The Case of the Dying Aspens: “A Widespread Climate-Induced Forest Die-Off” from a “Global Change-Type Drought”

Over the past 10 years, the death of forest trees due to drought and increased temperatures has been documented on all continents except Antarctica. This can in turn drive global warming by reducing the amount of carbon dioxide removed from the atmosphere by trees and by releasing carbon locked up in their wood.

That’s from the news release for a new Proceedings of the National Academy of Sciences study, “Roles of hydraulic and carbon stress in a widespread climate-induced forest die-off.”

A common myth is that higher levels of CO2 will be good for all vegetation.  Unfortunately, those higher levels of CO2 are accompanied by higher temperatures and, in many places, drought and bark beetle infestation, which are bad news for trees — as study after study has documented (see links below).

The new study spells this out for the trembling aspen (Populus tremuloides), which goes by many other names, including the white poplar, though, as it turns out, the aspens apparently now have reason to tremble — manmade global warming.  Fittingly, the aspen die-off is “called Sudden Aspen Decline or SAD.”

The study has a nice overview and notes with the key recent studies:

Forests are important carbon sinks, yet they are threatened by global change (1, 2). In the past decade, widespread forest mortality related to drought or temperature stress has been documented in multiple biomes and on all vegetated continents (3–6). In temperate North America, some of these events have been linked to “global change-type droughts,” defined as severe drought coupled with elevated summer temperatures (6–9). Such mortality events can radically transform regional land cover and effect biodiversity, fire risk, ecosystem function, land–atmosphere interactions, and ecosystem services (10–12). Furthermore, forest diebacks can lead to dramatic decreases in net primary production and carbon sequestration, driving these ecosystems to become CO2 sources and to have a positive feedback to climate warming (11, 13–17). Climate-mediated die-off of pine forests caused by insect outbreak in Canada led to estimated carbon emissions of 990 Mt CO2e (CO2 equivalent) over a 20-y period, equivalent to 5 y of Canada’s annual transportation sector emissions (200 Mt CO2e/y) (15)

There is every reason to think things will get much worse if we stay on our current emissions path (see Science: Second ’100-year’ Amazon drought in 5 years caused huge CO2 emissions. If this pattern continues, the forest would become a warming source).

This PNAS study explores the cause of the climate-induced forest die-off, and explains how droughts kill trees:

New research led by Carnegie researcher and Stanford University PhD student William Anderegg offers evidence for the physiological mechanism governing tree death in a drought….

Forests store about 45 percent of the carbon found on land. Their mortality can radically transform ecosystems, affect biodiversity, harm local economies, and pose fire risks, as well as increase to global warming.

Scientists had two competing theories for how forest trees die during a drought. One hypothesis proposed that the trees starved due to decreased photosynthetic activity. The other proposed that the system for transporting water within a tree was damaged beyond repair due to the stresses of the drought.

Without knowing which theory was correct, it was difficult for researchers to build models and make projections about the larger impact of drought-induced forest mortality.

The team focused their efforts on climate-induced die offs of trembling aspen trees in North America. They looked directly at both carbon starvation and water-transportation stress on ongoing forest deaths….

The aspen die-off, called Sudden Aspen Decline or SAD, began after severe droughts between 2000 and 2004 and affects about 17 percent of aspen forests in Colorado, as well as parts of the western United States and Canada. SAD continued through 2010, when the research was conducted.

“Large scale mortality events, such as we see with aspens, are the dynamite in ecosystem responses to climate change.  We know that when they occur, they make a huge difference. But we are at the early stages of being able to predict occurrence,” said Field, director of Carnegie’s Department of Global Ecology and professor of biology and of environmental Earth systems science at Stanford.

The team found no evidence of significantly decreased carbon reserves in SAD-affected aspens. This undercuts the starvation theory, although it is possible that carbon starvation had occurred and already been rectified.

By contrast they did find notable losses of function in the tree’s water-transportation systems, especially in the roots. SAD-affected trees showed about a 70 percent loss of water conductivity. Potted trees exposed to a summer’s-worth of drought exhibited significant root mortality.

“Our study provides a snapshot of what future droughts could hold for the emblematic tree of the American West. Our results indicate an impaired ability to transport water due to drought damage plays an important role in the recent die-off of aspens,” William Anderegg said.

What’s particularly worrisome about this drought-induced tree mortality is that droughts — and especially the hot weather “global change-type droughts” — are projected to get considerably more frequent and intense (see “Must-read NCAR analysis warns we risk multiple, devastating global droughts even on moderate emissions path“).

Now that’s SAD.

Related Posts:

“These results are extraordinarily significant because they show that the global net effect of climatic warming on the productivity of terrestrial vegetation need not be positive “” as was documented for the 1980′s and 1990′s,” said Diane Wickland, of NASA Headquarters and manager of NASA’s Terrestrial Ecology research program”….

