Sunday, June 24, 2007

Forest fires

(This is a continuing part of the mob blog on the carbon cycle. Tamino at Open Mind is posting on the latest trends in atmospheric CO2 concentrations and Simon Donner at Maribo wants to tell you about where all the carbon goes.)

There is an ongoing discussion in our mob blog about the role of forest fires. Horatio Algeranon lit the incendiary device. Tamino picked it out as particularly interesting and re-published the comment. Eli was wondering if there was a way to get at this.

Because most of the combustion occurs at relatively low temperature (relative here is still high enough to cook bunnies and little deer plus the occasional house) where the system is very much NOT optimized for emissions, forest fires are huge sources of CO (carbon monoxide). This is also true of agricultural burning, whether to clear ground for farming, or to reduce crop stubble after a season. The AIRS instrument can also track CO as well as CO2

The above map from September 2002 shows the major agricultural burning going on in Amazonia, Africa and Indonesia. This burning is quite interesting, also being a major source of tropospheric ozone in the Southern Hemisphere. Mongabay has a spectacular series of false color images showing how the burning in Africa follows the seasons. SAFARI and EXPRESSO are two measurement campaigns that have given us more information on this.

However, back to the point. There are two videos that all mice should see. The first shows CO emissions at the 500mb level in August and September of 2005. The second shows CO emissions from the huge fires in Alaska in 2004. They occured from May to Sept. Eli is not sure what the calibration is on the last one so it is hard to compare. On the other hand we can look at the CO2 readings at Barrow Alaska, and see if there is a jump in the period of the fires

       Mar    Apr    May    June   July   Aug    Sept  
2003 381.44 381.43 382.21 380.76 371.00 364.74 368.28
2004 382.17 383.80 383.47 380.50 371.75 366.50 367.86
And we can do the same for Alert Station Canada which is downwind of the fires
       Mar    Apr    May    June   July   Aug    Sept
2003 380.90 381.39 382.38 381.02 373.78 367.97 368.55
2004 381.58 383.21 383.58 382.59 374.58 368.69 368.55
The jump, if any is well within the range of natural variability which can be gauged from the Mar and Apr reading. Seasonal variability is 12-15 ppm at these high latitudes. Anyone interested in more information can go the linked cdiac site.

On the other paw, the issue is not so simple. Forest fires put CO2 into the air from burning, but they also can decrease CO2 emissions from soils after the fire by among other things destroying ground cover.


Anonymous said...

I thought readers might be interested in my recently completed report on "Forests, Carbon & Global Warming."
Size 2 MB - File type MS Word

The report explains how climate change is likely to affect Pacific Northwest forests as well as how forest conservation and restoration may help mitigate climate change. The report also helps debunk some of the flawed arguments used by logging advocates.

Feel free to contact me if you have any comments/questions.

Doug Heiken

Anonymous said...

If you really want to get an impression of the distribution of antropogenic CO2 emissions you can use the spectral NOx proxy.

Anonymous said...

link to online Temis maps:

Tropospheric Emission Monitoring Internet Service

Tropospheric ozone (O3)
Nitrogen dioxide (NO2)
Formaldehyde (CH2O)
Sulphur dioxide
Cloud information
Long-range transport
Clear sky UV index
UV daily dose
Total ozone (O3)
Bromine monoxide(BrO)
Volcanic plume

EliRabett said...

Thanks for the link Hans. I'm going to add that site to my bookmarks. However, NOx is a measure of high temperature combustion without trapping or catalytic conversion. It arises in situations where the temperature is high enough that N2 thermally dissociates to N atoms which then react with O2 to form NOx.

NOx is the principle precursor to tropospheric ozone. It will be reduced relative to CO2 in any location where there are legislated ozone limitations. Thus California, the US and Europe have relatively low NO2/CO2 ratios and the industrial areas of China are huge.

Eli smells another post.

Anonymous said...

"Forest fires put CO2 into the air from burning, but they also can decrease [sic] CO2 emissions from soils after the fire by among other things destroying ground cover."

