Dead Forests Release Less Carbon Into Atmosphere Than Expected

According to new research, lead by researchers at the University of Arizona, trees killed in the wake of mountain pine beetle infestations in Colorado have released less carbon into the atmosphere than expected.  Read about the research and hear from the scientists in this article from the University of Arizona, excerpts of which are also highlighted  below.  And High Country News wins the award for best headline of the day, “Good news for people who love bad news,” which contains even more information about the new research.  What does this new scientific research say about the validity of the oft-repeated claims from the timber industry and others that we have to cut down our forests so that we can”lock up” that carbon in 2 x 4’s?
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Massive tree die-offs release less carbon into the atmosphere than previously thought, new research led by the University of Arizona suggests.  Across the world, trees are dying in increasing numbers, most likely in the wake of a climate changing toward drier and warmer conditions, scientists suspect. In western North America, outbreaks of mountain pine beetles (Dendroctonus ponderosae) have killed billions of trees from Mexico to Alaska over the last decade.

Given that large forested areas play crucial roles in taking carbon dioxide out of the atmosphere through photosynthesis and turning it into biomass, an important question is what happens to that stored carbon when large numbers of trees die.

“The general expectation we had was that when trees die on a large scale, it would lead to a big pulse of carbon into the atmosphere through microorganisms metabolizing all that dead wood,” said David Moore, an assistant professor in the School of Natural Resources and the Environment in the UA College of Agriculture and Life Sciences and one of the lead authors of the study, which is published online in the journal Ecology Letters.

“A question we are looking to answer is, ‘How does the carbon dioxide released from the forest into the atmosphere change as you have large scale tree mortality over time?”’ said second lead author Nicole Trahan, a postdoctoral researcher at the University of Colorado, Boulder.

According to co-author Russell Monson, who is the Louise Foucar Marshall Professor in the UA School of Natural Resources and the Environment, forests affect the carbon budget of the atmosphere through two dominant processes: photosynthesis, by which plants take carbon dioxide out of the atmosphere and lock it up in organic compounds, and respiration, by which plants and soil microbes release carbon dioxide back into the atmosphere. The balance of these processes determines whether a particular forest is a carbon source or a carbon sink.

After a massive tree die-off, conventional wisdom has it that a forest would go from carbon sink to carbon source: Since the soil microbes are still around, they are expected to release large amounts of the greenhouse gas carbon dioxide into the atmosphere, where it is thought to accelerate climate change.

Surprisingly, we couldn’t find a big pulse,” said Moore, who is also a member of the UA Institute of the Environment.

Trahan added: “In the first few years after beetles have come in and killed trees, the carbon release from the surrounding soil actually goes down.”

Large amounts of dead trees, it turns out, hold on to their carbon for a long time and prevent it from quickly being released into the soil or the atmosphere. According to Moore, this might be due to several reasons: First, while trees take up carbon dioxide during the day during photosynthesis, they release some of it at night when they switch to respiration.

“Once the trees are dead, respiration by the trees goes away,” Moore said. “In addition, if you cut off the carbon that a tree put into the soil while it was alive, you reduce the ability of the soil microbes around the roots to respire.”

“After five or six years, there is a buildup of some dead plant material, leaf litter and so on, and that seems to drive the rate of respiration up again. But it never recovers to the point it was before the beetles killed the trees, at least over the span of a decade,” Moore said.

Finally, the trees studied in this project grow at higher elevations, where cooler temperatures slow the decomposition process and thereby carbon-releasing respiration.

“Overall, we discovered that after a tree die-off, the loss of carbon in the soil results less from increased respiration by microbes but more from the fact that trees are no longer sequestering photosynthesized carbon into the soil,” Moore said. “There seems to be a dampening of the carbon cycle rather than a big pulse of carbon release. So even if the forest now goes from a sink to a source of carbon dioxide, it’s not as dramatic of an effect as we thought it would be.”

25 Comments

  1. Matt:

    What happens to the “carbon pulse” when the dead trees burn, such as in the Tillamook Fires, the B&B Complex, or the Biscuit-Silver Complex?

    Question 2: were these researchers working under some kind of taxpayer-funded Global Warming proposal? It would be interesting to consider their findings in light of their original funding proposal — and in light of who paid the bills on this.

    • Bob, if you look over the study you’ll see that the source of funding was clearly provided at the end of the article.

      This study was funded by the Climate and Environmental Sciences Division of the Office of Biological and Environmental Research at the US Department of Energy through grant award: ER65077 and the UK Natural Environment Research Council through award: NE/H000909/1 and also the support the University of Colorado Mountain Research Station and the USFS Fraser Experimental Forest. The authors thank Emily Dynes, Clare Gibson, Meredith Casciato, Mitch Kremm, Jennifer Morse and Banning Star for field assistance, Michael Weintraub and Laura Scott-Denton for logistical and technical support and David Schimel for comments on early drafts of the manuscript.

