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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #345461
Title: The interactive effects of press/pulse intensity and duration on regime shifts at multiple scales

Author
item RATAJCZAK, ZAK - University Of Virginia
item D'ODORICO, PAOLO - University Of Virginia
item COLLINS, SCOTT - University Of New Mexico
item Bestelmeyer, Brandon
item ISBELL, FOREST - University Of Minnesota
item NIPPERT, JESSE - Kansas State University

Submitted to: Ecological Monographs
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2016
Publication Date: 5/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5699154
Citation: Ratajczak, Z., D'Odorico, P., Collins, S.L., Bestelmeyer, B.T., Isbell, F., Nippert, J.B. 2017. The interactive effects of press/pulse intensity and duration on regime shifts at multiple scales. Ecological Monographs. 87:198-218. https://doi.org/10.1002/ecm.1249.
DOI: https://doi.org/10.1002/ecm.1249

Interpretive Summary: Regime shifts are difficult-to-reverse transitions in ecosystems. Regime shifts are predicted to occur when the intensity of some driver variable, such as temperature, annual harvest rate, or nutrient addition rate, gradually approaches and crosses a threshold value, initiating a transition to an alternative state. However, many driver variables now change rapidly as presses or pulses, not gradually, requiring new conceptual frameworks for understanding and predicting regime shifts. We argue that identifying and controlling regime shifts in response to presses and pulses will require a greater focus on the duration, not just the intensity, of changes in driver variables. We present multiple lines of evidence to suggest that the occurrence of regime shifts depends on both the intensity and duration of changing driver variables.

Technical Abstract: Regime shifts are difficult-to-reverse transitions that occur when an ecosystem reorganizes around a new set of self-reinforcing feedbacks. Regime shifts are predicted to occur when the intensity of some exogenous driver variable, such as temperature, annual harvest rate, or nutrient addition rate, gradually approaches and crosses a threshold value, initiating a transition to an alternative state. However, many driver variables now change rapidly as presses or pulses, not gradually, requiring new conceptual frameworks for understanding and predicting regime shifts. We argue that identifying and controlling regime shifts in response to presses and pulses will require a greater focus on the duration, not just the intensity, of changes in driver variables. In ecosystems with slower dynamics, transitions to an alternative state can take years to decades and as a result, a driver press with an intensity capable of resulting in a regime shift over long time spans may fail to cause a regime shift when applied for shorter durations. We illustrate these ideas using simulations of local-scale alternative stable state models and preliminary evidence from long-term grazing and eutrophication experiments. The simulations also suggest that small changes in the duration of driver presses or pulses can determine whether an ecosystem recovers to its original state. These insights may extend to larger scales. In spatially extended simulations that included patchiness, spatial heterogeneity, and spatial connectivity, all patches recovered to their original state after shorter presses. However, once press duration exceeded a threshold, growing proportions of the landscape shifted to an alternative state as press duration increased. We observed similar patchy transitions in a catchment-scale experiment that reinstated frequent fires approximately halfway through a regime shift from grassland to shrubland, initiated by fire suppression. In both the local- and larger-scale models, the threshold duration needed to elicit regime shifts decreased as press intensity increased or when factors counteracting regime shifts weakened. These multiple lines of evidence suggest that conceptualizing regime shifts as an interactive function of the intensity and duration of driver changes will increase understanding of the varying effects of driver presses, pulses, and cycles on ecosystem dynamics.