Often it's hard to untangle the effects that man has on the environment from natural changes. This has been prominent in the news in recent years in arguments over the causes of global warming—natural or man-made? This phenomenon seems increasingly clear to be at least in part the effects of human activity. Some past events, however, likely will never be sorted out.
In the mid to late 1800s, the Southwest underwent a cycle of arroyo
cutting. Streams and ephemeral drainage ways barely incised into the surface of the
ground began to excavate deep arroyos, sometimes to 20 or more feet. In consequence,
groundwater levels fell, and grassy valleys turned into shrub deserts. Natural or
manmade? Arguments run the gamut from drought alone to overgrazing by cattle to some
combination of the two. Likewise, extensive grasslands of the northern Chihuahuan
Desert were replaced in large part by desert scrub even where arroyo cutting was
absent. Coinciding with both drought and the introduction of huge numbers of cattle,
once again we likely will never know where the blame lies.
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.