Xeriscaping: Does returning to desert conditions conserve water? Really?

Xeriscaping in Las Vegas.  Some people in Utah are
adopting this trend which could result in us
have less, rather than more water.

When the Mormons fled the mobs of Missouri and founded a new home in Utah, the valleys were mostly dry desert.  However, if you look over Salt Lake Valley or Utah Valley today, it is a garden of trees, lawn and shrubs.

While I support efforts to conserve water, I am not excited about extreme Xeriscaping (sometimes pronounced Zero-scaping).  Xeriscaping is a practice that makes extensive use of rocks and gravel for ground-cover and uses native plants that require less water.  In theory, plants that use less water should conserve more. Shrubs need less water than trees.  Rocks clearly use less water than grass.  Right? 

When you look over the cities of Utah
trees are the most prominent feature.

So if this were true, we would assume that a rain forest would use up water at enormous rates and suck all of the rivers and groundwater reserves dry in no time.  However, the opposite is true.  Rain forests conserve  water.  They gather water, shade it from the sun, and store it in soil rich in organic matter.  Pour a gallon of water onto the ground at high noon in a rain forest and the spot will still be wet at 7 pm.   Try that in the desert.  Or on a lawn made of rock. It will be dry in 20 minutes.

Salt Lake City has been criticized for not landscaping like they do in desert cities like Las Vegas and others  in "Aridzona".  That's the reason we are not a desert. We have trees and lawns that breath water into the air, tempering the heat, shading the ground, and enriching the soil to allow for storage of more water.

Trees are great store houses of water. So are lawns and shrubs.