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Post by steve on Mar 7, 2009 12:21:45 GMT
Concurring with what hiddigeigei says, warmer temperatures would speed up metabolisation in soils thereby releasing more of the stored carbon.
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Post by nautonnier on Mar 7, 2009 12:23:09 GMT
3. Mature forests are net emitters of CO2TWO COMMENTS: All living cells respire continually (break down carbohydrate into water and CO2). A temporate mature tree photosynthesizes to produce and replace leaves, maintain its living structure, and store sugars for nights and winter. Much production is lost when it drops its leaves, but it is still a net producer of carbohydrates unless it is dying. The leaves, litter, frass, pollen, seeds, etc. are mostly (but not entirely) metabolized by bacteria, fungi, and inverts; but it was all fixed by the tree from CO2 originally, so the mature forest is still a net collector of atmospheric carbon. When the Shenandoah Valley was first seen by Europeans, it was nearly treeless. The Indians burnt it periodically to provide pasture for their large game animals. Define your logic - the tree has stopped growing and : "The leaves, litter, frass, pollen, seeds, etc. are mostly (but not entirely) metabolized by bacteria, fungi, and inverts; but it was all fixed by the tree from CO2 originally, so the mature forest is still a net collector of atmospheric carbon." So the CO 2 that was fixed during the year has now been released back into the atmosphere during the fall/autumn - while the respiration continually releases CO 2 into the atmosphere. You will admit that the amount of Carbon 'fixed' by a mature deciduous tree is likely to be less than its respiration. The reduction in the minimal radiative forcing by fixing that small amount of carbon will be dwarfed by the radiative forcing effect of turning ground water into water vapor due to continual transpiration for the entire life of the tree. Note: I have yet to see any real-world validation that CO2 has any noticeable impact on atmospheric temperatures - certainly water vapor does and even the AGW proponents rely on water vapor's forcing effects as they know that CO2 alone is insufficient.
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Post by hiddigeigei on Mar 7, 2009 18:29:27 GMT
A mature tree doesn't "stop growing." It just slows down. It still produces leaves, twigs, replacement branches, roots, growth rings (lignins, cellulose, sugars, etc. all fixed from CO2 either from its own respiration or from the atmosphere). If it doesn't fix as much CO2 as it respires, it dies. There's a difference between a mature tree and a dying tree. Mature forests tend to increase a layer of duff which is not entirely metabolized. This was particularly true in North America before the Europeans introduced the earthworm. It is true that fast-growing immature trees like those farmed for paper probably sequester more carbon once they reach a certain size, but mature forests fix more carbon than they release on a yearly basis.
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Post by poitsplace on Mar 7, 2009 18:38:00 GMT
It is true that fast-growing immature trees like those farmed for paper probably sequester more carbon once they reach a certain size, but mature forests fix more carbon than they release on a yearly basis. Oops...as soon as you say mature FORRESTS it starts to get pretty close to zero. All but the tiniest portions of these enormous trees are returned to the atmosphere as CO2 after their deaths. Mature forrests sequester very little carbon since they've reached equilibrium. (dead and dying v/s growing) ...but still as you observed, sequestering carbon. Just negligible amounts.
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Post by hiddigeigei on Mar 7, 2009 19:39:23 GMT
Not to qibble, but if a giant Sequoia 320 feet tall with a diameter of 25 feet puts on a 1/16" growth ring in a year, that's hardly a negligible amount.
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Post by poitsplace on Mar 7, 2009 22:51:15 GMT
Not to qibble, but if a giant Sequoia 320 feet tall with a diameter of 25 feet puts on a 1/16" growth ring in a year, that's hardly a negligible amount. That is once again... a single tree. A "climax" (mature) forest has reached equilibrium. There is just as much death as there is growth. Each living tree removes CO2 from the air to be sure but each dead and dying tree is putting their stored CO2 back out into the environment. The only carbon sequestered by a mature forrest is whatever gets stuck, unmetabolized, in the soil.
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Post by nautonnier on Mar 7, 2009 23:31:26 GMT
Not to qibble, but if a giant Sequoia 320 feet tall with a diameter of 25 feet puts on a 1/16" growth ring in a year, that's hardly a negligible amount. And there are lots of 320 ft tall sequoia - you have to be really careful to avoid hitting them in Penge and Podunk
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Post by jorgekafkazar on Mar 8, 2009 5:32:54 GMT
Concurring with what hiddigeigei says, warmer temperatures would speed up metabolisation in soils thereby releasing more of the stored carbon. And, of course, those same warmer temperatures would speed up the growth of the trees, thereby fixing more carbon. Not to mention the fact that metabolization of forest litter would release CO², which, as we all know, also increases the growth rate of trees. Further, the dropped leaves themselves insulate the trees' root systems from winter temperatures, and their metabolization further warms and protects the roots. The benefits go on and on.
