[permaculture] "thirsty " trees....

Ute Bohnsack sustag at eircom.net
Wed Sep 11 20:50:58 EDT 2002

Hi Kirby,

Kirby Fry wrote:
> Hello Ute,
> >>  There are situations where trees are undesirable because of their
> 'pumping' action.  <<
> I didn't necessarily pick up that the birch's pumping action, and
> consequently lowering the water level of the bogs, is inherently a bad
> thing.  Can you qualify a bit why it's detrimental?

It's a basic question of 'why conserve habitats'. Most of the raised
bogs, e.g. in the Irish Midlands, or in northern Germany have been lost
to exploitation and/or intensifying agricultural practices over
centuries (mostly during the 20th century). With them we have also lost
or are on the verge of loosing the specialised flora and fauna these
peatlands harbour and places of great natural beauty. That's why efforts
are being made to conserve the little that's left and the contribution
these habitats make to biodiversity. In 1992 the European Habitats
Directive has made it encumbent upon EU Member States to place the
remaining raised bogs (and many other habitats) unter legal protection
and to take measures for their maintenance and regeneration where
HABITATS (HAB 96/2 FINAL - EN Version EUR 15)

Degraded raised bogs (still capable of natural regeneration)

"These are raised bogs where there has been disruption (usually
anthropogenic) to the natural hydrology of the peat body, leading to
surface desiccation and/or species change or loss. Vegetation on these
sites usually contains species typical of active raised bog as the main
component, but the relative abundance of individual species is
different. Sites judged to be still capable of natural regeneration will
include those areas where the hydrology can be repaired and where, with
appropriate rehabilitation management, there is a reasonable expectation
of re-establishing vegetation with peat-forming capability within 30
years. Sites unlikely to qualify as SACs are those that consist largely
of bare peat, that are dominated by agricultural grasses or other crops,
or where components of bog vegetation have been eradicated by closed
canopy woodlands."

"Raised bogs can be found in Austria, Belgium, Denmark, Finland, France,
Germany, Italy, Ireland, Netherlands, Spain (Pyrenees and  Cantabrian
mountains), Sweden, United Kingdom."
"There are very few intact or near-intact raised bogs in Europe, except
in Finland and Sweden where active raised bogs are predominant mire
complex type in hemiboreal and southern boreal regions."

If you are interested in peatlands - the Irish Peatland Conservation
Council www.ipcc.org has a nice website.
> >>  The slightly drier conditions resulting from this drainage favor the
> establishment of (typically) birch trees which are opportunists when it
> comes to water supply.  <<
> So before the drains were put in the birch didn't stand a chance, and now
> with the drains in place the birch are moving in?  It sounds like to me that
> if conditions have been created where the birch can grow then they should be
> allowed to do so.  Otherwise, we are trying to maintain a system that no
> longer suits the topography.

see above for (hopefully) an answer to the question 'why?'
> >>  Restoration measures for such peatlands include the removal of the birch
> trees and the blocking of drains.  <<
> If the drains were blocked and original bog conditions restored then birch
> removal seems slightly more appropriate.  However, I bet a lot of trees are
> cleared where the drains are not blocked, and original bog conditions are
> not restored.  Once again we end up pitting ourselves against what nature
> chooses to fill an ecological niche with.

Removing the trees and not restoring the hydrology of the bog does
indeed not make sense. Any restoration programme worth its salt will do
> >>  There are also situations where non-native trees can cause damage, such
> as eucalyptus plantations in arid regions where they compete with native
> vegetation for water.  <<
> I'm not necessarily fond of the eucalyptus tree, myself, as it's way
> overused in international forestry and extremely flammable.  However, just
> about everything on this planet competes for water.  There has got to be
> better grounds for eradicating a species than whether or not it's native and
> requires water to live.

A lot of erosion problems have also been attributed to Eucalyptus
> >>  I guess one has to try and get quite detailed information on the local
> ecology and ecosystems and/or observe natural ecosystems well, before one
> can judge whether certain trees are beneficial or not in a given situation.
> <<
> Well, just label me an extremist, but I'm still not convinced that tree
> removal is the solution for the scenarios you described.  Thanks for
> relating the story, Ute.

I'm not into labelling and equally hope I'm not being labelled. :)
Perhaps the bit of background info explains where I was coming from. The
only point really I was trying to make (using a European example on a
predominantly American list) is that there every situation is different
as there is an endless variety of ecosystems, habitats, and ecological
niches on this planet thriving under endless different combinations of
geology, soils, hydrologies, micro and macro climates. Hence there can
be no *general* rule that says, trees are good or trees are bad, or this
tree is good, that one is not. The study of local ecologies and the
study of phytosociology (why do which plants grow where and in what
combinations) can be very useful tools in developing sustainable
systems, or as in the example I cited, in repairing damage done to
natural systems which have developed over the past 10,000 or so years
and are on the verge of disappearing from this planet - a loss I feel we
cannot afford.
> Kirby


Break the mould - commit random acts of kindness.

Dipl.-Ing. TU Landschafts- und Freiraumplanung
Ute Bohnsack
Sailchearnach, Clogher, Kilfenora, Co. Clare, Ireland
mailto:sustag at eircom.net
Agri-Environmental Consultancy and Translation Services
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