Tropical rainforest is often on leached soil where most of the
nutrients are actually in the trees. Saying that this environment
doesn't accumulated soil and therefore no forest will do so does not
necessarily follow. Particularly where temperate forests were
cleared for crop land you can certainly increase the amount of
carbon stored by converting them to pasture or back to forest. But
your point about reaching a maximum and then not storing any more is
correct.

Citation, please.


Note that we were talking about changes to land use not sequestering carbon
in less decomposable forms. I was told the amount that can be stored has
limits in a course by Dr Judi Earl who put me on to Dr Christine Jones. The
latter is the local guru on agricultural carbon sequestration. The reason
given is that as decomposable carbon builds up the microbes that break it
down also build up until the rate they are breaking down reaches the rate of
build-up, in other words an equilibrium is reached. The position of the
equilibrium depends on the land use and methods but you will still get one
sooner or later. This is ignoring the carbon stored above ground in forests
etc but you can see that it also has a maximum value depending on what is
grown.

Here is one quote:

"The capacity of soil to store decomposable organic carbon by
physical protection within micro-aggregates or other organomineral
complexes seems to be finite.
Once these complexes are saturated any added decomposable
organic carbon cannot be protected from decomposition.
Even if this capacity has been severely depleted it can be resaturated
rapidly (e.g. within 30 years by growing pasture)."

Which is from he

http://www.amazingcarbon.com/PDF/Lei...N_ARMIDALE.pdf

This site

http://www.amazingcarbon.com

has a huge amount of material on this topic. I haven't read it all. If you
also google on:

carbon sequestration "christine jones" site:.au

you will get much more. She is of the view that paying farmers to do
sequestration is a solution to climate change. I think we must try many
solutions because until you try you don't know for sure what the effect will
be and also there are political, economic and social limits on the extent
that any given solution can be adopted thus we are likely to need a
multi-pronged approach to succeed.

Also I would not want to push only sequestration solutions because the
fossil fuel industry will try to seize on any method of dealing with climate
change (eg "clean coal") as long as it allows them to keep on burning and
that is very undesirable for many reasons apart from the increase in
atmospheric CO2.

David