      • Thanks, Matt: Looks like my “hunch” was correct. More government “climate change” science. Those are rhetorical questions regarding what appear to be basic flaws in the study. Why would I want to ask someone about wildfire-related carbon pulses when it is my own field of study, and I already have a good network of knowledgeable researchers and resource managers to consult with? I had never heard of David Moore before. Here’s why: http://www.environment.arizona.edu/david-moore

  2. Bob,

    I’m pretty sure the funding sources had nothing to do with the outcomes of this study what-so-ever.

    More importantly, we need to take note of where this study was. Soil processes associated with cold, high elevation forest sites can not be blown out of proportion and say that this applies to ALL forest sites with MPB mortality.

    No two soils are the same. No two forest act in the same manner. All have different parent materials, temperature and precipation regiemes, and disturbance histories. The results printed here are from one location and have limited utility for forecasting soil processes over large spatial areas though this is sadly what appears to be happening.

  3. Bob- I was going to wait until I saw the study, but since you started…it seems kind of silly. We can drive around and see the trees standing. That’s where most of the carbon is.

    Who would expect a “pulse” when we an observe how long it takes a tree to break down in various places based on a primitive sensing apparatus – our eyeballs?

    And it takes longer when it’s cold and dry. I think I learned that in the early 70’s in school, but anyone who walks around in the woods knows it.

    I wonder if they could be more specific about whose idea it was that we would see a pulse of carbon coming off forests, when we can drive through those forests and see the carbon right there.

    • I think a real problem with much of the “research” going on today is that the modelers who do this stuff rarely ever get into the actual forests to ground-truth their “findings.” Somehow, their belief in simplistic simulated realities seems to trump actual conditions — with which a growing number of them seem totally unfamiliar.

      Another problem is Smokey’s declaration: “I’m pretty sure the funding sources had nothing to do with the outcomes of this study what-so-ever.” Either he’s an “insider” who uses his anonymity to hide from coworkers, or he’s just blowing smoke — and has a lot of trust in these guys and their employers. This certainly has all the appearance of a “cause-and-effect” process in the funding aspects of the study. Why else do it? And for whom?

      It’s a stupid study that must have had someone pay for it for some reason. I’m guessing ignorant taxpayers in the pay department, and registered Democrats in the design department. And yes, I think “climate change” is more of a polarized political process than a “pure science” enterprise.

      • How can we un-polarize climate change science discussions when a study such as this is called “stupid” and designed by “registered Democrats” in a sneering tone? Why would various viewpoints engage in discussion here if this is where the conversation inevitably leads?

        • John: I am neither a Republican or a Democrat — probably the polar opposites of both. It’s difficult to differentiate between wry, ironic humor and sneering in text, and I refuse to use emoticons.

          My actual sneering tone was probably more aligned with the word stupid, which was in reference to the “findings” of this study, and the “inferences” (and even “bald statements”) supposedly derived from them. The word is used out of exasperation and as typically defined — why I didn’t use “ignorant” or “poorly defined,” as examples, instead. More exacting reasons for this word choice are given in the comments of others. The study, at best, simply confirms what everybody already knows that is familiar with forests or forestry, and is distinctly limited to a very small testing area over a very short period of time. No need to generalize the results — and particularly to such a grandiose scale. Why did DOE (“taxpayers”) fund this study in the first place? And whose “expectations,” exactly, weren’t being met. And how much is “huge?” It’s a stupid study. In my opinion.

          I have been involved in the climate change discussion since its beginnings, and even delivered a peer-reviewed paper for EPA at an international conference regarding climate change predictive models then in use (the “James Hanson era”), and the related potential for sequestering carbon in conifer plantations. To help mitigate Global Warming. That was about 20 years ago, and my EPA research funding ended immediately and the report wasn’t published by EPA and directly delivered to closets until a few years later. Since then, I (and many others) have noted the political division between the “believers” (typically, Gore Democrats) and the “deniers” (typically, Tea Party Republicans). Check out some Congressional voting patterns on the topic to see what I mean.

          And, personally, I have no real interest in un-polarizing the topic. I just happen to believe it is more a political issue (where polar views are useful and expected) than a science issue (where skepticism is very important).

          • Yep. And regular newspaper blogs, letters to the editors, and even courts of law. Personally, I think this blog does a pretty good job of self-policing in those regards, and everyone seems more than willing to call one another out when any of us start getting too far out of line. (I’d put in a sincere smiley face here if I knew how to do emoticons.)