“This is a pretty serious warning that warmer temperatures are not going to endlessly improve plant growth,” Running said”….

“The potential that future warming would cause additional declines does not bode well for the ability of the biosphere to support multiple societal demands for agricultural production, fiber needs, and increasingly, biofuel production,” Zhao said.

25 Responses to The Case of the Dying Aspens: “A Widespread Climate-Induced Forest Die-Off” from a “Global Change-Type Drought”

  1. Solar Jim says:

    Thank you Joe. Please also post on the Russian observations (AGU, Independent) of multiple methane exhaust plumes coming from Siberian continental shelf clathrates.

    After decades of hot-air talk about a “global response” it would seem all the natural physical responses are ominously accelerating toward destabilization. Perhaps we at least had a chance for “sustainable economic restructuring” in the last century.

  2. B Waterhouse says:

    The newspaper stories cite release of this study at the AGU convention. However, I attended AGU last week and did not see this study in the program nor can I find it online, with the sole exception of repetition of the original press report on various websites and blogs.

  3. John McCormick says:

    I agree. Some confusion about the paper being presented at AGU. Perhaps not enough time since the research team concluded their survey. We can expect to hear a great deal more about this…show stopper.

  4. Leif says:

    Joe, I would like to make a suggestion for a possible post. With the continual carpet bombing of impending doom that we on the front lines are exposed to daily, I see a type of Post Traumatic Stress Syndrome. Perhaps a new name is in order. Climatic Disruption Stress Syndrome? CDSS. Sensory Overload Carbon Stress? SOCS. Not only do I see distress in myself but others as well. It may in fact be a defense mechanism that people use to willfully remain ignorant of the problem and thus the solutions and the necessary action.

    I am sure that area is ripe for harvest and that you will have access for some insights, if not personally certainly within reach.

  5. Raul M. says:

    According to some who do impose personal poregogive, it is not always the thing to give the information of the oncoming hardship. Especially in cases of a young child having cancer. Right or wrong some do exclude other opinions.
    The reasons of exclusion are myriad, so one may find oneself excluded for expressing the right to know opinion. Such is life and the excluders may find they do need ones help.

  6. Leif says:

    I do not believe the “ignorance is bliss” metaphor can be an option in this case.

  7. Mike Roddy says:

    Forest mortality in the US as a while is up
    59% from 1986 to 2006, the latest figures that have been collected, according to USDA. This is before the recent huge beetle kills in the Rockies.

    That’s an unheard of increase, since spikes on that scale are very rare in forest inventory studies.

    The public has not been told, except in the journals. I wonder why? Does USDA not want to let people know that maybe we can’t keep up our rate of logging and development due to degradation from climate change and coal plant pollution?

  8. Josh Balik says:

    Paleontologist Michael Benton argues in his book about mass extinctions, ‘When Life Nearly Died,’ that species have more or less equal odds of surviving an extinction event. Still I can’t help but feel that the Aspen, being a transition species marking the boundary between biomes, is particularly vulnerable to climate change, the likes of which are tied to all mass extinctions. Furthermore many aspen groves are technically single organisms sharing an expansive root structure. The aspens that lived in the forest where I grew up have gone the way of the dogwoods. They were such shimmering elegant trees.

  9. prokaryotes says:

    In a not so far future, people will just wonder WHY and How we could let this happen, when we have all the knowledge, skills and motivation to do so in the first place!

    Get off your ass! Move it! Now!

    On the bottom line, this is good for economy (even if you do not see results simultanously)

  10. Leif says:

    Tree mortality has increased to 5% per year in Canadian Forests do to water stress from changing weather patterns.

  11. Joan Savage says:

    I’m pitching for more information on changes in forest soils in climate change.

    Aspens are important species in ecological succession and soil formation. Soil mycorrhizae that are symbiotic with aspens are part of the natural carbon sequestration process that is at risk.

    Part of the stress on aspens could be shifts in soil biota around their roots, as the soil temperature regime shifts.

  12. Colorado Bob says:

    More Shrubbery in a Warming World

    ScienceDaily (Dec. 8, 2011) — Scientists have used satellite data from NASA-built Landsat missions to confirm that more than 20 years of warming temperatures in northern Quebec, Canada, have resulted in an increase in the amount and extent of shrubs and grasses.

  13. Colorado Bob says:

    December 14, 2011
    Climate Change Blamed for Dying African Trees

    A lot of trees are dying in Africa’s Sahel region and new study says climate change caused by humans is to blame. What’s more, many tree species are also disappearing.

    The study appears in the Journal of Arid Environments. Climate change scientist Patrick Gonzalez led the research on six countries. At the time of the study, Gonzalez was a visiting scholar at the Center for Forestry at the University of California at Berkeley.

