How'd They Do That?: Poison Ivy and Carbon Dioxide Studies

When I was visiting BoingBoing last spring, I told y'all about some research being done by Lewis Ziska from the USDA and Jackie Mohan from the University of Georgia on how poison ivy responds to rising levels of carbon dioxide in the atmosphere. (Answer: In a way that kind of sucks for people.)

What I didn't tell you was how the scientists figured out that CO2 makes ivy grow incredibly fast, and problematically poisonous. While some of the evidence comes from controlled studies done in a tidy, little lab, there's more to it than that.

These look a bit like high-voltage electricity transmission towers, or a Stonehenge-style monument built for some forest-dwelling version of Burning Man. Suffice to say, they are neither. Instead, they're actually giant structures of PVC pipe that Ziska, Mohan and their colleagues built to test the effects of CO2 on wild forest. The base rings are a 100 feet in diameter and vertical piping goes up to the very top of the forest canopy. Six towers total, in use from 1998 until 2004. Three blowing air. And three blowing a heady mix of air and carbon dioxide that pumped parts of the forest up to the ambient CO2 levels predicted for the year 2050.

And that was how the team learned something really neat. When I posted about this research before, somebody here asked whether other plants, besides poison ivy, got the same growth spurt from CO2 exposure. At the time, I didn't know. But talking to Mohan more, I found out that there's at least some basis for comparison. In particular, let's talk trees, turkey.

Both trees and poison ivy grew faster, when exposed to higher concentrations of CO2, than their oxygen-only counterparts. But poison ivy grew faster than the trees--150% faster, in fact, compared to a 20% increase in tree growth. The difference, according to Jackie Mohan, is that poison ivy, like all vines, is a bit lazy.

"Vines don't need to devote so much of their CO2 resources to growing these big, woody trunks," she says. "Instead, they can devote that to growing more green leaves, which increase photosynthesis some more. And it becomes a cycle."

This study was the first time the effects of CO2 had been researched like this in the wild. The next step will be to see how the growth of poison ivy differs between rural areas and cities, where CO2 levels are naturally higher thanks to a higher concentration of cars and industrial pollution. Mohan is working on that now. It's too early to tell, but she expects to find that the urban ivy is bigger and tougher than its country mouse cousin.

All images courtesy Jackie Mohan and Duke University.


  1. So, i wonder if its possible for the paper industry to speed up tree growth to counter their resource use more effectively by pumping CO2 into the area(s) where they grow trees, and more importantly, is there a point where the oxygen produced by the trees factoring in accelerated growth is greater than the CO2 being pumped in?

    Could increasing and targeting the production of what we were so worried about having too much of in fact protect us from having a CO2 overload?

    1. That’s a great idea. lets let corporations who care SO MUCH about the environment literally pump tons more CO2 into our atmosphere.

  2. I don’t presume to know enough about botany to be sure of this myself, so I’ll just ask an open question:

    Wouldn’t this imply that rising CO2 concentrations would, in turn, encourage heightened growth of the kinds of plants which would consume that C02 more rapidly and efficiently than trees would? Would that matter? Would a global flourishing growth of vines, shrubs, and other non-woody plants help boost woodland absorption of CO2?

    Setting aside for a moment the harm this would do to ecosystem stability, it is at least some comfort to think that plant life might respond in a way which could contribute a balancing effect.

    (sidenote: previewing comments before posting them is currently leaving me unable to submit them.)

    1. Keep in mind that more than 80% of CO2 is turned into O2 by algae and not trees/shrubs/grass/whatever. If they did this study on algae, the results might be different. Higher concentrations of CO2 might cause the lake to completely stagnate, killing the fish and such in it.

  3. “Could increasing and targeting the production of what we were so worried about having too much of in fact protect us from having a CO2 overload?”

    Except we’re deforesting so fast that a bit of extra growth in other areas can’t offset it quickly enough. Also they don’t indicate how much of the extra CO2 wasn’t absorbed so added to the problem too (at least on a larger scale it would.)

    1. It is so funny to read these comments about deforestation. First off, trees are a renewable resource. The big timber industry grows their own trees to turn into paper and lumber. Do you really think that just any old tree or shrub can be used to make paper?
      Rates of deforestation are myths. Now, for the extremely stupid amongst you: I am NOT saying that deforestation NEVER HAPPENS.. sure it does. It happens every time the timber industry cuts down one of their forests to make paper, then plants it back to re-harvest in another 20 years. Remember, these are what we call renewable resources. If harvesting a crop is detrimental to our planet, you should go out and protest corn farmers. It all makes about the same amount of sense.

