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  • From: Heide Hermary <heidehermary@pacificcoast.net>
  • To: permaculture@lists.ibiblio.org
  • Subject: Re: [permaculture] "thirsty " trees....
  • Date: Tue, 03 Sep 2002 13:57:40 -0700

I've been following this with some interest as a landscaper, arborist and non-professional forester.

First of all I am wondering who the monkey people are?? This has come up several times in the past. The phrase is wrought with prejudice of some sort, but it's going right over my head.

Secondly I have some observations about trees and water.
Yes, trees evaporate a lot of water, but it also condenses on the tree leaves (most of it being emitted through the stomata on the bottom of the leaf), and much of it is returned to the soil. This water is made available to other life forms that are then able to produce soil that will be able to retain natural precipitation, preventing soil erosion and water runoff.

In addition the shade created by trees prevents the evaporation of water from soil and grass landscapes. We could see this clearly here in Victoria, Canada last year, when we had a total watering ban on lawn areas due to a water shortage: the lawns that were located under trees stayed green, whereas those exposed to full sun went dormant.

Historically the eradication of trees has led to desertification of the land.

I have been surprised to read references from Australia blaming the ABSENCE of trees for RAISED ground water levels, because all other references accredit the PRESENCE of trees with raising the water level. I can't pretend to understand the mechanics of either of these assumptions, at least that's what I believe they are. These contradictions, however, make it clear that there is still little understanding of the relationship between trees, water, climate overall, etc. I would be very careful to blame trees for removing so much water from the landscape that there is not enough for human consumption.
Heide

Mark wrote:

At 07:59 AM 9/3/02 -0500, you wrote:

Hi Mark,

Just dug up some interesting snippets from the Pc design manual...

p.435, "Many [perennial grasslands], in fact are treeless areas established
during periods of icecap retreat, and have never established as forests,
although both soils and climactic factors will permit forest establishment.
Other grasslands are maintained by fire (natural, from lightning strikes; or
managed from human interference) against forest invasion."

p.435, "while a forest may have a visible "standing crop' of 207 t/ha, and
grasses only 7 t/ha, below the ground forests produce 184 t/ha of organic
matter to the 345 t/ha of natural prairie in equivalent soil / climate
regimes (Foth, 1984, based on other studies).


Soil depth in some of these historic grasslands is also phenomenal. Those of you who wonder how industrial ag maintains itself dispite it's madness should look here. 4 meters of prime A horizon lets one abuse the land for generations without paying much penalty. Except dieing of cancer early. I have one of Foth's soil science texts, I'll have to crack it open again....

p. 142, "The composition of the atmosphere is the result of reactive
processes, and forests may be doing about 80% of the work, with the rest due
to oceanic or aquatic exchange."


Hmmm. I thought there was a bigger contribution coming from the oceans. I remember seeing something on fertilizing the ocean with iron to boost the carbon sink effect there and bulk up the sea food production. What will the monkey people think of next ;<)

Lots of room in their to fill in the blanks, but helps to provide some actul
numbers.


Kirby


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Mark P. Ludwig
Poultry Research Lab
University of Wisconsin -Madison
608-262-1730 WK
608-846-7125 HM

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