6 Geology of Big Bend National Park: What Have We Learned Since Maxwell and Others, 1967?

Thursday, 11 April 2002
1:30 PM - 5:30 PM

GRASSLANDS TO BADLANDS? RECENT LANDSCAPE CHANGES IN BIG BEND NATIONAL PARK

Paper number: 6-12
Program: SYMPOSIA SESSIONS
Time: 4:40 PM – 5:00 PM

Authors

Abstract

Endless miles of grassland greeted the early settlers in the area that was to become Big Bend National Park. A century later, the large expanses of native grasslands are gone. Here and there, patches of grass maintain a tenuous hold in miles of creosote bush and other desert scrub. A visitor entering the park through Persimmon Gap today sees little evidence of what once was. Crossing the long open stretch of the Tornillo Flats, it is hard to believe that this broad valley once held verdant grasslands that grew "knee-deep to a horse" and were harvested as hay for livestock. Once, herds of pronghorn raced across these flats, desert bighorn sheep entered the valley to visit springs, and Mexican gray wolves worked the area in search of prey. Now, all are gone. What happened to cause such a dramatic change? More importantly, can the grassland be restored, or is the area destined to become a landscape of anthropogenic badlands?

A recent assessment in the northern portion of the park found over 100 water diversions and almost that many stock ponds left over from the ranching days. These structures, in addition to loss of grass cover from overgrazing have altered increased overland flow and concentrated runoff, resulting in almost 1000 acres of gully systems, which are gradually eroding into the few remaining patches of native grasslands. Large expanses of bare soil are increasing due to dying creosote. Until recently the creosote was thought to be declining due to decreased infiltration resulting from the loss of the grass cover. However, new information indicates that nitrogen levels in the soil may be increasing beyond the tolerance of desert vegetation. Biological soil crusts appear to stabilize the soil and provide microhabitats for seed germination, however the high nitrogen levels may also be affecting these organisms.