Greening the Desert

Granted, the desert has its own beauty, and as an inhospitable environment, it provides shelter to life that has lost habitat to human encroachment elsewhere. But the contributors to this web-published document take it as given that forests are better. So this is about turning desert into forest.

What is a desert?

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The single most definitive factor of a desert is a lack of water circulating in the environment. To prevent desertification, this water must be in a form immediately available to beings living there; not in a deep subsurface aquifer, hoarded by one particular specie, thermally or chemically bound, or in clouds floating overhead. Water is circulated in a bios to a much greater level than it is actually consumed. For our present purposes, we will consider the water taken out of the environment via photosynthesis to be negligible, because it is balanced by the water liberated when carbohydrates, fats and proteins are metabolized. The more the gift of water freely moves in an environment, the less chance a desert has of taking hold.

A strict definition of a desert does not need to concern us here. There is so much land on this planet that could use more water, but the planet as a whole does not lack water. Our real concern needs to be how we can keep more water in the environments that lack it.

Fresh water in retreat worldwide

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...is arguably one of the world's spectacular failures of land management.

The photo above shows the ravaged land of Anza Borrego, California, where violent flash floods periodically scour every vestige of life off the slopes of jagged canyons.

Most of the destruction happened on our watch (that is, when humans were pretty much in control of what was going down on the terrasphere), and is still continuing, impressively, today. As an example, the ends of this modern culvert shown at right, passing the water that periodically washes down Cathedral Canyon, AZ (36.8373° N 111.6267° W), now hang precariously at least 5 feet above the floor of the wash in which it was installed.

The aridity of this region is not due to a lack of water, however. Clouds, like these shown over Organ Pipe National Monument in southern Arizona, abound over the American desert, and frequently release their water. Often in the afternoon the horizon is dotted with slanted streaks of precipitation falling from clouds. Not much of it ever reaches the ground, however. Each raindrop, falling thru the desert's heat and aridity, evaporates away in its 6,000 foot descent to the desert floor. So the clouds, their water returning to them, continue their eastward drift and find more suitable beneficiaries of their bounty.

Reconstruction of the North American desert has to begin with preventing washes, arroyos and canyons from eroding further. Highly adapted to the dry soil and rainfall patterns, the native flora have shallow root patterns useful in absorbing moisture from light, brief rains, and are incapable of stopping gullying.

The mighty saguaro cactus, shallow-rooted, is no match for a flash flood

Neither is the ocotillo

Australia is the driest continent, and has one of the most variable rainfall climates in the world. The 2006 season brought a drought that was the worst on record. Rampant fires devastate agricultural areas, rivers drying up, crops failing (the wheat crop slashed 64% and may be forced to import grain in 2007), and farmers forced to sell off their livestock. The government has pledged financial aid for despairing farmers, already laden with debt after five straight years of drought. Some earned no income at all in 2006. A book, Drought in Australia explores the causes, impacts and history of drought in Australia; how drought is defined and measured; climate change in relation to changed rainfall conditions; water use; drought assistance measures; and practical ways in which farmers and their families can plan for the extreme impacts of future droughts.

Europe

Europe is currently experiencing a dry spell. The foto above shows the bare riverbed at les Ponts de Cé, France, completely devoid of water in September, 2005. Victim of a combination of excessive domestic water use, agricultural diversion, too few trees, and probable atmospheric disruption due to global warming, the Loire is lower now than in anyone's recent memory.

Are all deserts man-made?

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Photo of Baalbek courtesy Risto Aikonen

Clearly, some are. The Syrian desert, stretching from Lebanon in the west to the Persian Gulf in the east, once contained the "Fertile Crescent", and the cedar forests of Lebanon were cut down to build many ships, temples and markets. Human activity, both in exceeding the carrying capacity of the land and in protecting goats from predation, stripped the land of its greenery. The human cultures that wasted this land may have originated in North Africa, then spread thru Egypt, Mesopotamia, Phoenicia and up to Greece and Italy. Deserts exist primarily in the horse latitudes, where you might expect the temperate climate to be more hospitable to life than at the equator.

On the other hand, some of our great deserts, such as the Mojave in the United States and the Gobi in central Asia, may simply be too far from a source of rain derived from evaporated seawater to be anything but a desert.

