Black Forest forests

[Heinz Hilbrecht <Hilbrecht@xxxxxxxxxxxx>]

Peter Wilf wrote:
>It's been my understanding, although this is far from my field of study, that
>the acidification of the Black Forest turned out to be the result not of acid
>rain, but of the historic practice of German foresters of removing nearly
>all fallen trunks from the forest. Base cations were thus permanently
>removed from the mineral cycle, acidifying the soil over time. As far as I
>know, this practice has been corrected and the health of the Black Forest
>is now improving.
>Can anyone bring me up to date?

There are various opinions among German students of the problem.
Interesting enough, there is a general correlation of topographic height
and unhealthy trees (as seen also in other areas). There is a lot of
evidence for the idea that car emissions help to create ozone which in turn
disturbs the respiration of the trees. The other component is the acid rain
and soil acidification which is caused by industrial emissions from outside
the Black forest. Acidification of the soil affects soil chemistry
(including nutrient and metal availability) and the biocenosis which
supports the trees (e.g. fungi, which are dramatically reduced in some
areas). Rocks in the Black Forest tend to be granites and gneisses which
are no good buffers against acids. The corresponding soil chemistry affects
the availability of base cations (there was a paper in one of the very
latest issues of the Scientific American on this).

The removal of trees is an economic practice which is common in all German
forests. This practice has been applied for hundreds of years and does not
correlate with the geographic pattern of unhealthy trees. It is partly
compensated by external nutrients which makes these forests appear more
like agricultural production areas than what you may consider a natural
forest. The widespread change in the practice of forest management ("leave
the forest like it is") finds its reasons in ecological considerations
which combine with economic motivations. A forest which evolves the natural
way (e.g. no monocultures, no removal of fallen trunks to support insect
communities) is the most stable against hazards (insects, storms,
acidification, etc.) and is the most productive in economic terms.
"Natural" or "ecologic" managment of forests is, therefore, an example
where ecologically correct behavior has its economic benefits.

I can not say that the Black Forest is improving (or not). There is a
practice to remove unhealthy trees because they are considered to support
mass occurrences of unwanted insects. Therefore, the government presents
statistical data on the forests (number of problematic trees) which does
not include the trees that have been taken out. The same kind of statistics
would classify somebody healthy whose lungs affected by cancer have been
successfully removed. From independant observations it is evident that much
of the forest has disappeared in certain areas. The mentioned article in
the Scientific American demonstrates why the problem is a long-term
problem. Observations over a few years (e.g. my personal experience) are
probably not significant.

Heinz Hilbrecht





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Geological Institute
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