Posted on 07/28/2005 6:17:29 PM PDT by blam
Millions 'wasted' planting trees that reduce water
By Charles Clover, Environment Editor
(Filed: 29/07/2005)
Millions of pounds in overseas aid are wasted every year planting trees in dry countries in the belief that they help attract rainfall and act as storage for water, scientists said yesterday.
In fact, forests usually increase evaporation and help to reduce the amount of water available for human consumption or growing crops, according to a four-year study.
Research on water catchments on three continents says it is "a myth" that trees always increase the availability of water.
Even the cloud forests of tropical Costa Rica had less effect in stripping water out of clouds than previously assumed, according to the study, funded by the Department for International Development.
In one part of a large study, Sampurno Bruijnzeel, of the Free University of Amsterdam and one of the world's leading experts on tropical forests, measured the overall amount of water flowing from wet, forested catchments in Costa Rica and found there was no more water than was flowing from surrounding grassland.
While cloud forests were more effective at stripping water out of clouds, the researchers found that the evaporation was higher than on short vegetation.
The study, for the UK's Tropical Forestry Research Programme, will be controversial as it shows that converting cloud forests to pasture does not cause major reductions in water yields.
In India, South Africa and Tanzania, the study showed that plantation forests actively wasted water and were "ineffective" or "counterproductive" at retaining water.
Studies by Newcastle University in the Indian states of Himachal Pradesh and Madhya Pradesh found that planting trees had a "negative" effect on the supply of water.
The study suggests that efforts to convert agricultural land to forest caused a 16 to 26 per cent reduction in water yield. The study suggests that rainfall evaporates up to twice as fast in forests as it does in treeless areas.
Prof Ian Calder, of Newcastle University, one of the researchers, said: "Putting in more forestry in water-stressed catchments where the water table is 500 ft down and the ground water is being mined for uncontrolled crop irrigation will only aggravate matters."
"The public perception is that where you plant trees, you will be increasing the ground water recharge. The evidence is the opposite," Prof Calder said.
Other "water myths" the study knocks down are that trees, particularly plantation trees, are always beneficial in preventing erosion and stopping floods.
Prof Calder said the study showed that there might be some benefit with plantations taking up water in most years, and reducing annual floods, but in major 1-in-20-year floods, the benefits were "negligible".
Astounding ignorance. Trees make good firewood or wood pulp.
"A suprise to me."
Another thing people are surprised to hear, and still don't believe, is that trees are a source of pollution.
Reagan got bashed and still gets bashed for pointing this out.
But it's true.
Several things come to mind. First, the water run-off from large forests wouldn't be especially great, because the water is held in the undergrowth. While there isn't great run-off, there is a bountiful amount of animal and plant life supported by the water in these eco systems.
On the one hand the study says that trees don't create more rain, but then it also notes that there is greater evaporation from the forests. This makes one wonder if the people running the study understand where rain comes from.
"Some trees", not all trees...
Water attracts trees, not the other way around. Some people just don't think logically.
"Another thing people are surprised to hear, and still don't believe, is that trees are a source of pollution."
I remember a childhood trip to the Smokey mountains where a park ranger explained that the haze in the air was from the trees.
Yup. I remember that. (Reagan's picture still hangs over my desk)
It would seem to me that if there were not enough water.. trees wouldn't grow.
Besides.. this was a FOUR YEAR STUDY? How freepin stupid is that? Four lousy years... don't they know how long trees live? I'm sorry, but I don't care how sophisticated your computer models are, you cannot measure/predict the impact of a forrest on a complex ecosystem in just four years.
The good Lord just doesn't work that way... or that fast.
Really. Which trees don't produce pollen?
Since most trees root systems are on the top 3-6 inches of the ground this study proves that some people get far to much time and gelt to spew their ignorance. In the rain forests of South America, nearly the whole eco system is above ground.
Trees provide the canopy to cool the air by shade and evaporation..causing all that water to go into the air and return as rain..maybe not in that area, but it comes down. The Sahara desert once had forests. After they became extinct the desert was the result.
The biggest polluter on earth is forest fire. Forest fire releases carbon, not only from the fire itself but the ground. And it continues to release that element for years untill a new forest grows. Fire also releases Mercury as well as other elements collected over the years on the ground. So lets get Bruce "The Rabbit" Babbit to get out on another photo op of him with a drip can lighting up a "controlled" burn...the ignorant idiot!
Um, not much survives a 20 year flood. This is overstating the obvious, and ignores the benefit of having trees reduce erosion, which would conserve valuable topsoil.
Some of us learned that in basic Environmental Science merit badge class at summer camp..
He is still lampooned for his comment. He was taken out of context for political reasons and they still run with it.
"Trees provide the canopy to cool the air by shade and evaporation..causing all that water to go into the air and return as rain..maybe not in that area, but it comes down."
Of course, but that wasn't the point of the study.
And water vapor is a greenhouse gas much more powerful than CO2.
I don't consider pollen to be polution. When Reagan addressed this issue, I believe he was refering to some trees which produced a fair amount of oxygen and others which net drains on the oxygen supply.
Millions of allergy sufferers would disagree - as would the kind folks that came up with the term "pollen count", as part of the pollution index.
But everyone is entitled to their opinion, to be sure.
And I couldn't speak to what Reagan was actually referring to - though if he was referring to pollen, he would've been more widely understood, and also correct.
I would suggest that Reagan wasn't talking about pollen. If he had been, he wouldn't have qualified his comments about 'some trees'. He would have said all trees.
As for the pollen count, the inclusion of it in the daily index reporting doesn't make it pollution. It does make it bothersome for people with allergies, which is why they report it.
Thanks for the additional comments.
When Reagan menthioned trees in this manner, he was talking about overall polution in our big cities. (At least I think he was.)
I didn't mean to imply that oxygen was a polutant, but that Reagan's premise was that some trees could compete with humans for the oxygen supply in heavily populated areas.
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