So the real truth is probably somewhere in between these extremes. The only thing we can change is human activity, so here we explore those human behaviors (and the cultures that spawn them) tending to cause or prevent deserts. We will search for past human habitation of all our deserts, and study them to see what relation they may have had to the earth changes that occurred there. We will take a hard look at the balance between proactively working to improve a natural environment and letting nature take its course.

An excellent resource on the influence of humanity on soils over time is W.C. Lowdermilk's Conquest of the Land through Seven Thousand Years (1939).

What human behaviors create deserts?

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We will explore all the things people do to turn a fertile environment abundant in water into a desert. They include:

• Agriculture
  • Slash and burn - Please, folks, can we stop the burning? If you need to burn wood to cook or stay warm, or even having a beer around a bonfire, that's just what you have to do. But if you are clearing land or even doing yardwork around your suburban home, why not just pile the wood or leaves instead of burning it? It is easy enough with a lopper and a bowsaw to compact the pile. While it is decomposing, it holds moisture, shades soil, affords a microenvironment to aid biodiversity, prevents the carbon from turning into CO₂ (a major contributant to the greenhouse effect in the atmosphere), and later will yield a source of topsoil.

    Afraid of the snakes that may come to live in the pile? Why not take the time to learn to identify snakes? So very few of them are actually hazardous to humans; I would rather have a snake in my house than a rat any day! Snakes don't raid your larder and don't have fleas, but they DO eat rats.

  • Irrigation, and the dams created so that irrigation becomes possible over large areas, may be one of the least sustainable of human practices. Irrigation, especially if done with water from deep-lying and highly mineralized fossil aquifers, can lead to salinization of the soil that takes millenia to reverse. An excellent book on the mis-management of North American water resources is Marc Reisner's Cadillac Desert
  • Tillage - Healthy soil contains many micro (and not so micro) organisms, all living together in a complex ecological interaction that we are only now beginning to understand. With little exception, these organisms need moisture, shade (direct sun will kill them), a source of decaying organic material free of toxins to use as nutrients, minerals and a moderate temperature. One of the most important soil-building functions of these entities is the release of acids and other substances that break down the non-organic components of soil and allow them to release life-supporting minerals. Tillage, by exposing soil to the direct sun and wind, interferes with soil formation. It allows the soil, over time, to dry out and lose its organic content.
• Clearcutting
• Paving / Runoff
• Trampling
• Water hording / Water diversion / Aquifer Pumpdown

What cultures underly these behaviors?

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As a gross simplification, it might be useful to list attributes of two opposing world views of how we relate to the environment. Since these are caricatures, we need to realize that we all have aspects of these within each of us, but these polar opposites let us see where we fit in this spectrum. For lack of better terms, let's call them GAIAn and GOBian (Good Ole Boy-ian) culture. Further, we will assume for now that Gaian culture promotes forests, and GOBian culture promotes deserts.

OK, so we have had a little fun with this. There are of course, complications to this simplistic mapping of human culture. But the issue of culture and world view is very central to our ability to green the desert: it is as much a task of social engineering as a technical one.

Nature Abhors a Vacuum

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Life on this planet is advanced enough to take advantage of any vacancy in an ecological niche. If disturbance in an ecosphere displaces or removes some of the species living in it, other organisms move or adapt so they can fill the same role. Since we have disturbed many part of the biota in which we operate, not only by destroying native organisms, but by introducing foreign ones, it should not be surprising that an invasion of non-natives can have dramatic effects.

In a desert, especially, where the ratio of biomass and its concomitant regulation of bios variables to the rest of the environment is low, non-native exotics can sometimes take a firm foothold. If these species are adapted to particularly inhospitable environments, they are known as "pioneer species", because they are Nature's footsoldiers. You can learn about individual ones in a Pioneer species database. They take a tentative foothold in a hostile environment, and start the process of building soil, water and thermal regulation.

However, nature abhors monoculture almost as much as she does a vacuum, so monocultures of pioneer species eventually give way to a healthy environment filled with a stable mix of organisms, which is called a climax environment.

Pioneer Species

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Pioneer species are characterised by a high tolerance to environmental extremes in such parameters as heat, salinity, humidity, predation and pH. They are very scrappy individuals. Generally, pioneer organisms are not good to eat, being defended by thorns, dry or tough tissue, toxic compounds internally or as exudates. They are usually very fecund. Frequently they modify their environment to make it less hospitable to competitors, but more often they create an environment that welcomes in a more complex or higher order ecosystem and then bow out, to continue their tasks elsewhere.