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Post by jorgekafkazar on Mar 8, 2009 5:39:06 GMT
A mature tree doesn't "stop growing." It just slows down. It still produces leaves, twigs, replacement branches, roots, growth rings (lignins, cellulose, sugars, etc. all fixed from CO2 either from its own respiration or from the atmosphere). If it doesn't fix as much CO2 as it respires, it dies. There's a difference between a mature tree and a dying tree. Mature forests tend to increase a layer of duff which is not entirely metabolized. This was particularly true in North America before the Europeans introduced the earthworm. It is true that fast-growing immature trees like those farmed for paper probably sequester more carbon once they reach a certain size, but mature forests fix more carbon than they release on a yearly basis. Yes, that makes sense. if you see a forest, you see sequestered carbon.
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Post by kiwistonewall on Mar 8, 2009 7:50:46 GMT
If you see a newsagent, a timber home, etc etc you see sequestered carbon! ;D (I have bookshelves of sequestered carbon)
More is sequestered if you chop those trees down & let new ones grow.
(There are good reasons to preserve habitat, but sequestering carbon isn't one of them!)
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Post by hiddigeigei on Mar 10, 2009 13:54:21 GMT
I agree that sequestering carbon is not a valid reason to preserve mature forests (the more CO2 the merrier, as far as I'm concerned), but the question was whether mature forests are net CO2 emitters. They aren't, and they haven't reach an equilibrium either. Even fast-growing tree farms such as those raised for paper have to approach harvesting size before the fix as much carbon as a mature forest. The gaint sequoia was an extreme example, I admit; but by rough estimate that tree produces about 750 board feet of lumber per year in its trunk alone. Part of the litter it produces contributes organic matter to the soil. Most mature forests have an understory (ferns, lichens, and moss, at least) that recycle CO2. Insect metabolism produces chitin; a pretty durable material. Higher animals produce bone that degrades slowly. If you want to see sequestered carbon, take a look at the White Cliffs of Dover or Rügen or any limestone mountain!
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Post by nautonnier on Mar 11, 2009 0:33:47 GMT
I agree that sequestering carbon is not a valid reason to preserve mature forests (the more CO2 the merrier, as far as I'm concerned), but the question was whether mature forests are net CO2 emitters. They aren't, and they haven't reach an equilibrium either. Even fast-growing tree farms such as those raised for paper have to approach harvesting size before the fix as much carbon as a mature forest. The gaint sequoia was an extreme example, I admit; but by rough estimate that tree produces about 750 board feet of lumber per year in its trunk alone. Part of the litter it produces contributes organic matter to the soil. Most mature forests have an understory (ferns, lichens, and moss, at least) that recycle CO2. Insect metabolism produces chitin; a pretty durable material. Higher animals produce bone that degrades slowly. If you want to see sequestered carbon, take a look at the White Cliffs of Dover or Rügen or any limestone mountain! OK so you won't believe me ... perhaps this www.newscientist.com/article/mg20126964.100-ancient-felling-may-explain-carbonsink-forests.html"In theory, mature forests should be carbon-neutral - releasing as much as they absorb as the total locked up in trees remains constant."The article goes on to explain that the forests are recovering from historical 'slash and burn' and so are sequestering carbon until they have fully recovered.
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Post by kiwistonewall on Mar 11, 2009 1:17:42 GMT
"Mature" forests are very rare - when you factor in Volcanic activity, forest fires and other large scale events (i.e Ice ages), few forests have the required several thousand years to reach maturity.
Many trees can grow for 1000's of years (NZ Kauri for one) but tend to get beaten by geology (buried in swamps when the land sinks, etc etc)
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Post by hiddigeigei on Mar 11, 2009 19:50:53 GMT
Perhaps we are talking about different things. I interpreted the term "mature forest" as a "climax community" inwhich plant succession had more or less ended and the ratio of tree and plant species is fairly constantly maintained. Even if a "mature forest" is defined as one where tree growth and death has reached an equilibrium, such a forest will produce more air-borne carbon gasses and aerosols than simply CO2. To say a living forest produces more CO2 than it fixes is like saying a community of human adults burn more calories physiologically than they consume.
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Post by icefisher on Mar 14, 2009 18:30:03 GMT
"Mature" forests are very rare - when you factor in Volcanic activity, forest fires and other large scale events (i.e Ice ages), few forests have the required several thousand years to reach maturity. Many trees can grow for 1000's of years (NZ Kauri for one) but tend to get beaten by geology (buried in swamps when the land sinks, etc etc) Bingo! Mature forests in theory are carbon neutral. But as one poster has pointed out there are continual carbon sequesterization going on on the forest floor. Its very noticeable when you visit a mature redwood forest you find a top soil sometimes meters thick filled with wood fibre. It might be unique to the anti-rot nature of redwoods but a completely mature redwood forest if there is any is really really old. The fact is carbon sequesterization in a forest is a curve starting from zero reaching af maximum rate of carbon sequesterization, then the rate gradually declines towards zero though short of a disaster for the forest, fire, disease, etc. it probably never actually reaches zero. But despite that there is an opportunity for carbon sequesterization from cutting forests. But I am for sequestering it based upon demand for products not biochar.
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