Study: Mature forests may be limited in their ability to absorb “extra” carbon dioxide

We’ve discussed this issue in several threads, such as here. A new study by a large group of researchers, recently published in Nature, looks at the ability of mature trees to absorb CO2. The conclusion is that “additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus.”

An open-access companion article, “Mature forest shows little increase in carbon uptake in a CO2-enriched atmosphere,” adds perspective and discusses the need to additional research.

12 thoughts on “Study: Mature forests may be limited in their ability to absorb “extra” carbon dioxide”

  1. Some of us were taught this in the mid ’60s.
    We even had total volume graphs showing the inflecton points @ accelerated growth and @ the start of senescence and then @ the peak followed by a steady decrease in volume/carbon.

    • This study did NOT say that mature forests stop grow, it said there is no bonus growth from the CO2 enriched atmosphere. I doubt that was covered in your mid-60s forestry classes.

      Research in a 500-year-old stand at Wind River (and other sites) clearly show that old forests continue to grow and store more carbon over time.

      • This study also does not say that forests should be allowed to lose its sequestered carbon through inaction. Dead forests in the Sierra Nevada will be losing huge amounts of carbon, through inevitable firestorms. Should we ignore forest health while preserving dead forests?

  2. Gil, has a point… old trees don’t grow as fast, and sometimes don’t respond as well to things like thinning, fertilization, CO2 enrichment.

    I think the companion article did a really good job of explaining the study and the context. Hurray for them!!!

    But, given that, I don’t understand why folks think that this is important to study on a worldwide basis, because forests are different by species, age, mix of species, site and so on. And then they unpredictably die off on you via fire or insects (or disease, as per American Chestnut). So again, the effort to, and our ability to keep up with CO2 enrichment seem out of proportion to the utility of knowing about it. IMHO. As the authors say,

    The bottom line is that it is currently difficult to estimate the size of the global CO2-fertilization effect accurately. To solve this problem, we need to know more about hierarchical constraints not only across spatial scales, from ecosystem sites to regions and the globe, but also across biological scales — from the molecular level of biochemical reactions, to the leaf and canopy scale, and through to the larger scales associated with plant production and ecosystem carbon pools.

    I guess we need to understand everything globally at all spatial and temporal scales. Sounds impossible and expensive.

  3. Even if forests switch from sink to source (btw, not what this study found), it is still critically important to conserve old forests because logging will just accelerate the transfer of carbon from the forest to the atmosphere. It’s better to have the spigot leaking a trickle than a firehose.

  4. Congress is thinking about this question, too, with the “Growing Climate Solutions Act.”

    “The bill would direct the U.S. Department of Agriculture (USDA) to develop a suite of programs to support greenhouse gas (GHG) reductions and carbon sequestration through agriculture and forestry, by providing technical expertise and clearer access to markets.,-Brook%20Detterman%2C%20Zachary&text=Late%20last%20week%2C%20a%20bipartisan,the%20agriculture%20and%20forestry%20sectors.

    “This to me is timely. It makes sense. It covers a fairly large section of where we have CO2 making it into the atmosphere,” Sen. Mike Braun (R-Ind.), a tree farmer and a lead sponsor on the legislation, said in an interview.

    I was intrigued by this interpretation in the Washington Post: “Forest managers, similarly, can sequester carbon by letting more trees grow to maturity rather than regularly cutting them down.”

    But I haven’t found a copy of the bill. It sounds like Congress would give USDA (i.e. the Forest Service) the job of sorting out the question of what kind of forestry should be certified as carbon-beneficial.

    • When I read this part “This legislation is specifically targeted at three “roadblocks” holding back domestic farmers, ranchers, and private forest owners from participating in GHG markets: (1) uncertainty about how to implement projects or navigate carbon markets; (2) uncertainty regarding trustworthy players in carbon markets; and (3) a lack of agricultural or forestry expertise by existing carbonmarket participants.” It sounds like helping those folks figure out how to access carbon markets (not determining if they fit the markets, that’s up to the market.)

      Existing carbon markets also may lack ag or forestry expertise and USDA could help. That still doesn’t give USDA authority over determining what carbon markets want.

      As to its own programs, USDA announced these goals in February:

      Carbon Sequestration and Greenhouse Gas: Enhance carbon sequestration through soil health and forestry, leverage the agricultural sector’s renewable energy benefits for the economy, and capitalize on innovative technologies and practices to achieve net reduction of the agricultural sector’s current carbon footprint by 2050 without regulatory overreach.

      • I don’t think the “market” determines the carbon sequestration of a particular “product.” It just determines the price for that amount of carbon sequestration. (But this isn’t something I studied in economics school.)

        (I’m sure we all agree what “regulatory overreach” would be. Not.)

        • No, the carbon market determines what farmers will be paid for what practices. My point being that that is up to the people running the market. So the USDA is helping farmers understand what they have to do. Here’s a nice article by Extension folks in Texas. (Thank you TAMU!)

          “The CCX has established guidelines for participating in a carbon sequestration program through crop production, rangeland management, and/or afforestation. One of the most restrictive requirements for agriculturists to participate in the CCX market is that an entering group must represent a minimum of 10,000 tonnes of CO2 e. A contract of that size would require a cropland farmer to have about 25,000 acres, making this option impractical because few farmers have that much acreage.

          A practical alternative for most producers involves the use of an aggregator, which is an entity that pools, or aggregates, producers. An aggregator would act like the “county elevator” for the carbon credits marketplace. An aggregator combines carbon credits from agricultural offset projects initiated by farmers, ranchers, and private forest owners. For a list of authorized aggregators visit”

  5. We might be talking past each other. The question that has come up here is what forestry practices conserve carbon better, or how much carbon do you get from X vs Y. To go with the farming example, someone has to figure out the “tonnes of CO2” per acre from a particular farming practice. That’s a science question, not an economic (market) question. Back to forestry, USDA would have to “establish guidelines” for forest management (beyond just “afforestation”).

    • Yes, we’re definitely talking past each other. I wasn’t talking about the broader question of what forestry practices conserve carbon better.

      I was only talking about the bill that USDA would help farmers and forest owners get access to carbon markets. People who run the markets, not the USDA determine how much to pay folks. I’m sure they use science to determine that but let’s not forget there is not one “science” it’s pretty controversial. Still the market has to pick a lane, and each carbon market does so. For example, California has a carbon market. They figured out a method to pay rice farmers If the feds had a carbon market, then USDA and EPA would probably bureaucratically duke it out to determine what the guidelines were. But since they don’t, no federal government agency makes the call.

      Again, USDA is not holding the cards in any carbon market. Here’s an analogy.. USDA tries to get other countries to buy our stuff. They tell farmers what those markets want and tell the other countries what our farmers produce. They don’t determine what other countries want.


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