Over a timescale often too long for us to appreciate, they make an environment more hospitable to life. Plants and animals work together to build soil where only sand and rock once existed. Often, just as a cancer operation on a person is not a pretty picture, the colonization of an environment by pioneer species looks like the cure is no better than the disease.

We have to look very critically at condemnations of pioneer species by people who are in positions of authority. Somtimes an anthropomorphic agenda blatantly shines thru the rhetoric. One group may condemn an infestation of pioneer trees because they have encroached on a golf course, or an animal has displaced or predated a favorite game foul. More frequently, the complaints are more genuine. Claims that a pioneer has caused topsoil or water loss, wind pattern shifts, or biodiversity decline need to be given careful consideration.

The way we relate to the organisms in an environment can be likened to the way we wage war on fellow humans. We have weapons of mass destruction; every day we unleash millions of unspeakable, shameful cruelties on the other occumpants of the planet. In electing ourselves mediators in the battle for environmental healing, we need to fully understand the process of succession (the process by which pioneer species in a environment are replaced by climax individuals) before we bring out the chainsaws.

In the photo above, a Tamarisk, Tamarix chinensis, a pioneer specie, has been shattered by the onslaught of gravel during a flash flood in the Panamint Valley's Happy Canyon. But the Tamarisk's root system held firm, and new growth indicates the story is not yet finished. By stabilizing the droppings of another alien lifeform that populates the canyon, ferile burros, they appear to have a chance at establishing a soil bed in one of California's most austere riparian environments, the canyon floor.

I now believe that Tamarisk is a critical ally in reclaiming deserts, because the main focus generally is preventing erosion, and specifically, the erosion needs to be stopped in the locus of the flash flood, because that is where the real damage occurs. Tamarisk is the only thing I have seen in the desert capable of doing that job, and it does so superbly.

The bottom line is this: Tamarisk builds soil in the canyon bottoms like nothing else can. The photo above shows large tree trunks (arrows), washed into the canyon by a flash flood, that have been caught by a stand of young Tamarisk. Because the stands of Tamarisk are so matted, it can also stop soil, gravel and boulders.

Aside from building soil, Tamarisk also does other things. It provides almost total shade in which many types of animals take shelter from the desert sun. On my last trip thru the desert, in June 2005, the tamarisks were in flower, and I did not have the time to begin to count the number of different pollinators that were exploiting the blooms; the treetops were alive with a roaring hum of insects. I also found a three inch mushroom cap under one of the trees. It is not likely that it was dropped there by an errant tourist; so I suspect it may be a concomitant species. Much more study is needed!

There is no shortage, however, of calls on the Web for volunteers to help eradicate the Tamarisk, and the burros are being eliminated by a shooting program from the next valley to the east, Death Valley.

Interestingly, attempts to control the Tamarisk can lead to a real mess. The tree responds to fire or cutting by sending up a nightmarish thicket of thorny suckers. If the trees were managed by pruning lower branches, they can form a shade canopy that would be pleasant for hikers while it was building topsoil. Because Tamarisks so completely dominate an environment, taking them all out results in a soil that will be quickly washed away unless reseeded with something else. What that 'something else' is, is anybody's guess.

Generally, the French have more of a laissez-faire attitude than USAns. Properly pruned, a line of Tamarisk cultivars in the foto above is developing straight, strong trunks and over time will provide a luxuriant shade canopy for vacationers on the Ile de Ré in Bretagne.

What happens in a Rainforest

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The Amazon courtesy the BBC

First, let's look at what happens in the antithesis of a desert, the rainforest.

On a typical day in a rainforest the sun rises in the east and begins to fill all of creation with its waxing light. The new day is crisp and the air is drier than at any other time of day. The day becomes hotter and all the creatures take solace in the shade of the broad leaves which prevent all but a minute portion of the sun's ferocity from reaching the forest floor. But in the early afternoon something else blocks the sun's intensity: the light in the forest dims as wispy clouds intercede. Water vapor reaches high into the sky and condenses. These shade the areas under them, cooling them, causing a regenerative effect. As more vapor condenses, it provides more shade which in turn causes more condensation. Finally, a drenching downpour ensues, again inducing the creatures to seek shelter under the broad leaves. Dusk falls and the clouds, depleted, reduce their patter to a drip. The coolness of night squeezes the remaining moisture out of the air, and the moon may shine thru the mists created by the falling dew.

