Tree loss and desertification - a really good explanation

I have always wanted a succinct description on why trees are so critical to the desert and holding and attracting moisture to these vast continental interiors. Found this lovely article the other day.

Some of the highlights:
"To balance the return of fresh water to oceans, ocean water continually evaporates back into the atmosphere to form the clouds that return fresh water to land as rain. However, isotope studies have shown that almost all oceanic moisture falls as rain within the first 150 miles from any coast.

How, then, do life-giving rains manage to reach the vast interiors of continents?

As soon as rain falls to the ground, plants begin to absorb the water into their bodies. However, plants must absorb much more water than needed strictly for metabolic use since plants also lose water through evaporation and transpiration ('evapotranspiration'). Water lost to the air through evapotranspiration by trees is the major mechanism through which air is remoistened as it moves farther inland from oceans.

Among plants, trees are by far the most effective evapo-transpirers. Complementing oceans, trees form the other half of the planet-wide system known as the rain or water cycle. A typical tree breathes out 250 to 400 or more gallons of water per day through the amazingly large surface area of its leaves (an acre of forest can contain well over 1,000 acres of leaf surface area).

It's almost impossible to overstate trees' ability to humidify air and thereby maintain the rain cycle far from oceans. While some rainfall evaporates directly from the ground and from small plants (this can amount to most of a light rain), evapotranspiration by trees accounts for the great majority of inland rain.

Even near oceans, trees are vitally important to re-humidification and rain. When European settlers removed the high forests from the island of Maui, for instance, the once heavily-forested island immediately downwind (Kahoolawe) quickly became a desert island because its source of rain had been the trees on Maui—not the ocean surrounding both islands."

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Why, oh why are humans in drylands so foolish with their water?? (rhetorical question) My dad, a civil engineer by trade (designs water and waste systems), went to a meeting here in Phoenix many years ago to discuss the increasing pressure put on our limited water sources by the rapidly growing population. The public was invited to attend and ask questions. The idea that captured everyone's attention was when some citizen stated that the City should "go out into the desert surrounding Phoenix and cut down all the water sucking trees so that there would be more water for golf courses and swimming pools". My dad tried to explain the water cycle and how we need MORE trees, not less, to enhance our water cycle/table but people were more interested in preserving their immediate rights to create more and more golf courses and have private swimming pools - two things it was proposed that we limit here in the desert.

One thing that did come out of those early discussions was some greywater infrastructure. Now many (possibly all) golf courses in Phoenix are watered by greywater. Hey - it's a definite step in the right direction.

Not to rain on your parade, but those golf courses and swimming pools evaporate a LOT of water. That's why they have to keep pulling the water in from elsewhere. A swimming pool can lose an inch of water on a hot, summer day, and most of what goes on a golf course in the morning comes off in the afternoon. In my years living in the desert, the most humid place was not out on a sand dune, or in a canyon with a stream, or even a date grove, it's the damn golf course. Ask anyone who lives near a golf course if their swamp cooler works well, and then wait for the torrent of verbal abuse about how it won't put out cold air.

But your observation about the desertification of Maui is also pertinent here. Where does all that water coming off the golf courses in Palm Desert and Scottsdale end up? Most likely downwind 50 miles, where the desert has not been colonized by humans -- yet. I wonder if anyone has surveyed the desert vegetation in those areas to see if they have benefited from an increase in precipitation. It would be an interesting study.

John Elliott wrote:Not to rain on your parade, but those golf courses and swimming pools evaporate a LOT of water. That's why they have to keep pulling the water in from elsewhere. A swimming pool can lose an inch of water on a hot, summer day, and most of what goes on a golf course in the morning comes off in the afternoon. In my years living in the desert, the most humid place was not out on a sand dune, or in a canyon with a stream, or even a date grove, it's the damn golf course. Ask anyone who lives near a golf course if their swamp cooler works well, and then wait for the torrent of verbal abuse about how it won't put out cold air.

LOL - good one John! (and you can rain on my parade any time - just let me get my portable water harvesting parade gear on!)

Yeah - the City of Phoenix wanted to ban any more golf courses and limit the permits for private swimming pools - two HUGE water wasters as you pointed out. Pools, in my mind, are especially bad because of all the chemicals you have to keep dumping into them - as you know, chlorine volatilizes in the hot sun.... Although golf courses have abundant chemicals dumped on them too. OY!

You know, I never thought about humidity levels on golf courses and it messing with swamp coolers. And I live practically next door to Encanto Park and golf course. It is NOTICEABLY cooler over there, especially at night. It's not releasing the same heat back to the atmosphere as, say, a parking lot (so at least that's a positive).

But I digress...the point was - WE NEED TREES for so many reasons: as part of the hydrology cycle and to build and clean soil, clean stormwater and clean up air pollution. And for some freakin' shade (what don't folks here get about SHADE?)

Rant over. For now.