Don't you mean increase?

Reduced ground cover will reduce the extraction of CO2 from the air by plants, resulting in a net increase in atmospheric CO2 over pre-fire CO2.

Also, the paper you linked to says fire increases microbial respiration, pumping yet more CO2 into the air from the soil.

"The microbial respiration estimated after the fire is almost three times as high as that the calculated respiration before the fire. This finding indicates the post-fire condition may stimulate microbial respiration because of higher nutrients and substrates in remnant soils and enhanced soil temperature. The microbial respiration can be estimated 14.7 tC/ha in burned black spruce stands over a decade after the fire, suggesting burned black spruce forests in central Alaska are a crucial source of atmospheric CO2."

-- Horatio Algeranon

Anonymous said...

The video shows that the CO (and undoubtedly CO2 as well) is getting lofted (by virtue of the heat generated by the fire, among other things) high enough above ground level to get caught in the prevailing winds.

That might explain why you don't see a jump in downwind measurements of CO2 taken at ground level.

This is similar to the case of SO2 produced by midwestern power plants. Much of it does not have its effect at ground level until points well down wind (eg, in upstate NY)

-- Horatio Algeranon

Anonymous said...

Also, Barrow is north of the fires and the prevailing winds would take the emissions east.

Unknown said...


Check some statistics for

US wildfires

Alaskan Wildfires,

Canadian Wildfires,

and much more here.

By the way, the decreased soil respiration is interesting, though the results should not be extrapolated. To ma knowledge, at least according to research in the Czech Republic, the soli respiration increases after the fire…


Dano said...

Fire is an important process in that it results in nitrification and a resultant N flush that soil critters and flora require, as most forests are N-limited.

But the important thing is scale, as always in nature.

Immediately postfire, there is less respiration. As time passes, there may be increased soil respiration (R), depending upon fire severity - if there is a crust or glaze created from intense heat, precip won't penetrate and you get less soil R. The flush of growth after normal fires increases soil R as critters and flora do their work as a result of plant root processes. Conversely, soil and wood sequesters C, and fire kill slowly releases C, some to the atm, but the flush of new growth can sequester more C than is lost.

IOW, I consider Eli's statements to be generally correct.



guthrie said...

DAmmit DAno, your first sentence fits in with stuff about forest fires that never really made sense to me before.
Can you reccomend some reading material on this and related topics?

Dano said...

Sure g.

E-M Eli for a good address for me and we'll talk. If I can find my fire ecology text I'll scan for you, else I've got lots of things laying around here..



Anonymous said...

From the abstract, it seems that the paper seems to deal with CO2 released from "soil" (as opposed to the entire forest picture)

"The forest fire significantly decreased soil CO2 and N2O emissions, by at most 50%."

But what about the loss in the CO2 sink capacity due to the loss of living trees 9and other vegetation)?

I would expect a net increase in CO2 released following the fire from the forest as a whole. Loss of the trees and other vegetation to the fire undoubtedly significantly reduces the carbon sink that the forest represents. If you lose a tree that is taking a significant amount of CO2 out of the air, it obviously affects the overall balance sheet. And brand new growth is not going to compensate.

Perhaps they were actually measuring the overall affect (including the loss of the sink capacity due to loss of trees), but that is not at all clear from th abstract.

EliRabett said...

My impression is that mature forests are pretty much carbon neutral. A lot of the CO2 absorbed goes to leaves, and leaves fall and decay. Suffice it to say that the situation is complex with great opportunity to look foolish.

Anonymous said...

"great opportunity to look foolish."

The opportunity to look smart is like the chance of picking a prime number from a hat filled with all numbers.

The opportunity to look foolish is like the chance of picking any number from the hat filled with all numbers.

Dano said...