        • Smokey: Here is an excellent example of why I do not like to get into discussions with anonymous people. I have no idea who you are. You claim to know other people I don’t know. Further, you claim that I “insulted them,” but don’t say what it is I wrote that insulted whoever it is I don’t know. Wow. Sorry for not owning this, but I think I hear your Mom calling.

          Smokey, when I first read your previous answer I actually laughed out loud — because I thought you were joking by stating “I’m pretty sure the funding sources had nothing to do with the outcomes of this study what-so-ever.” Yeah — right! Then I figured — maybe not. Maybe you actually believe that . . . so I tried to respond accordingly.

          Were your nameless associates insulted by my speculating whether they were soaking up Global Warming dollars or not with their study — before finding out they were, indeed, being funded by the “Climate and Environmental Sciences Division of the Office of Biological and Environmental Research at the US Department of Energy” (which seems an odd choice to fund a forest research project — unless it has something to do with Global Warming.) Or were they insulted because I speculated that some of the field work may have been done by “grad students?” Why or why not?

          Sorry, Smokey, if a real person is insulted by something I really said, then that is too bad. It wasn’t intentional, and certainly not (and couldn’t have been) directed at them, personally. I’d have to at least know what it was I said and who — exactly — was insulted, and why — exactly — they felt insulted before I could have even the slightest idea how to go about making amends. Assuming they were warranted. The only thing I have to go on at this point is the second-hand word of a nameless individual I’ve probably never met. Can’t help you, bud. Or your acquaintances, whoever they are, too.

          • Damn dude…you are one jaded individual and I’m sorry for you. All I’m saying it that alot of hard work and effort goes into these studies from numerous much smarter than yourself. And for some ass clown to cowardly suggest that they and their science is minipulated by money is insulting. Period.

            Why don’t you actually read the paper and come back with some solid evidence against the science rather than the easy out of taking a low blow at their intergity.

            As for me…yeah, i keep a low internet profile. No facebook, blogs, or my name all shit splattered across the web. Maybe you should take note.

            • I have taken note. You are a nameless individual that hides behind a pseudonym and, by his own admission, is frightened by modern communications and the possibility of being responsible for his own thoughts and accusations. I have no idea who you are, and could care less about your opinions as a result. I also have absolutely zero interest in following your lead, but thanks for the suggestion. I think I understand your need for keeping a “low internet profile,” though.

              And, if someone wants to pay me for reading through this document and commenting on it (why Gore invented Titles and Abstracts in the first place), I’d be more than happy to do so. I’m guessing people I don’t know might be insulted, though. Where’s all that smoke coming from, Smokey? Let me guess.

  4. Bob Zybach :

    I think a real problem with much of the “research” going on today is that the modelers who do this stuff rarely ever get into the actual forests to ground-truth their “findings.” Somehow, their belief in simplistic simulated realities seems to trump actual conditions — with which a growing number of them seem totally unfamiliar.

    So Bob, are you saying that your opinion about much of the “research” today applies to this study we are discussing here?

    Also, the study clearly states:

    “The authors thank Emily Dynes, Clare Gibson, Meredith Casciato, Mitch Kremm, Jennifer Morse and Banning Star for field assistance.”

    So it seems to me as if the authors and at least a half dozen assistants were out in the field. You may want to either contact the lead author of the study directly or review the “Materials and Methods” portion of the study to learn more about where and how it was conducted.

    • Uh-oh. Looks like another “Matt n’ Bob Show,” if we’re not careful. Yes, I’d guess this is the type of modeling that would fit my description. Plus, it depends what the people were doing in the field, how that fit the proposed methodology, and what their documented findings were. I’m guessing grad students getting some “field experience” credits? I’m wrong on these things lots of times, but it is bothersome with how many times I appear to be right.

      • can we step back a minute? thanks, Matthew for posting the link. I think it’s really important how we got from Fraser experimental forest and a (field) and modeling study to “Mexico to Alaska”.

        1. What the heck is DOE doing funding studies that the FS or USGS could have funded that deal with carbon fluxes in forests? We might not need draconian sequestration responses if we simply looked at what research projects are designed to find out and assign funding to one agency to coordinate. It’s actually kind of embarrassing that it is so fundamentally disorganized.

        2. There are a couple of interesting paragraphs I found..

        Globally we have seen a large increase in the rate and extent of forest mortality in recent years (Allen et al. 2010). After insect induced mortality, standing dead trees may remain for several decades (Harmon et al. 1986; Edburg et al. 2012; Hicke et al. 2012). Given the cold temperatures prevalent in mountain forests and the long-term effects of substrate limitation on decomposition, carbon may remain stored in forest ecosystems for long periods after this current, widespread insect outbreak in the absence of rapid release by fire. A study spanning 100 years of fire and beetle disturbance records found no increased occurrence of fire at locations previously infested by beetles (Kulakowski & Jarvis 2011), so release of carbon by decomposition is likely. We have coupled direct experimental manipulations with long-term monitoring to elucidate the mechanisms controlling the release of CO2 by decomposition after insect disturbance. In this study, reduced GPP strongly limits respiration after tree mortality and, for up to a decade after the disturbance the current paradigm of simple first order control of ecosystem respiration cannot explain the observed patterns. In addition to studies of how disturbance influences the soil microclimate, it is likely that a more complete treatment of non-equilibrium microbial respiration may be required to confidently model how widespread tree mortality will change long-term carbon balance.