The Water Battery

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Trees shade us, feed us, make our most prevalent building material out of sunlight, air and water, limit winds, attract lightning away from our abodes, mulch our gardens, heat our houses and perform a myriad of other functions.

One of their most important contributions, however, is one very few people ponder or have even heard about: a tree is a wick that can extract up to 200 gallons a day from the soil and spew it into the atmosphere.

What creates this daily pattern? It is orchestrated by the trees. When the light and temperature increase, they open their stomates, expelling the moisture which vaporizes and rises high into the air, carried far aloft by the water vapor pressure differential created by the humidity gradient.

In the orchestral pit of this hydrodynamic symphony, the soil, water from the previous day's downpour slowly percolates into the water table, down to the creeks which feed rivers. But on its way, root hairs absorb some of it, and divert it skyward. The input of this system is ultimately derived from oceanic evaporation, and its output eventually feeds into the sea. The difference between these two flows is the water stored in the system for use by terrestrial life. The more effective the trees are as wicks, the more water they can sequester in the air, and prevent from flowing out of the system via the rivers. In a forested area a thousand miles wide, a mean windspeed of 5 miles per hour will carry any one water molecule only 40 miles in any 8 hour period, which means that the potential loss, worst case, from 'throwing away' water is only 4%, whereas the loss from NOT throwing it away would be total. Thus, zen-like, the forest keeps its water by giving it away. A clearer case of absolute altruism cannot be found, one that works only if it is performed in the security engendered by absolute community of being. It is an act of always falling, of juggling. Three balls are in the air at all times.

As Schneider points out, a small patch of such efficient tree-wicks can be devastating to a local ecos, drawing down the water table, because it serves as a point dissipator; that is, the gradient lines of hydration fan out radially. A large expanse of them, however, comprise a summation of many such points and the loss of any one is made up by contributions from all the others so that net loss approaches zero. It is very efficient in sequestering water because even though the density of water the atmosphere can hold is low, the sheer depth of the atmosphere is much greater than that of the topsoil.

A tall tree is the most effective water wick by virtue of its massive surface, sending skyward in the best case many times the contribution a grass can make, especially one cropped to half an inch by livestock. In fact, much of the contribution to daytime water evaporation of a lawn is from passive heating of the soil by the sun, due to its low surface area and the high soil temperature. This type of passive evaporation is damaging to soil organisms because the soil temperature is unregulated due to the lack of shade. Eventually, the soil dies.

In an environment supporting maximum wicking, the water cycles from the soil to the air daily. It simply rains every afternoon, and every morning is clear and bright. This is an environment in which Gaia is in maximum control. Mostly, deforestation has occurred by the human desire to raise grazing animals to provide meat, but to some extent deforestation has occured because people don't like a lot of rain.

Environments in which the wicking has been compromised lose the daily characteristic of the water cycle; as more and more of the trees are cut out, the cycle lengthens and becomes more erratic because, being more weakly influenced by the trees, it becomes more influenced by outside forces, other weather summations. Chaos becomes more evident in the weather pattern. My own area, in the mountains of southwestern Virginia, experiences a rough 6 day pattern, two days of rain and four of clear. Because it is more erratic than the rainforest, the influence of the vegetation is decoupled, at least in peoples minds, from the vicissitudes of weather. In areas where there are no trees, the water cycle streches out to weeks, and months. In the worst case it becomes annual, and becomes ENTIRELY dependent on weather patterns originating outside the area.

If we want to be free of erratic weather; have abundant supplies of fresh unchlorinated water, live without air conditioning and have our houses cease being robbed of their heat in winter by raging wind, we have no choice but to reforest.

So effective is this wicking ability in some pioneer species that David Schneider, in his article Slow Motion Explosion: The Exponential Spread of Exotic Species, [Whole Earth Review, 83:101] condemned the Eurasian Tamarisk:

Plants that drink a lot of water -- like the ...tamarisk, which absorbs about 200 gallons per day -- can seriously draw down the water table, eliminating ponds and streams, as well as the insects and animals that depend upon them.

Insects ARE animals, and Schneider is ignoring the obvious consequence that any tree 'drinking' that much water daily would explode. He is criticising a function common and important to Gaia that all trees perform to varying degrees: the creation of rain.

Success Stories from...

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Australia
Africa: the work of Wangari Maathai
     Ethiopia
     Tanzania
India
Jordan
Urban areas