      1. Now, for the extremely stupid amongst you: I am NOT saying that deforestation NEVER HAPPENS.. sure it does. It happens every time the timber industry cuts down one of their forests to make paper, then plants it back to re-harvest in another 20 years. Remember, these are what we call renewable resources.

        Perhaps you are unaware that a forest consists of more than neat rows of identical trees. Tree plantations are to forests what potatoes, potatoes and nothing but potatoes is to a balanced diet. Next time you call someone stupid, take that piece of timber out of your own eye first.

        1. This.

          And also, only the very responsible ones actually reforest the area- there are still many in places like South America that still use the slash&burn methods to open up land for growing crops (including corn that is used for ethanol, not food).

  4. CO2 helps plant growth for sure, and IIRC the mechanism of action has a lot to do with allowing plants to keep their stomata more closed, so they lose less moisture to the air.

    Unfortunately, I don’t think it’s enough of a negative feedback to bring the atmospheric CO2 levels back down. It does mean that some agricultural areas can benefit from increased CO2, though.

  5. Instead of using the trees to make paper.. why don’t we figure out how to make paper out of the poison ivy? Think of the possibilities! Oh wait.. nevermind. :)

  6. @ 2

    yeah, it’s a negative feedback. my understanding (from talking with ecology professors) is that whether or not this can offset global warming is not known.

    there are others: increased temp leads to more evaporation and more cloud cover. clouds are nice and reflective. another negative feedback. but, again, it’s not known where the thing (our planet) will stabilize.

  7. @querent

    Stability will probably come some time after famine, disease and war over dwindling resources reduces human population to the point where it won’t matter.

  8. @ AirPillo

    The problem with what you’re saying is in the long term sequestration of the carbon. Trees live a long time and thus the carbon they use is kept out of the air for a long period. Vegetation such as poison ivy dies and decomposes much more quickly, returning the carbon to the atmosphere in a short period.

  9. I believe this is the first study of CO2 effects in forests, but I previously read about a related study. This study found that plants grow faster for a time, but after a while their growth slows. The conclusion was that other nutrients, such as nitrogen fixed in the soil, become a limiting factor. The rate of replenishment of the soil’s nutrients must be increased in order to sustain the CO2-induced growth.

  10. @wackyxaky you’re correct about the sequestration issue. But I think that’s why it’s even more important to be developing things like biomass conversion to replace coal or wood burning for energy. Ivy and scrub plants grow fast, and can be harvested fast.

  11. I can’t see how increased CO2 levels could be a boon; in fact, I find this study to be more ominous more than anything. Vines don’t waste their time making woody trunks, they put their energy into climbing, and usually suffocating, the forest’s ladders to sunshine: trees. They compete for sun, water, and nutrients. At a rate of 150% faster growth, they could be tree-eaters, like kudzu.

  12. @airpillo: the vines could absorb greater CO2 but all of it would then be released at decomposition. So greater plant use of CO2 isn’t a sink, i.e., won’t permanently sequester CO2 and make a net difference in global levels.
    The oil/coal/etc we burn is sequestered carbon from plant materials buried during the Carboniferous period.
    (funny to think we are releasing all this carbon now, when the planet dodged a bullet when it was buried so long ago)
    re: botany, a great book is The Emerald Planet: How Plants Changed Earth’s History by David Beerling.

  13. Quote: “In particular, let’s talk trees, turkey”

    For a moment there, I was really hoping you’d tell us that CO2 held the promise of ginormous cluckers this Thanksgiving.

  14. Plants have to respire at night, meaning they have to take in O2 and emit CO2. So the idea that more C02 is better is pretty flawed. Plus every time you cut down a tree it releases a fair amount of CO2.

  15. “A Stonehenge-style monument built for some forest-dwelling version of Burning Man”…wait, these are a: disused and b: on public land?!?!?!

  16. You should grow that stuff all around your cities, should be harvestable for something? And it cleans CO2 right?

    Call me a dumb ass but it sounds great to me, something fast growing that sucks up CO2 and can be used for pellets, paper or whatever..
    U got genetics, remove the poison gene and overgrow the cities ;)
    green lovely green..

Comments are closed.