|Title||The temporal dimension of regime shifts: How long can ecosystems operate beyond critical thresholds before transitions become irreversible?|
|Publication Type||Conference Paper|
|Year of Publication||2015|
|Authors||Ratajczak Z, Collins SL, D'Odorico P, Nippert J, Isbell F, Bestelmeyer B|
|Conference Name||100th Annual Meeting of the Ecological Society of America|
|Conference Location||Baltimore, MD|
|ARIS Log Number||319957|
Background/Question/Methods: Ecosystem thresholds are often identified by observing or inducing slow changes in different driver variables and investigating changes in the asymptotic state of the system, such as the response of lakes to nutrient loading or biome responses to climate change. Yet many anthropogenic pressures on ecosystems change rapidly or in discrete steps. Moreover, once an ecosystem crosses a bi-furcation point in the equilibrium states of the system, the transition is often assumed to be irreversible, but such irreversibility is rarely assessed. We tested these assumptions, investigating the temporal dimension of critical thresholds and the reversibility of slowly evolving dynamical systems responding to abrupt changes in external drivers. This study asks if and how long ecosystems can operate beyond a threshold –a bi-furcation point—before they they become trapped in an alternative state. We use two approaches: 1) simulation models; and 2) long-term experiments that pushed semi-arid grasslands and mesic grasslands past critical thresholds and then relaxed these pressures in some plots to test for reversibility.