Trees grow at a rate plotted on a sigmoid curve. Once they reach a certain point all metabolism is maintenance and no longer is the fraction of metabolism that goes to growth larger than maintenance/respiration/reproduction. This is not to say they stop sending down yummies into the soil via their roots, but Eli is again generally correct. Thus the Ronald Reagan thing that we should cut down old-growth because young trees store "more" C.



guthrie said...

Thanks Dano, although I don't know much about forest fires, your comment actually made sense, rather than whatever I have picked up over the years from TV.
I can't seem to find Elis address, but my yahoo account is:
guthrie underscore stewart

EliRabett said...

Guthrie, I apologise, Dano said I should try and contact you, but I got tied up. You can reach me in the future at EliRabett2003 at yahoo dot com.

As soon as you and Dano make contact I will pull these comments down the Rabett hole.

Anonymous said...

I don't doubt that an old growth forest removes less carbon than a younger one from the atmosphere (may remove none)

I don't even doubt that an old growth forest stores less carbon than a younger one, as is shown on this nasa graphic.

But, most forests (in the US at least) are not old growth forests and initially, at least, there is a decrease in the net carbon taken out of the atmosphere per year when a large forest burns or is cut down. Eventually, it will be overcome (and the young forest will take out more carbon) but it may take years to overcome the difference.

I think one has to make a distinction between what happens over the long term and the short. The paper that Eli linked to is clearly talking about what happens immediately following a fire. Furthermore, it addresses the soil, so one can not conclude anything about the overall carbon budget from that piece of information alone.

From the NASA graphic, it is clear that if one wants to store the most carbon, it behooves one to have a regular (every few decades?) program of cutting so that one is maximizing the amount of carbon taken out (and presumably used for lumber, paper, etc)

EliRabett said...

Old growth refers to forests that have never been cut/burned since the year dot, more than a couple of hundred, maybe 500 years on the ground. Mature is a forest that displays wisdom, houses bunnies and deer in comfort, excludes Elmer Fudd and where most of the trees have achieved full growth and the ecology is stable, maybe 100 years old. Quibble, quibble.

Anonymous said...

Forgive me. I should have left out the "growth" part from "old growth" (since "old growth" has a specific meaning, as you point out) and stuck with the "old" vs "young" distinction referred to in the NASA graphic that I linked to (though it is not clear exactly what that means).

I don't disagree with the basic idea that a "young" forest removes more carbon per tree per year than a mature old forest (or more carbon is stored in a "young" forest than an old one), though just where the break-even line occurs is not clear and presumably depends on a great number of things), but the "low-growth forest" that exists immediately after a fire will almost certainly remove less CO2 from the air than the one that existed just before the fire.

In fact, it will take a certain amount of time for new seedlings to sprout and get established. The other thing that one has to consider, of course, is the severity of the fire and erosion. If the fire is severe enough, there may be significant erosion, which will prevent future growth. That is one of the rationales that has been put forth for not suppressing all fires and actually instigating controlled burns in some cases.

I would agree that this is all very complicated.

For example, if one were to attempt to maximize the amount of carbon removed from the atmosphere over the long term, how often would one cut and replant the forest? (and presumably use the wood for building and other purposes that essentially lock up the carbon over a long term)

Dano said...

if one were to attempt to maximize the amount of carbon removed from the atmosphere over the long term, how often would one cut and replant the forest? (and presumably use the wood for building and other purposes that essentially lock up the carbon over a long term)

This is a very complicated question. Each forest type has a different scale over which it regenerates from disturbance, goes thru successional stages and then reaches climax. For example, the climax Western Hemlock forest currently found in Western WA may or may not be 'ultimate' climax. But for our purposes, it is a climax forest with death for a tree expected from 400-750 years. BUT - the wood is poor for timber. So "maximizing" carbon would be to let the forest be.

But for human socioeconomic purposes, we need wood and must manage our timber. This is why there are distinct units called "National Forests", although there is wide variety of successional stages there too.

So, the short answer is that carbon is also stored in soil after plant death. so there is an additional factor to consider.



Anonymous said...

Thanks for interesting article.