        Let’s just follow the logic here… carbon can remain stored because it takes a long time to break down when it’s cold and dry. TRUE

        There won’t be any more fires in the future than in the past, (but I thought climate studies showed there would be “megafires” and more than in the past, bark beetle or not?). This is one of these “the science tells us climate change will bring unprecedented conditions” but “we will base our scientific models of the future on past history” kinds of paradoxes.
        We also suppressed fires to varying degrees in the last 100 years, and probably more so today, because more people are out there and our technology is better, so how could the past 100 years possibly be predictive?

        We need to do more studies so we can model (confidently!) what happens to the soil when widespread tree mortality occurs because we can see the tree carbon for ourselves.

        However, we probably can’t do anything about soil carbon that would make much of a difference, and the trees are going to stay dead, either burned in piles or in someone’s den or heating someone’s house. I think the abstract, as usual, is more helpful than the press release…

        Amid a worldwide increase in tree mortality, mountain pine beetles (Dendroctonus ponderosae Hopkins) have led to the death of billions of trees from Mexico to Alaska since 2000. This is predicted to have important carbon, water and energy balance feedbacks on the Earth system. Counter to current projections, we show that on a decadal scale, tree mortality causes no increase in ecosystem respiration from scales of several square metres up to an 84 km2 valley. Rather, we found comparable declines in both gross primary productivity and respiration suggesting little change in net flux, with a transitory recovery of respiration 6–7 years after mortality associated with increased incorporation of leaf litter C into soil organic matter, followed by further decline in years 8–10. The mechanism of the impact of tree mortality caused by these biotic disturbances is consistent with reduced input rather than increased output of carbon.

  5. Update – I wrote Dr. David Moore and he responded:

    I should point out that our study found that there had not been a huge spike in CO2 from 2 forest systems in Colorado where we carried out our field research. The findings should not be applied to warmer, moister forests, where dead trees may decay faster.

  6. I am not sure why Bob Z is so quick to assume that a “carbon pulse” from reburn will erase or diminish the value of carbon that is stored in dead trees. Virtually all forests will reburn at some point. Some will reburn long after the trees die, and a few will reburn shortly after the trees die, but neither of those extremes are representative.

    The point is that the dead trees store carbon day after day, year after year, until that carbon either combusts or is respired by a heterotroph. Carbon storage builds while a plant is alive and photosynthesizing. Carbon storage probably peaks around the time of death, and trees continue to store carbon long after they are dead.

    Anecdotes about rapid reburn are not very useful because they don’t accurately represent the whole population of dead trees. What really matters is the landscape average time it takes for carbon in dead trees to migrate to the atmosphere.

    I suspect that people with unorthodox views on climate change may also find it difficult to think clearly about forests and carbon.

    • Tree: Is it possible that you are the one — and not others “with unorthodox views” (in your opinion) — that is finding it “difficult to think clearly about forests and carbon?” That’s another possibility, and it is also a reasonable rhetorical question to consider.

      When you say: “What really matters is the landscape average time it takes for carbon in dead trees to migrate to the atmosphere,” I have to figure that you and I have major differences in our personal perceptions of “what really matters.”

      People who think that it is a really important “ecosystem service” for forests to store carbon (I’m not a member of that particular belief system), seem to almost always disregard the part of the tree that remains underground after a clearcut or salvage logging operation. It’s a lot of carbon! My personal preference is to manage our forests for the old standby purposes of marketable products, clean water, healthy wildlife populations, human safety, fresh air, and abundant recreational (including spiritual) opportunities. Then think about carbon sequestration and atmospheric migration rates.

  7. When you can see plumes of smokey pollution from space, coming from wildfires, that cannot be “natural and beneficial”. When wildfires leave more dead fuels than when they started, re-burn is inevitable. And, what do you think happens to all those toxic gases and carbon from wildfires? When those plumes go into our upper atmosphere, plants cannot re-sequester that “pollution”. Additionally, climate models seem to ignore that fact that severely-damaged soils cannot support the same levels of carbon-sequestering vegetation that it did before the fire. Even the soils, themselves, lose soil carbon for several feet down.

    Finally, many studies exclude human ignitions, and their impacts. We simply aren’t going back to “pristine” conditions, anytime soon.

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