Have a look at this sage brush:

Like all plants, she gathers most of her water from the top surface of the soil, where it is most quickly lost to the dry air. And yet, she is here, in the hottest, driest part of the landscape.

The how of this is beautiful. All day, she draws water, mostly from the top 30 centimetres of the soil …

… and then, when her roots are dry and the nutrient salts have built up in their tissues, they draw water from deep in the soil, and disperse it to the surface environment …

The images are from Roots Demystified, by Robert Kourik. Have a look: click!

… where it dissolves nutrients and makes water available to surrounding plants, who soak it up at night. The result is a community, building and harvesting nutrients together. Some 35% of the water moves through plants other than the sagebrush (or the tree) that pulled it from the deep soil.

Compare a herbicide-treated apple plantation. Lacking taproots, these trees never leave the surface zone. Not only is any water they have coming from the surface and needing evaporation (and salt-poisoning of soil) to bring it to the surface, but weed-killing has increased the evaporative potential of the soil even further. The 35% of water that is retained by surrounding plant communities is lost. That’s a lot of water.

Compare a natural stream system in the Bella Vista Grasslands. Here (midsummer), the green of the trees does not come from surface water. In effect, the trees are themselves the stream…

… and any water present for the complex communities that accompany them…

… is built up from their night-time hydraulic lifting, and deepened over time.

Green Water, Deepening its Flow, Six Years after Fire

 Because these effects take place on a gravitational slope, the horizontal plane is angled, producing a flow, as the trees and bushes (and yellow clover, above) pass it on from point to point to point, dissipating it laterally every centimetre of the way, even when it leaves…

… for the air.