Merriam's Life Zones are widely used in the Southwest and Mexico. C. Hart Merriam, who headed the U.S. Biological Survey in the late 1800s, noted in Arizona that the major aspects of plant communities changed in a predictable way as one went from the top of San Francisco Peak outside of Flagstaff to the depths of the Grand Canyon. Indeed, the sequence was much like one would see in traveling south from the tundra of northern Canada to the low Southwestern deserts.
On this basis, he erected six altitudinal life zones. At the highest elevations is the Arctic-Alpine Zone, the area above timberline. Descending, one passes through the Hudsonian Zone of dwarfed, gnarled conifers, the Canadian Zone of spruce-fir forest, the Ponderosa-Pine forests of the Transition Zone, the Upper Sonoran Zone grassland and pinyon-juniper woodlands, and the Lower Sonoran Zone of desert. The route from El Paso to Ruidoso carries you from Lower Sonoran to Canadian life zones.
As usual, our mistreated Chihuahuan Desert is ignored in favor of our
neighboring desert to the west.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.