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  • From: Heide Hermary <heidehermary@pacificcoast.net>
  • To: permaculture@lists.ibiblio.org
  • Subject: Re: [permaculture] "thirsty " trees....
  • Date: Wed, 11 Sep 2002 10:31:32 -0700

At the IFOAM conference just recently one of the speakers mentioned in passing that 90% of the earth's potable water is tied up in living organisms. I don't know where that info comes from, but it goes a long way towards explaining desertification when species are eradicated through pesticides, overgrazing, clearcutting, etc.etc.

As for trees pumping water: not really. A better picture (simplistic, I know) is to visualize the tree as a huge straw, with water literally sucked through it via evaporation through the stomata which are open for photosynthesis. When water supply is low, stomata close, and photosynthesis stops also (C4 plants do this somewhat differently...). Basically what I tried to say before: bare soil will evaporate a huge amount of water. From my observations in this ecosystem here trees actually preserve soil water. I am sure a tall grass prairie will function similarly, but an overgrazed one will act more like an ornamental lawn.

Heide

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?

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.

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.

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.

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.

Kirby

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