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?
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.”
(Below is a press release from the researchers. A copy of the study is available here. – mk)
New research shows that western dry forests were not uniform, open forests, as commonly thought, before widespread logging and grazing, but included both dense and open forests, as well as large high-intensity fires previously considered rare in these forests. The study used detailed analysis of records from land surveys, conducted in the late-1800s, to reconstruct forest structure over very large dry-forest landscapes, often dominated by ponderosa pine forests. The area analyzed included about 4.1 million acres on the Mogollon Plateau and Black Mesa in northern Arizona, in the Blue Mountains in northeastern Oregon, and in the Colorado Front Range.
The reconstructions, which are based on about 13,000 first-hand descriptions of forests from early land surveyors along section-lines, supplemented by data for about 28,000 trees, do not support the common idea that dry forests historically consisted of uniform park-like stands of large, old trees. Previous studies that found this were hampered by the limitations inherent in tree-ring reconstructions from small, isolated field plots that may be unrepresentative of larger landscapes.
“The land surveys provide us with an unprecedented spatially extensive and detailed view of these dry-forest landscapes before widespread alteration” said Dr. William Baker, a co-author of the study and a professor in the Program in Ecology at the University of Wyoming. “And, what we see from this is that these forests were highly variable, with dense areas, open areas, recently burned areas, young forests, and areas of old-growth forests, often in a complex mosaic.”
The study also does not support the idea that frequent low-intensity fires historically prevented high-intensity fires in dry forests.
“Moderate- and high-severity fires were much more common in ponderosa pine and other dry forests than previously believed ” said Mark Williams, senior author of the study and recent PhD graduate of the University of Wyoming’s Program in Ecology.
“While higher-severity fires have been documented in at least parts of the Front Range of Colorado, they were not believed to play a major role in the historical dynamics of southwestern dry forests .”
Some large modern wildfires, such as Arizona’s Rodeo-Chediski fire of 2002 and the Wallow fire of 2011 that have been commonly perceived as unnatural or catastrophic fires actually were similar to fires that occurred historically in these dry forests.
The findings suggest that national programs that seek to uniformly reduce the density of these forests and lower the intensity of fires will not restore these forests, but instead alter them further, with negative consequences for wildlife. Special-concern species whose habitat includes dense forest patches, such as spotted owls, or whose habitat includes recently burned forests, such as black-backed woodpeckers, are likely to be adversely affected by current fuel-reduction programs.
The findings of the study suggest that if the goal is to perpetuate native fish and wildlife in western dry forests, it is appropriate to restore and manage for variability in forest density and fire intensity, including areas of dense forests and high-intensity fire.
• Only 23-40% of the study areas fit the common idea that dry forests were open, park-like and composed of large trees.
• Frequent low-intensity fires did not prevent high-intensity fires, as 38-97% of the study landscapes had evidence of intense fires that killed trees over large areas of dry forests.
• The rate of higher-severity fires in dry forests over the past few decades is lower than that which occurred historically, regardless of fire suppression impacts.
The study was published online last week in the international scientific journal, Global Ecology and Biogeography. The published article can be accessed online here. The title is: Spatially extensive reconstructions show variable-severity fire and heterogeneous structure in historical western United States dry forests.
The authors are Dr. Mark A. Williams and Dr. William L. Baker, who are scientists in the Program in Ecology and Department of Geography at the University of Wyoming. Dr. Mark A. Williams is a 2010 PhD graduate, and Dr. William L. Baker is a professor, both in the Program in Ecology and Department of Geography. In Dr. Williams’s PhD, he developed and applied new scientific methods for reconstructing historical structure and fire across large land areas in dry western forests. Dr. Baker teaches and researches fire ecology and landscape ecology at the University of Wyoming and is author of a 2009 book on “Fire Ecology in Rocky Mountain Landscapes.”
Dr. Mark A. Williams, Program in Ecology and Department of Geography, Dept. 3371, 1000 E. University Ave., University of Wyoming, Laramie, WY 82071. Email: email@example.com.
Dr. William L. Baker, Program in Ecology and Department of Geography, Dept. 3371, 1000 E. University Ave., University of Wyoming, Laramie, WY 82071. Phone: 307-766- 2925, Email: BAKERWL@UWYO.EDU.
For those of you who aren’t familiar with this paper, it was a recent effort to figure out if another approach to climate policy could be more successful.
Here is quote from Mike Hulme in this essay on the Hartwell paper .
To move forward, we believe a startling proposition must be understood and accepted. It is not possible to have a “climate policy” that has emissions reduction as the all-encompassing and driving goal.
We advocate inverting and fragmenting the conventional approach: accepting that taming climate change will only be achieved successfully as a benefit contingent upon other goals that are politically attractive and relentlessly pragmatic. Without a fundamental re-framing of the issue, new mandates will not be granted for any fresh courses of action, even good ones.
The paper’s first primary goal focuses on access; to ensure that the basic needs, especially the energy demands, of the world’s growing population are adequately met.
The second is a sustainability goal; to ensure that we develop in a manner that balances social, economic and ecological goals.
Third is a resilience goal; to ensure that our societies are adequately equipped to withstand the risks and dangers that come from all the vagaries of climate, whatever their cause.
Most regular readers of this blog will know that my approach to climate change for public lands is basically:
1. Do all the things we know we should have been doing (monitor and adapt in a transparent disciplined way)
2. Preferentially protect the fundamentals, especially water and air. There is no correct or incorrect composition of plants and animals, now or in the future.
3. Connect landscapes through riparian and other corridors.
4. Use land trades to decrease fragmentation of public lands and open areas to solar or wind development.
5. Develop sustainable biomass industries where needed to conduct fuels treatment or for ecological resilience.
I am also a big fan of Trout Unlimited’s “protect, reconnect and restore” as described in their “Healing Troubled Waters” document here.
So here’s the question- think about Hulme’s concepts, my concepts, TU’s concepts and your own concepts of what to do about climate change… what is the public lands piece to you? And what, if any of that should fit into a planning rule?