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 pump that can extract up to 200 gallons a day from the soil and spew it into the atmosphere. So effective is this ability that David Schneider, in his anti-Gaian 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.

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 which reaches high enough into the sky turns to ice crystals which shade the areas under them, cooling them, causing a regenerative effect. As more of the 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.

What creates this daily pattern? It is orchestrated by the trees. When the light and temperature increase, they start to pump, opening the spiracles on the underside of their leaves, expelling the moisture, which vaporizes and rises high into the air, carried far aloft by the water vapor pressure differential created by the tree's pumping action.

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 most 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 pumps, 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-pumps 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 so efficient in sequestering water that the surplus flows to the sea in great rivers, like the Amazon.

A tall tree is the most effective water pump 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, rather than active pumping. 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 pumping, 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. To some extent deforestation has occured because humans don't like to be rained on every day.

Environments in which the pumping 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.