Monday, August 29, 2005

Trees Don't Suck up Carbon Dioxide as Hoped

Though not related to this thread, but have you seen this Trees don't suck up carbon dioxide as hoped?
Even though the gist of the article is that trees do not sequester more CO2 with higher concentrations in the atmosphere, it stated "It also remains to be seen whether a fraction of all this extra carbon might be stored in the soil rather than in the trees. If so, there may still be cause to think that forests will suck up more carbon dioxide in a warming world."
My questions on this report is what happens to extra carbon in the ground? And secondly this appears that CO2 is not a limiting factor in these areas, but could this be a limiting factor in other locations? What I posit is that higher and the highest elevations could find dramatic increases in sequestering of CO2 (and thusly growth). In Alaska trees grow tall with little foilage or width, could this change?

And now for something completely different. Responses from my inquiries.
I hope that the responders do not mind me reprinting at this time their remarks.

The first is from The Commons Blog:

What happens to extra carbon in the ground?
It is stored. Think of water in a river. There is water input through rain, and output to the sea. Each water molecule stays in the river only for a while, but there is always water. Rivers store water. If you increase rain quantity you get more water "stored" in the river (flow increases). Of course there will be less water somewhere else (say, in glaciers). The same for soil. If you increase carbon inputs more than you increase outputs you get more carbon stored in the soil, and less carbon somewhere else (say, in the air).
Could CO2 be a limiting factor in other locations?
Yes, CO2 may be more limiting where the supply of phosphorus, nitrogen, etc., is greater, and maybe at those places increased CO2 may have a larger effect on plant growth. The case of water is more complex because when plants get CO2 they loose water (both cross the plant "skin" through the same pores). Increased CO2 in the air may help plants save more water, and thus grow better, because they have to open the pores less often to get the same amount of CO2. This positive effect of increased CO2 may be more important in more arid places.
For the other questions I don't know the answer.
Posted by Biopolitical at August 29, 2005 05:57 PM

And this is from the blogger of RoguePundit:

The opening sentence of the Nature article is certainly an overstatement...editorially misleading. Maybe the Swiss were tooting their own horns some, but there are a number of similar experiments ongoing in other areas (in many instances for much longer) with different climates, mixes of trees, more acreage, etc. A few don't just test with increased CO2 levels. One small Swiss study is enough to invalidate all that data? Ridiculous. Some global warming theorists don't want any acceptable global warming solutions which include adjusting to existing CO2 levels, much less future increases...they only want to change how we live to reduce CO2 emissions.

Nevertheless, the Swiss data is interesting...and overall we we are still in the very early stages of such research.

- The results of such research have generally shown that as CO2 levels increase, most trees increase their CO2 absorption up to a point...they can only absorb so much. With the extra CO2, they are indeed growing faster, showing that CO2 availability has been a limiting factor, at least in growth speed. I know that with some vegetables, they grow faster with more CO2, but end up less nutritious. I haven't seen anything that shows if the CO2-fertilized trees grow better wood or not (just more), if the trees are more or less succeptible to insects and diseases, etc.

- For some trees, the extra CO2 makes no difference...maybe as CO2 levels have risen, those trees have already exceeded their capacity, and/or maybe they never evolved to absorb all the CO2 available--something else is limiting their growth.

- One piece of research I saw recently showed that the trees tested could absorb more CO2, so long as ozone levels didn't rise much. Above a certain ozone level, that became a limiting factor for growth versus the availability of CO2. Switzerland has acid rain problems, so it's possible that a pollutant is a limiter there. The Swiss test offered no way of determining that.

Generally, healthy soil does sequester carbon, but slowly overall (basically, the build-up of topsoil). But, there's a balance between what soil can uptake and what various microbes, etc. release (like swamps and their methane gas production...too many nutrients and/or not enough oxygen in the muck). In some areas, the land naturally builds soil depth and in some places not. In jungles, there is little topsoil, in fair part because 70 percent of what we consider topsoil isn't on the ground but on the trees. That's part of the reason so many plants grow on jungle tree limbs...that's where a fair percentage of the leaf litter, animal poop, mosses, etc. are. It's also one of several reasons that deforestation can have more adverse results in tropical forests.

There are so many answers to questions like this, many of which we don't know yet. But, we do know that 30 percent of the CO2 that man releases into the atmosphere remains to be accounted trees, mountains, soils, etc. are likely absorbing much of it. The ocean doesn't seem to be absorbing more than we already know about.

I think at high elevations and closer to the poles, several things will be at play. As higher elevations and latitudes get warmer and have more CO2, larger plant growth ought to replace the more stunted variety...some will be the same species growing more rapidly, while others will be outcompeted by interlopers. The end result would be increased carbon sequestration via the greater biomass. In certain places, maybe the temperature and CO2 changes will result in the mossing and growing over of exposed rocks (like granites), which chemically react with the air and sequester carbon. And in places with cold standing water and permafrost, the frigid temperatures have prevented a lot of the organic material from rotting. Additional warmth will change that, releasing more global warming gasses into the atmostphere (at least until the supply of nutrients has been exhausted). Et cetera. Ultimately, I agree that the colder climes will end up sequestering more carbon, but I doubt that will come close to offsetting the increased production.

Hope this wordy response helped some.


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