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Peer Review Draft Synthesis and Assessment Product 4.2 Thresholds 1 Peer Review Draft 2 Synthesis and Assessment Product 4.2 3 Thresholds of Change in Ecosystems 4 Authors: Daniel B. Fagre (lead author), Colleen W. Charles, Craig 5 D. Allen, Charles Birkeland, F. Stuart Chapin, III, Peter M. 6 Groffman, Glenn R. Guntenspergen, Alan K. Knapp, A. David 7 McGuire, Patrick J. Mulholland, Debra P.C. Peters, Daniel D. 8 Roby, and George Sugihara 9 Contributing authors: Brandon T. Bestelmeyer, Julio L. 10 Betancourt, Jeffrey E. Herrick, and Douglas S. Kenney 11 U.S. Climate Change Science Program 12 Draft 5.0 SAP 4.2 9/26/2008 1 1 Table of Contents 2 Executive Summary............................................................................................................ 5 3 Introduction................................................................................................................... 5 4 Definitions.....................................................................................................................5 5 Development of Threshold Concepts............................................................................ 6 6 Principles of Thresholds ............................................................................................... 7 7 Case Studies.................................................................................................................. 8 8 Potential Management Responses............................................................................... 10 9 Recommendations....................................................................................................... 12 10 Chapter 1—Introduction and Background........................................................................ 14 11 1.1 A Sudden Change in Ecological Systems............................................................. 14 12 1.2 The Response of the Climate Change Community............................................... 16 13 1.3 The Goal of SAP 4.2............................................................................................. 19 14 Chapter 2—Ecological Thresholds................................................................................... 22 15 2.1 Introduction........................................................................................................... 22 16 2.2 Early Development ............................................................................................... 23 17 2.3 Current Discussion of Threshold Phenomena....................................................... 26 18 2.4 Ecological Thresholds Defined for SAP 4.2......................................................... 29 19 2.5 Factors that Influence Persistence, Resilience, and Robustness.......................... 31 20 2.6 The Bottom Line.................................................................................................. 33 21 Chapter 3—Case Studies .................................................................................................. 36 22 Case Study 1. Ecological Thresholds in Alaska ......................................................... 36 Draft 5.0 SAP 4.2 9/26/2008 2 1 Case Study 2. The Mid-Continent Prairie Pothole Region: Threshold Responses to 2 Climate Change............................................................................................... 49 3 Case Study 3. Massive Forest Die-Back as a Response to Climate Change .............. 55 4 Case Study 4. Thresholds in Climate Change for Coral-Reef Ecosystem 5 Functioning ..................................................................................................... 65 6 Chapter 4—Examples of Threshold Change in Ecosystems ............................................ 75 7 4.1 Background........................................................................................................... 75 8 4.2 Evidence of Thresholds from the Past .................................................................. 75 9 4.3 Evidence of Sensitivity to Current Stressors ........................................................ 77 10 4.3.1 Temperature Increase................................................................................... 77 11 4.3.2 Moisture Availability................................................................................... 79 12 4.3.3 Climate Interactions..................................................................................... 79 13 4.3.4 Climatic Variability Increases...................................................................... 80 14 4.3.5 Multiple Stressors and Climate Change....................................................... 81 15 4.3.6 Disturbance Regimes and Climate Change.................................................. 86 16 Chapter 5—What Can Be Done?...................................................................................... 89 17 5.1 Integration of Management and Research ............................................................ 89 18 5.1.1 Need for Conceptual Models ...................................................................... 89 19 5.1.2 Scaling.......................................................................................................... 90 20 5.1.3 Apply Models from Other Disciplines......................................................... 93 21 5.2 Adaptive Management.......................................................................................... 94 22 5.2.1 Role of Monitoring . .................................................................................... 95 23 5.2.2 Role of Experiments .................................................................................... 97 Draft 5.0 SAP 4.2 9/26/2008 3 1 5.3 Management by Coping........................................................................................ 99 2 5.3.1 Reducing Multiple Stressors........................................................................ 99 3 5.3.2 Triage ......................................................................................................... 100 4 5.3.3 System-Level Planning and Policy ............................................................ 101 5 5.3.4 Capacity Building and Awareness............................................................. 102 6 5.4 Summary............................................................................................................. 103 7 Chapter 6—Summary and Recommendations................................................................ 105 8 Summary................................................................................................................... 105 9 Recommendations..................................................................................................... 105 10 Before ...................................................................................................................... 106 11 During ...................................................................................................................... 107 12 After ...................................................................................................................... 109 13 References Cited ............................................................................................................. 111 14 Appendix A—Glossary................................................................................................... 152 15 Draft 5.0 SAP 4.2 9/26/2008 4 1 Executive Summary 2 Introduction 3 In the past three decades, climate change has become a pronounced driver of 4 ecosystem change. Changes in phenology, range shifts of species, and increases in 5 disturbances such as wildland fires have all reflected ecosystem scale responses to a 6 warming biosphere. There have also been abrupt, nonlinear changes in ecosystems where 7 the levels of response to incremental increases in global temperature have suddenly 8 changed trajectories. These thresholds of ecological change are not well understood but 9 are potentially critical to adaptation strategies for managing natural resources in a rapidly 10 changing world. Sudden, unanticipated shifts in ecosystem dynamics make planning and 11 preparation by managers intensely difficult. One of the primary goals of the ecosystems 12 research element and of goal 4 of the Climate Change Science Program (CCSP) is to 13 enhance the understanding and ability to predict and forecast effects of climate change on 14 ecosystems. This synthesis is intended to evaluate the current state of understanding of 15 thresholds and recommend possible actions to improve knowledge and adjust 16 management priorities even with incomplete understanding of what drives thresholds of 17 change and when they will occur. The focus is on North American ecosystem threshold 18 changes and what they mean for human society. 19 Definitions 20 This report defines an ecological threshold as the point where there is an abrupt 21 change in an ecosystem quality, property, or phenomenon or where small changes in an 22 environmental driver produce large, persistent responses in an ecosystem, which is not 23 likely to return to the previous more stable state. Fundamental to this definition is the idea Draft 5.0 SAP 4.2 9/26/2008 5 1 that positive feedbacks or instabilities drive the domino-like propagation of change that is 2 therefore potentially irreversible. 3 “Systemic” risk or risk that affects the whole organism (ecosystem or economic 4 system), not just isolated parts, provides a useful example. It corresponds to widespread 5 coordinated system failure characterized by a catastrophic change in the
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