PARENT SESSION
Symposium #16: Thresholds and non-linear responses in ecosystems: Understanding, sustaining, and restoring complex rangelands.
Sponsored by ESA Rangeland Ecology Section
Organized by: D.D. Breshears and J. Herrick.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Lecture Hall
Thresholds and non-linear dynamics: an overview .
Archer, Steven1, Lauenroth, William2, Sala, Osvaldo, 1 2
ABSTRACT- Management and restoration approaches have traditionally assumed that change associated with the advent or relaxation of chronic stress or disturbance will be gradual and linear. However, observations are accumulating to suggest that transition thresholds may exist, such that under certain conditions, the probability and rate of change toward new system states may greatly increase. Because of hysteresis effects, systems progressing past these thresholds and into new states may require novel and aggressive management and extended timelines if they are to be restored to their previous configuration. An understanding of the nature of transition thresholds may therefore afford resource managers more opportunities to adjust management and avert undesirable change and better position them to time the implementation of restoration activities and evaluate competing restoration strategies. In this presentation, we will evaluate the role of incremental versus abrupt change and examine the evidence for transition thresholds in contrasting systems. Are there traits that may make systems either vulnerable or resistant to abrupt change? In systems where distinct transition thresholds appear to occur, we will explore the potential for identifying indicators of impending transitions and evaluate how climatic and physical factors might interact with these to trigger change. In cases where systems appear to have been pushed past a transition threshold by chronic disturbance, we will examine the prognosis for reversion to the preceding state following relaxation of the disturbance.
KEY WORDS: change, management, hysteresis, transitions