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The Structure and Functioning of Dryland Ecosystems

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The Structure and Functioning of Dryland Ecosystems Prepared in cooperation with the National Park Service The Structure and Functioning of Dryland Ecosystems— Miller— Conceptual Models to Inform Long-Term Structure and Functioning of Dryland Ecosystems Dryland of Functioning and Structure Ecological Monitoring —Scientific Investigations Report 2005-5197 Report Investigations —Scientific Scientific Investigations Report 2005–5197 U.S. Department of the Interior Printed on recycled paper U.S. Geological Survey Front cover 8-1/2" 11" Back cover 8-1/2" 11" The Structure and Functioning of Dryland Ecosystems—Conceptual Models to Inform Long-Term Ecological Monitoring By Mark E. Miller Prepared in cooperation with the National Park Service Scientific Investigations Report 2005-5197 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior Gale A. Norton, Secretary U.S. Geological Survey P. Patrick Leahy, Acting Director U.S. Geological Survey, Reston, Virginia: 2005 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS–the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Miller, M.E., 2005, The Structure and Functioning of Dryland Ecosystems—Conceptual Models to Inform Long-Term Ecological Monitoring: U.S. Geological Survey Scientific Investigations Report 2005-5197, 73 p. Keywords: arid ecosystems, conceptual model, degradation, disturbance, ecosystem dynamics, ecosystem manage- ment, ecosystem structure and function, indicators, monitoring, resilience, resistance, stressors. iii Contents Abstract ...........................................................................................................................................................1 Acknowledgments .........................................................................................................................................1 Introduction and Background ......................................................................................................................1 Purpose and Content of This Report ..................................................................................................1 Vital Signs Definition ............................................................................................................................4 Purposes of Conceptual Models ........................................................................................................4 Geographical and Ecological Scope .................................................................................................4 Structure and Functional Relationships .....................................................................................................5 Background: The Jenny-Chapin Model of Ecosystem Sustainability ..........................................5 General Model .......................................................................................................................................7 Regional Climatic and Atmospheric Conditions .....................................................................7 Precipitation Regime ..........................................................................................................7 Wind ....................................................................................................................................15 Soil Resources............................................................................................................................15 Inherent Edaphic Heterogeneity ....................................................................................15 Soil Functions and Soil Quality .......................................................................................15 Resource Limitations ........................................................................................................15 Plant-Soil Feedbacks .......................................................................................................16 Major Functional Groups ..........................................................................................................17 Background .......................................................................................................................17 Vegetation ..........................................................................................................................18 Soil Biota ............................................................................................................................19 Biological Soil Crusts .......................................................................................................19 Invertebrate and Vertebrate Consumers ......................................................................22 Natural Disturbance Regimes .................................................................................................27 Background .......................................................................................................................27 Extreme Climatic Events ..................................................................................................27 Fire .......................................................................................................................................27 Insect and Disease Outbreaks .......................................................................................30 Herbivory and Trampling ..................................................................................................30 Landscape-Level Relationships ..............................................................................................31 Predominant Anthropogenic Stressors ..........................................................................................33 Visitor Use ...................................................................................................................................33 Livestock and Other Large Herbivores ...................................................................................33 Fire-Regime Alteration ..............................................................................................................33 Invasive Exotic Plants ...............................................................................................................33 Adjacent Land use Activities ...................................................................................................34 Air Pollutants ..............................................................................................................................34 Global Atmospheric Changes ..................................................................................................34 Ecosystem Dynamics ..................................................................................................................................37 Background—Alternative Ecosystem States ................................................................................37 Common Pathways and Processes of Dryland Degradation ......................................................37 iv Transition 1—Exotic Plant Invasion ........................................................................................39 Transition 2—Woody Plant Encroachment/Thickening ......................................................40 Transition 3—Soil Erosion/Redistribution ..............................................................................42 Transition 4—Soil Erosion/Redistribution ..............................................................................45 Transition 5—Exotic Conversion .............................................................................................46 Transition 6—Exotic Conversion .............................................................................................47 Transition 7—Soil Erosion/Redistribution .............................................................................48 Ecosystem Susceptibility to Change ...............................................................................................48 Ecosystem Exposure .................................................................................................................48 Ecosystem Resistance and Resilience ..................................................................................49 Implications for Ecosystem Classification .............................................................................49 Conclusion.....................................................................................................................................................51 References ....................................................................................................................................................51 Figures 1. Map showing mean annual precipitation and mean seasonal precipitation for National Weather Service Cooperative Network stations located at or near NPS units of the Southern and Northern Colorado Plateau Networks ...............................7 2. Map showing location of NCPN and SCPN parks
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