From: blagdon@engin.umich.edu (Kenneth James Clark )
Subject: Re: Soil Building (was: Re: Libertarians & the environment)
Date: Thu, 23 Jul 92 14:42:19 EDT
Organization: University of Michigan Engineering, Ann Arbor

In article <92205.123628MEK104@psuvm.psu.edu> MEK104@psuvm.psu.edu writes:
>
>Studies on tree physiology have demonstrated that carbon fixation rates (ie
>photosynthesis) generally increases with increasing CO2 concentration, to a
>point.The greatest carbon sink in any forest is the vegetation, particularly
>the woody vegetation.  When a tree falls over, wood munching critters injest
>the carbonand release much of it through respiration.  Insect frass only
>contributes very little to the organic material in soil.  Most of it is
>vegetative in origin.

I can think of a large number of the biggest forests in the world where
the vast majority of the carbon is *not* stored in the vegetation.  Hint:
You burn part of one of them in your gas tank.  

You need to qualify your statement to read "in any young forest".  I know
you don't want to, but the biggest amount of organic matter in middle
age and old forests is in the soil (nope, didn't say old-growth, doesn't
have to be old growth to be old).  'Wood munching critters' ingest much
of the carbon and release some of it into the atmosphere through
respiration.  Much more of it remains on the forest floor, and a great
deal of very old organic material gets buried year after year in this 
process.  This is soil building.

>When trees are cut, not all of the carbon in those trees is released
>immediately because much of the wood goes into structures, etc.  The problem
>is not with harvesting trees, the problem is with decreasing forested area,
>like in the tropics, which ultimately decreases the volume of the carbon
>sink.  Cutting trees and decreasing forested area are not necessarily
>synonymous.

This is true, but not all of the carbon in the trees that fall and
rot is released immediately either.  The wood you remove provides no
nutrients to the soil, however, which slowly depletes the soil.  The tree
rotting in the woods dumps all its nutrients back into the soil.  Since
trees produce more nutrients than they get from the soil (minerals from
sub-soils, carbon from the atmosphere, energy to produce cellulose from
photosynthesis), if left alone, a forest produces an extra amount
of soil each year.  When you start removing trees, you alter this process.
At some point, you reach an equilibrium (I don't know anyone who claims
to be able to calculate this point).  Clear-cutting tilts the scale
as far as possible to the soil-depletion side.

My point in all this is that the trees themselves are only a short-term
carbon sink.  The soil is where the real carbon stores are kept, and 
taking too much forest cover is a triple loss because you remove the
carbon storage machinery (the trees), you expose the biggest part of
the carbon bank to increased oxidation (the soil), and you decrease
the ecosystem's ability to produce more carbon-fixing machinery (by
depleting the soil).  If you're removing few enough trees that the soil's
integrity is maintained, you're fine.  If you take too many trees,
you're starting to hang yourself.

Ken