[Terrapreta] Life cycle of forest fire char?

[Duane Pendergast]

            David,

 

It seems many fires kill even large trees and leave them standing up in this
part of the continent. Forests have been and are burned quite regularly. The
possible role of naturally occurring fires in producing char and building
soil seems something we should know more about.

 

http://www.computare.org/Support%20documents/Letters/Letters%202003/Forest%2
0Fire%2003_08.htm

 

Duane

 

-----Original Message-----
From: terrapreta-bounces at bioenergylists.org
[mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of David Yarrow
Sent: January 30, 2008 2:11 AM
To: terrapreta at bioenergylists.org
Subject: Re: [Terrapreta] Life cycle of forest fire char?

 

not all forest fires burn the same.  most burn hot and fast into ash.  some
burn slow and smolder, leaving behind some char amid the ash.  differences
are due to variations in weather conditions and species mixes.  dry pine
burns hot and fast.  moist hardwoods tend to burn slower, smolder and char.
generally, these last few years, we see more hot, fast fires.  and lots more
megafires that rapidly burn tens and hundreds of thousands of acres.
generally in any fire, most undergrowth and smaller trees are reduced to
ash; char is the lesser, less frequent outcome.

 

a few years ago we did an ancient forest survey in a deep, steep, wide
ravine west of schenectady, NY.  we discovered there were few elder trees
except a few fire resistant oaks.  as near as we could determine by direct
site study, about 80-120 years ago, a fire swept the ravine of most young
trees and many species.  in studying trunk cores extracted with an increment
borer from larger, older trees, tree rings revealed a layer of char when the
tree was partially burned, scorched and charred on the outside, but not
killed.  eventually burn scars were encapsulated and overgrown, becoming
embedded in the trunk.

 

at another site a few miles nearer schenectady, we found 250+ year old oaks,
white pine and hemlocks, with a few large pitch pine, which seldom gets over
100 years.  one 2-foot diameter pitch pine was down lying across the trail,
so 4-inch thick cookies were chainsawed from the trunk.  we counted 120+
rings in the cookies; very old for a pitch pine.  to our surprise, the
inside of the trunk was cracked open in a cavity lined with char.  our best
guess is the tree was struck by lightning and ignited, but survived,
recovered, and in 50 years, encapsulated and sealed off the charred crack
split open by the lightning.

 

in any event, char isn't easily eroded by weather, corroded by chemistry, or
digested by biology, and thus does not break down and vanish from soil.
reduced carbon in char isn't degraded by normal natural processes.  with no
hydrogens, oxygens or other atoms (electron-enriched) attached, normal
degradation processes can't eat away at the carbon.  thus, unlike oxidized
ash and other combustion products, char won't disappear from soil, but
instead stays residents for decades, centuries and millennia.  this
long-term retention of charred carbon in soil is why archaeology is able to
use radiocarbon analysis to date ancient objects and sites.

 

in forest fire conditions, entire woody objects are seldom combusted into
char.  more usually, char only forms on woody surfaces.  in controlled
pyrolysis, temperature, oxygen and pressure are controlled to maximize char
production.  but it very rare to create such conditions in a forest fire.

----- Original Message ----- 

From: Green Waste Recycle Yard <mailto:info at GreenWasteRecycleYard.com>  

To: terrapreta at bioenergylists.org 

Sent: Tuesday, January 29, 2008 7:57 PM

Subject: [Terrapreta] Life cycle of forest fire char?

 

As their counterargument, they said that all the char from a forest fire was
essentially gone a few years later, therefore (in their view) it must have
been biodegraded as a nutrient. If true (that it is gone), I suggested that
most of it was removed by water run-off, but I actually don't know. So I'm
asking here. What happens to char produced by a forest fire?

 

1) Is it mostly not pure charcoal, and thus does get utilized as a nutrient?

2) Does it wash/blow away because it is on the surface?

3) Does it enter into the soil?

4) Does it actually "go away" as they claimed? Or is this just simplistic
observation on their part?

5) Some combination of the above, or other explanation?

 

No need to go into a detailed response if you can simply point me to
appropriate articles, etc instead.

 

There is going to be a lot of resistance from old school anti-burners, so it
is important to know how to answer their questions and help them reframe
their thinking.

 

TIA,

Bernie

 

 


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