  14. Colorado Bob says:

    ScienceDaily (Dec. 14, 2011) — In a hundred years trees may be growing where there are now glaciers. The warm climate of the last few years has caused dramatic melting of glaciers in the Swedish mountains. Remains of trees that have been hidden for thousands of years have been uncovered. They indicate that 13,000 years ago there were trees where there are now glaciers. The climate may have been as much as 3.5 degrees warmer than now. In other words, this can happen again, according to Lisa Öberg, a doctoral candidate at Mid Sweden University in a new study.

  15. bones288 says:

    If these shrubs are growing where peat bog use to be . . . that’s actually not a good thing. A shrub and some surrounding grass will not suck up enough GHG to compensate for the several feet of decaying organic matter under neath the roots. I could be wrong.

  16. B Waterhouse says:

    Turns out it was presented as a poster at AGU, not a lecture:

    SESSION TITLE: GC41B. Permafrost and Methane: Monitoring and Modeling Fluxes of Water and Methane Associated With Arctic Changing Permafrost and Coastal Regiona I Posters

    AUTHORS (FIRST NAME, LAST NAME): Natalia E Shakhova1, 2, Igor Peter Semiletov1, 2, Anatoly Salyuk2, Chris Stubbs3, Denis Kosmach2, Orjan Gustafsson4

    INSTITUTIONS (ALL): 1. IARC, Univerrsity Alaska Fairbanks, Fairbanks, AK, United States.
    2. Laboratory of Arctic Research, Pacific Oceanological Institute FEBRAS, Vladivostok, Russian Federation.
    3. University of California, Marine Science Institute, Santa Barbara, CA, United States.
    4. Institute of Applied Environmental Research, Stockholm University, Stockholm, Sweden.

    Title of Team:

    ABSTRACT BODY: The high-latitude, shallow ESAS has been alternately subaerial and inundated with seawater during glacial and interglacial periods respectively. Subaerial conditions foster the formation of permafrost and associated hydrate deposits whereas inundation with relatively warm seawater destabilizes the permafrost and hydrates. Our measurements of CH4 in 1994-2000 and 2003-2010 over ESAS demonstrate the system to be in a destabilization period. First estimates of ESAS methane emissions indicated the current atmospheric budget, which arises from gradual diffusion and ebullition, was on par with estimates of methane emissions from the entire World Ocean (≈8 Tg-CH4). Large transient emissions remained to be assessed; yet initial data suggested that component could increase significantly annual emissions. New data obtained in 2008-2010 show that contribution of ebullition-driven CH4 fluxes from shallow hot spots alone could multiply previously reported annual emission from the entire ESAS.

  17. B Waterhouse says:

    There was also a press conference at AGU as reported here:

    I hope they publish a peer-reviewed article soon. The importance of their preliminary findings, if confirmed, cannot be overstated.

  18. Raul M. says:

    Would still be a not seen before event- guessing almost all boaters have nada experience in how to navigate those waters — exclusion for just that reason.
    As an excluder for that reason I would say a boat that has only bubbles won’t float. And I would say that the air might be in the realm of methane concentration that makes sewage gasses on of the top 10 ways Americans poison themselves. Check Tabers Medical Dictionary appendixes for most common.

  19. Joan Savage says:

    The poster abstract was submitted in advance, so let’s note the abstract did not include 2011 data. The 8 Tg-CH4 emission estimate is pre-2011; we should expect a revision upward from that, based on the news article.

  20. Mossy says:

    Leif, I call it Climate Awareness Depression, or CAD for short.

  21. Joan Savage says:

    Check the date stamp. This has been an ongoing issue!

  22. Mulga Mumblebrain says:

    Leif, I reckon it is ‘Pre-Traumatic Stresses Syndrome’, because they will be multiple, they are synergistic, and we are not used to coping with disasters of the coming magnitude. Some will grow stronger (not that it will do ’em much good) and many will go troppo, with, shall we say ‘unfortunate’, results.

  23. Mulga Mumblebrain says:

    Mike, as far as the capitalists who run the planet are concerned, forests are just big piles of stuff not yet turned into money. They will cut every stick down, and that includes national parks which they envisage being ‘privatised’. In the perverted reptilian brains of these creatures, allowing the forests to become degraded offers the opportunity to declare that this is yet another example of ‘public inefficiency’, best cured by a rapid transfer to the private sector. For these creatures ‘stimulating the private sector’ is more than a hobby, it is a religion.

  24. perceptiventity says:

    Kathy McMahon of Peak Oil Blues has been helping many deal with the psychological issues one faces when grasping the reality and severity of peak oil.

  25. John McCormick says:

    Joan, you have a sharp eye. Thanks for clarification.