The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council.

Tuesday, January 29, 2008 - 2:10 PM

Vulnerability and Triggers in Threshold Development: Models from the Chihuahuan Desert

Brandon T. Bestelmeyer, Jeffrey E. Herrick, and Caiti M. Steele. USDA-ARS Jornada Experimental Range, MSC 3JER Box 30003, New Mexico State University, Las Cruces, NM 88003

We review models developed for the Draw and Loamy ecological sites in Major Land Resource Area 42.2 in southwestern New Mexico and review empirical support obtained for parts of the model. We describe evidence for 1) vulnerability to transitions and associated triggers and 2) the characteristics of alternative states. Remote-sensing based evidence supports the notion that fragmentation of grass cover creates vulnerability to transition, and anecdotal evidence supports the notion that high intensity storms serve as triggers that initiate erosion and gully formation. Field measurements indicate that degradation of soil structure, increased run-off, and reduced water infiltration are important feedbacks components driving the transition and reinforcing state changes. These relationships are strongly mediated by soil horizon development differences within the ecological site. The state-and-transition model thus links these scientific studies and provides indicators that can be used by managers to gauge the likelihood of threshold development.

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