lead in everything, often products we now make with oil byproducts, and even sealant for consumer canned foods. Eventually we found out lead was bad for you, the lead industry denied it and kept widespread use for decades, even though they knew better than anyone.
Same story for ciggarettes, in fact that they are the same lawyers denying climate change today
Maggnus
4.2 / 5 (5) Jul 20, 2016
Climate will do what climate will do as it has for hundreds of millions of years. Meanwhile, decisions and policy need to be based on hrd fact.

There are some crucial, verifiable facts - with citations - about human-generated carbon dioxide and its effect on global warming people need to know and understand at

hseneker.blogspot.com

The discussion is too long to post here but is a quick and eay read. I recommend following the links in the citations; some of the are very educational.

How disappointing. An utterly vacuous, empty, pile of drivel. There is nothing educational in that waste of computer memory.

Here, read this: http://www.skepti...nce.com/
antigoracle
2 / 5 (9) Jul 20, 2016
It would only amaze the ignorant Chicken Littles that these forests survived the 1930s when it was hotter and drier. Eat up Chicken Littles.
SamB
2.3 / 5 (3) Jul 20, 2016

How disappointing. An utterly vacuous, empty, pile of drivel. There is nothing educational in that waste of computer memory.


I thought the article was OK. Yes, nothing educational but it is entertaining to imagine the need to defend the forest from implied thwarting of Global Warming. I think we should give it a chance and see how it plays out.
kochevnik
1.6 / 5 (5) Jul 21, 2016
Since when do forests save the environment from climate change?
Until you chopped them down

Forests survived millions of years of climate change. But they may not survive zionist world order with their passion for inciting wars and fomenting hate
rrrander
1.8 / 5 (6) Jul 21, 2016
The frenzy to "forest" every inch of the West in the mindless belief we have to replace what was cut down. All it has done is reduce the amount of scrub land an sedge, and this has reduced wildlife and wildlife diversity. The ravenous in Asia are wiping out forested land very fast. That is where they should concentrate efforts to preserve forests.
antigoracle
1 / 5 (6) Jul 21, 2016
Thriving B.C. forests outpace pine-beetle CO2 losses by 2020

http://phys.org/n...tml#nRlv
marcush
1.6 / 5 (5) Jul 21, 2016

How disappointing. An utterly vacuous, empty, pile of drivel. There is nothing educational in that waste of computer memory.


I thought the article was OK. Yes, nothing educational but it is entertaining to imagine the need to defend the forest from implied thwarting of Global Warming. I think we should give it a chance and see how it plays out.


The quote referred to a comment, not the main article. Dah. Yes lets give global warming a chance! Lets see how it plays out! If civilisation goes belly up at least it will have been an entertaining ride!
barakn
4.3 / 5 (6) Jul 21, 2016
Thriving B.C. forests outpace pine-beetle CO2 losses by 2020

http://phys.org/n...tml#nRlv -antigoracle

Since the article was about "Projected change in forest growth rates for the second half of this century" you are talking about a different time scale and your comment is not germane to the discussion.
novaman
4 / 5 (4) Jul 23, 2016
Thriving B.C. forests outpace pine-beetle CO2 losses by 2020

http://phys.org/n...tml#nRlv -antigoracle

Since the article was about "Projected change in forest growth rates for the second half of this century" you are talking about a different time scale and your comment is not germane to the discussion.

right on barakn, as usual this coon sits glued to his screen 24/7 pressing buttons
HeloMenelo
3.7 / 5 (3) Jul 23, 2016
It would only amaze the ignorant Chicken Littles that these forests survived the 1930s when it was hotter and drier. Eat up Chicken Littles.


It wouldn't amaze us if you and your socks post another dumb comment
SURFIN85
5 / 5 (1) Jul 26, 2016
This is a news site, people.

No one is here to convince you of anything, yet here you are trying to convince everyone else of something. And taking a look at the responses, no one is buying the crap you're selling. So, what is your problem?

Prisonplanet.com is wide open for you to go party with your buddies. Have a bong. Relax.

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