How much CO2 a forest is gaining or losing? 1

[0707]

"One major difficulty in answering how much CO2 a forest is gaining or losing is that forests both take up CO2 (through photosynthesis) during the sunlight well as release it (through respiration) at night; it is the balance which decides whether a forest is a net source or store of carbon. Scientists have had to come up with some very ingenious tricks to measure exactly how much CO2 a forest is breathing in and out."

What will happens to carbon and methane release of died plants?

Luis

 

[SomptingGuy]

I would say that if trees are growing, there must be a net conversion of carbon into wood.

 

[0707]

And during summer time there is lots of conversion of wood into carbon through the fires.

 

[zdas04]

I'm not sure I'm buying that "if trees are growing, there must be a net conversion of carbon into wood". If the tree takes in a tonne of air, adds 20 kg of mass to its body, and "exhales" the remaining 980 kg, it is not a slam dunk that more carbon is sequestered than is emitted. That is why "Scientists have had to come up with some very ingenious tricks to measure exactly how much CO2 a forest is breathing in and out". Both rapid oxidation (fires) and slow oxidation (decomposition) put very large amounts of carbon into the air and I think that it is a good thing that talented scientists without an agenda are trying to put some real science into it.

The science of climates and climate change are both growth areas today, but as recently as 50 years ago they were backwater fields that had zero glamour. It truly is an infant field and I think that assuming facts not in evidence is the kind of wishful thinking that we should leave to the media.

David

 

[SomptingGuy]

Uh? So what are trees made from? Whatever it is it doesn't come through their roots. The roots soak up H2O, the leaves do cool things with CO2. Whatever hapened to the laws of mass conservation?

 

[SomptingGuy]

I was going to post that my non-scientific friends somehow thing that the wood-mass in trees somwhow comes from the ground rather than from CO2 in the air. It seems some engineers need to be taught too.

 

[SomptingGuy]

... maybe we should be encouraging more forrests to make coal?

 

[GregLocock]

I'm reasonably sure that while they are alive trees are a net absorber of carbon. But once they are dead that carbon is dispersed back into the environment. Once in a while some gets sequestered underground as coal or oil or diamonds, otherwise it just forms part of the general global carbon cycle. So from a macro level, I doubt trees have much of a first order effect on carbon, unless you are continually expanding the forests.

BUT

If you burn wood, or build your house out of wood, then that will affect the carbon cycle, because the alternatives (coal, oil, concrete,steel) are energy intensive and the energy is often created by burning previously sequestered carbon. Cement is made by burning limestone, that is also returning sequestered carbon to the carbon cycle.

So, if you have lots of trees, people will tend to use them in preference to the sequestered carbon sources.

That is not to say that I agree that more carbon in the carbon cycle is a bad thing, but that is not what the OP asked.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[YoungTurk]

A star for SomptingGuy! Carbon doesn't come up through the roots, so it must come from the air.

To elaborate, since wood is composed primarily of cellulose, which is a hydrocarbon, the dry mass of a chunk of wood is largely carbon. C6H10O5 makes about 45% by my calculation. I think the difficulty for scientists is in "determining exactly the amount of carbon..." the net amount isn't so difficult to determine.

Of course if you burn or otherwise release that carbon back into the atmosphere, you'll lose a significant part of the sequested carbon. You'll never go negative, of course. Thats why biofuel is often referred to as "zero net emissions".

Well, Greg must type faster than me! Cheers

 

[YoungTurk]

An anecdote from my days at the FPL (Forest Products Lab):

My boss was always working on bringing in more research bucks, and as such had several canned eyebrow lifters for our dog and pony shows. Our nitch was coming up with new uses for wood fiber, i.e. trees and brush that couldn't be used for lumber. He liked to point out that these small trees sequestered carbon at a faster rate than the older, more valuable timber trees and as such were an obvious choice for carbon sequestration, a side affect many people don't think of when it comes to forest products. One of the first times I heard him point this out, I asked him later "Well, doesn't it all end up back in the cycle anyhow, what with decomposition and incineration and all?" He gave me quite a look, and then quietly said, "Thats why all my paper goes in the trash."

I still try to recycle my paper (must be the hippie in me) but I can't get too uptight about it because that always pops into my mind when some paper products find there way in the bin.

 

[rb1957]

here's a dumb idea ...
animals (like humans) intake O2 and expell CO2 (amoung other things)
something better be making up for this (otherwise we'd've run out of O2 awile ago).
i've always understood that vegetation (like trees) intake CO2 and expell O2 ...

 

[CorBlimeyLimey]

... but only during the day.

 

[rb1957]

animals consume O2 and produce CO2, yes ?

if vegetation is not a nett depoistor of O2 then what is, since we animals are a nett consumer ?

if vegetation is a nett depoistor of O2, doesn't this mean that they are also a nett consumer of CO2 ? otherwise what is, since both animals and vegetables would be nett depoistors ?

so vegetation can consume O2 at night, but they produce more during the day, and the opposite for CO2.

wasn't President Regan (sp?) who said (wrongly) that pollution was caused by trees ?

 

[KENAT]

Let's cut all the trees down and bury them in old coal mines or mash them to fine pulp and inject it in old oil wells.

Then it’s sequestered if not quite permanently then for quite a while.

 

[LCruiser]

A mature forest, like the Amazon *was*, are neutral. A young or developing forest obviously takes in more carbon than it (or the ground around it) expels because it's getting bigger.

The caveat to all this is that with increasing CO2 the equlibrium rate for forests is of greater mass, so even a mature forest will be taking in CO2. Since increased CO2 reduces water demand, that's even more true.

 

[GregLocock]

" Since increased CO2 reduces water demand, that's even more true."

Can you expand on that?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[YoungTurk]

I think LCruiser is referring to some theories of tree/forest growth that correlate increased CO2 supply with decreased H20 consumption and increased growth rate. Seemed to me like these were under considerable debate amongst the tree scholars (thats not me), though.

The root idea of general forest size seems sound, however, it doesn't seem to account for potential carbon stores such as bogs or similar.

Something to consider in the carbon cycle conversation: the ocean has been the primary absorber of industrial CO2 (and possibly also exceed CO2 uptake land/forests throughout history). Us landlubbers (that me) tend to forget the ocean covers most of the planet.

Two methods of aquatic absorbtion:

1)dissolved CO2 in the water
2)CO2 uptake by microorganisms

#1 is responsible for the majority of the idustrial CO2 uptake, but we may be approaching saturation in the upper layers of the ocean, at which point uptake will slow drastically. This is/was our buffer.

#2 is likely the source of most oil reserves, as the organisms die they drift down the the bottom and form layers of carbon rich sediment. This process is not likely quick enough to remove industrial emissions. Can/should this process be stimulated?

 

[LCruiser]

The stomata of a plant open to capture CO2, and while they're open they exhale H20. The higher the concentration of CO2 the less time the stomata need to be open, so the less H20 evaporates.