Jennifer Wadsworth wrote:

But I digress...the point was - WE NEED TREES for so many reasons: as part of the hydrology cycle and to build and clean soil, clean stormwater and clean up air pollution. And for some freakin' shade (what don't folks here get about SHADE?)

Jennifer, are you aware of the Desert Legume Program at the University of Arizona? This isn't the first, nor the last time I am going to give them a plug. One of the finest seed bank programs for desert plants that I know of. Anyone interested in planting trees in the desert should use them as a resource -- collect seeds and send them in; get seeds from them and raise some seedlings.

John Elliott wrote:Are you aware of the Desert Legume Program at the University of Arizona? This isn't the first, nor the last time I am going to give them a plug. One of the finest seed bank programs for desert plants that I know of. Anyone interested in planting trees in the desert should use them as a resource -- collect seeds and send them in; get seeds from them and raise some seedlings.

I am, and I agree. I've been sifting over their list periodically to see what might work in Phoenix. As you know - Tucson's climate is a little gentler than ours, so I'm looking at the one's that have proven robust in their test fields. And I just really want to get down there and SEE what they have going on. Lately I haven't been able to "get" anywhere due to health issues. But I definitely plan to contact them and see if I can talk to someone and maybe get a tour.

Have you been there?

I just know them by mail order. They are nice about sending out samples. I got half a dozen sample packets of seeds from them and I have started some palo verdes here in Georgia and I keep them on my front porch so they don't get rained on too much.

Wow - Palo Verdes in GA? I wouldn't have thought they'd do well there! But I don't blame you for growing them - they are such pretty trees.

Wow! My home city, Albuquerque, is mentioned in the article about tree loss and evapotranspiration. I can imagine my home town and home state being very different that it is today. Today brown desert fills most of the landscape. Supposedly when the Anasazi were at the height of civilization the land looked very different, trees forests and lots of tiny streams.

I am trying to do my part to restore the landscape although as the article mentioned I would be greatly assisted by other Permies planting trees closer to the ocean to allow the evapotranspiration rains to get closer to me. Thank you Arizona, Mexico and Colorado Permies for the extra trees planted and rain collected on the wind. To the people that would receive the "windfall" of my efforts, your welcome Texas and Oklahoma panhandle.

The article also really hits home on how the Amazon rainforest can turn from rain forest into desert by lack of evapotranspiration.

Brett Andrzejewski wrote:Wow! My home city, Albuquerque, is mentioned in the article about tree loss and evapotranspiration. I can imagine my home town and home state being very different that it is today. Today brown desert fills most of the landscape. Supposedly when the Anasazi were at the height of civilization the land looked very different, trees forests and lots of tiny streams.

I know exactly what you mean. For years I could not imagine what your typical "food forest" might look like in the low desert. Then I read some descriptions of what the Salt River Valley looked like before mass settlement and had an "aha" moment. Our current canal system is based upon models left behind by native peoples.

Brett Andrzejewski wrote:I am trying to do my part to restore the landscape although as the article mentioned I would be greatly assisted by other Permies planting trees closer to the ocean to allow the evapotranspiration rains to get closer to me. Thank you Arizona, Mexico and Colorado Permies for the extra trees planted and rain collected on the wind. To the people that would receive the "windfall" of my efforts, your welcome Texas and Oklahoma panhandle.

Brett - I love the way you think! I have spoken to The Tree People in Los Angeles to see if they would be interested in extending their really great program here - alas, they don't have the resources at this time. I do work with Arizona Community Tree Council and they do great work - The Tree People are just miles ahead of them at this point. So anyway, LA is doing it's part for NV and AZ. AZ will do it's part to pass moisture along to NM and you guys can send some love to TX and OK! Now we're talking.

Brett Andrzejewski wrote:The article also really hits home on how the Amazon rainforest can turn from rain forest into desert by lack of evapotranspiration.

Yeah - that hit me as well. Scary given how easy it is to degrade tropical soils! Best get to planting some trees!

Here's an interesting project: REVEGETATION AND EROSION CONTROL NELSON LAKE PROJECT AREA AT NATIONAL TRAINING CENTER (NTC) FORT IRWIN, CA

I like their water catchments. Looks like something that would be easy to produce in quantity if you wanted to plant large areas of desert.

John - thanks for that link - interesting project indeed! I have to take a better look at it, I've just skimmed it so far. I particularly like that they talk about desert soils, crusts, slowing and redirecting water, etc.

This project reminds me of some other desert restoration projects I've read about, specifically this one in Iran and this one in Mali. There are several more projects in Africa that are really interesting as well. I hope to pull them all into a resource page on my blog, eventually, to keep them in one place. Then there is this project in Saudi Arabia.

Like the article in your post - these are the projects that truly fascinate me. People are dealing with some of the most inhospitable conditions on the planet and they are making headway. It might not be as immediate as projects in other climates, the progress may have many, many setbacks and the successes small in comparison. But to me, these are the most amazing projects ever. They show the scope of human inventiveness and perseverance.

Thanks for adding to my knowledge base!