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<Russ Carlson>
posted
In the Lombardy Poplar thread below (http://tree-tech.com/board/?topic=topic5&msg=473) JPS suggested that the loss of a willow tree allowed a hidden spring to emerge.

Do trees really use enough water to keep a hidden or underground spring from rising? Can trees absorb enough to prevent water from puddling on the surface? How much water can a tree absorb/translocate in a day?

I recall way, way, way back in my college days learning that a mature elm might 'drink' in a few hundred gallons a day, during good conditions and if the water is available. If we consider that 1000 square feet of surface with water 1 inch deep has 625 gallons of water, will the tree really use it up very soon (1000 sq. ft. is only a 32-foot circle; rather small for a large tree).

My opinioin is that while trees do use the water and may help reduce the wetness of an area a small amount, they are not sufficient to significantly change the water regime of the soil when it is saturated. Remember too that roots in saturated soil can not respire well, and as a result will not absorb well.

Comments and discussion?
Russ Carlson
 
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<Scott Cullen>
posted
Reply to post by Russ Carlson, on July 26, 2001 at 14:51:44:

Russ, I also recall way, way back anecdotal references to willow trees transpiring well into the hundreds of gallons... maybe even thousands... per day. I imagine if we searched the tree physiology literature we migh find some hard data.

In any case if you think about field conditions... you seldom see trees surviving in standing water (lets exclude riparian species that tolerate seasonal flooding and true swamp trees). What you see is kind of mushy ground. That same 625 gallon volume of water that would create 1 inch of standing water might saturate the soil volume of a much larger circle. And if the water input is say 625 gallons per day and you subtract only a portion of that to evaporation or drainage daily, I suspect an additional 625 gallons per day of transpiration loss could indeed change the moisture content of the soil to a noticeable degree.

That could be compounded if the area you are examining is the low spot and there are a number of trees upslope also intercepting the water that might otherwise make it's way to the low spot.

We've got a project going with some tensiometers in the ground and you really can see the canges in soil moisture. I know of big transplanting projects with scads and scads of tensiometers installed and they irrigate based on the readings. I'd guess equations have been worked out for water usage.

And if you get by all the hype, there seems to be some sound basis for soil moisture loss to tree transpiration resulting in soil shrinkage and resulting structural subsidence on expansive clays.

SC
 
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<Mark Goodwin>
posted
Reply to post by Scott Cullen, on July 26, 2001 at 14:51:44:

This reminds me of a planned condominium development that was defeated by referendum, when it became obvious that the site was clearly in a flood zone.
As part of the project, they had planned to install a local sewage treatment plant, with a drain field covered with Coastal Redwood trees for water absorption.
This was next to a major water course, which incidentally had a 100 year flood incident a few years later. I assume that the planners believed the trees would intercept a lot of water and pollutants.
 
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<Scott>
posted
Reply to post by Mark Goodwin, on July 27, 2001 at 06:13:16:

There seems to be a differeence between absorption/transpiration and "interception."

The latter can slow or trap water for a time, then let it go. It can be a plus... slows down flood flow; or a minus; clogs up flood flow and causes overflow behind. It depends what the system is intended to do. There is actually quite a literature on this.
 
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<JPS>
posted
Reply to post by Mark Goodwin, on July 27, 2001 at 06:13:16:

Even taking into account that any anecdote will grow with time and telling (trees are taller, holes are deeper) I found the story to be credible be cause of personal experiance.

Like the mature honey locust in my folks back yard. When I was a kid water used to stand back there for days, now it is so dry even after rains that we need to water. We've taken down two willows since I was a kid (my mom sais I was never little).

When I waorked for ChemLawn, I removed trees on several properties that had water pooling problems for several years after, may still for all I know . These we silver maple, locust and such.
 
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<Scott>
posted
Reply to post by JPS, on July 27, 2001 at 11:09:54:

Don't forget "fish are bigger."
 
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<JPS>
posted
Reply to post by Scott, on July 27, 2001 at 17:58:20:

I was thinking that they were longer (This big!) when I was posting .

But let us not digress into any other length issues.....
 
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