The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008 - 9:10 AM
Current Status of the State-and-Transition Framework
Tamzen Stringham, Rangeland Ecology and Management, Oregon State University, Strand Ag Hall 202, Corvallis, OR 97333, David D. Briske, Department of Ecosystem Science and Management, Texas A&M University, 2138 TAMU, College Station, TX 77843, Brandon T. Bestelmeyer, USDA-ARS Jornada Experimental Range, MSC 3JER Box 30003, New Mexico State University, Las Cruces, NM 88003, and Pat L. Shaver, West National Technology Support Center, USDA-NRCS, 1201 NE Lloyd Blvd. Suite 100, Portland, OR 97232.
State-and-transition models (STM) have been widely adopted as a tool for explaining plant community dynamics and response to disturbance within rangeland ecosystems. Our understanding of the STM concepts has advanced substantially since they were introduced by Westoby et al. (1989) and modified by Stringham et al. (2003). This paper summarizes recent advancements in STM concepts presented at a State-and-Transition workshop sponsored by Oregon State University and NRCS, August 2006. The STM framework is founded upon the concept of ecological resilience, however models to-date have focused primarily on ecological thresholds with little acknowledgement of the triggers and feedback mechanisms associated with a reduction in ecological resilience and a subsequent potential threshold event. Ecological resilience describes the amount of change required to transform a stable ecosystem, maintained by one set of reinforcing processes and structures, to an alternative stable state defined by a different set of processes and structures. Effective STM’s must focus management attention on maintenance of ecological resilience to prevent stable states from exceeding thresholds. Resilience management changes the focus from threshold identification to within-state dynamics that influence resilience and decreases vulnerability to thresholds. Attention to within-state dynamics emphasizes the need to identify community phases that are at-risk of a threshold occurrence. Once a threshold has been crossed identification of the feedback mechanisms supporting the alternative stable state allows management to develop restoration practices specifically designed to recover the ecological processes that supported the pre-threshold state. Migration of alternative stable states back across thresholds in response to management prescriptions may be best defined as restoration pathways. Restoration pathways convey that restoration practices are required to reestablish the former state. We recommend that the STM framework incorporate triggers, at-risk communities, feedback mechanisms, and restoration pathways and develop process-specific indicators that enable managers to identify at-risk plant communities and potential restoration pathways.