Historical Range of Variation Assessment for Wetland and Riparian Ecosystems, U.S. Forest Service Rocky Mountain Region Edward Gage and David J. Cooper United States Department of Agriculture / Forest Service Rocky Mountain Research Station General Technical Report RMRS-GTR-286WWW April 2013 Gage, Edward; Cooper, David J. 2013. Historical range of variation assessment for wetland and riparian ecosystems, U.S. Forest Service Rocky Mountain Region. Gen. Tech. Rep. RMRS-GTR-286WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 239 p. Abstract This document provides an overview of historical range of variation concepts and explores their application to wetland and riparian ecosystems in the US Forest Service Rocky Mountain Region (Region 2), which includes National Forests and National Grasslands occurring in the states of Colorado, Wyoming, Nebraska, Kansas, and South Dakota. For each of five ecosystem types—riparian areas, fens, wet meadows, salt flats, and marshes—we review key structural and functional characteristics including geomorphic setting, principal ecological drivers, classification, and dominant vegetation. In addition, we discuss anthropogenic factors known to influence the abundance or condition of each main wetland type. Keywords: wetlands, wet meadows, fens, salt flats, riparian, marshes, Colorado, Wyoming, South Dakota, Kansas, Nebraska Acknowledgments We thank the numerous individuals who provided us information, data, or critical review of this document including Barry Johnston, Bernie Bornong, Carl Chambers, Dave Bradford, Deanna Reyher, Dennis Lowry, Gay Austin, Greg Schenbeck, Jeff Redder, Jim Maxwell, Joe Neal, Joe Rocchio, Kathy Carsey, Ken Kanaan, Les Dobson, Les Gonyer, Michele Girard, Ray Zubick, Dave Ode, Gerry Steinauer, George Jones, Kelly Kindscher, Dean Erhard, Mike Johnson, Joanna Lemly, Kathy Roche, Rod Chimner, John Proctor, and Mike Menaffe. Claudia Regan, Jim Maxwell, and Dan Binkley were particularly helpful in seeing this project through from start to end. Special thanks to Kate Dwire and Melinda Larson for assistance in final revisions and facilitating publication. We also thank Kathy Roche, Gay Austin, and five anonymous reviewers from the Ecological Society of America for providing insightful comments on draft versions of this document. Historical Range of Variation Assessment for Wetland And Riparian Ecosystems, U.S. Forest Service Rocky Mountain Region Edward Gage and David J. Cooper Contents 1. Introduction................................................ 1 Objectives of the Project.....................................1 Organization of This Report ..................................5 Historical Range of Variation Concepts ........................5 Wetland Definitions and Applicable Laws.......................5 2. Data and Information Sources ................................ 8 Instrumental Records .......................................8 Paleoclimatic, Paleohydrologic, and Paleoecological Studies .....10 Classification of Region 2 Wetlands and Riparian Communities ...11 Historical Photographs and Accounts.........................12 3. Wetland and Riparian Ecosystems of Region 2: Structural and Functional Characteristics and Ecological and Historical Setting ....................................... 13 Introduction ..............................................13 Overview of the Principal Wetland and Riparian Types in the Region ..........................................14 Vegetation of Region 2 Wetlands and Riparian Areas ............17 Climate ..................................................19 Geomorphology and Geology ...............................26 Hydrologic Drivers of Wetland and Riparian Ecosystem Structure and Function ...............................28 Disturbance Regimes ......................................30 Ecoregions of Region 2.....................................31 Human History of the Region ................................31 Overview of Anthropogenic Impacts to Wetlands and Riparian Ecosystems .................................38 4. Historical Range of Variation for Region 2 Riparian Ecosystems ... 49 Definitions and Concepts of Riparian . .49 Geomorphic Setting and Principal Ecological Drivers ...........49 Riparian Classification and Gradients.........................57 HRV of Riparian Ecosystems in Region 2 ......................64 Management Opportunities and Constraints ...................90 5. Historical Range of Variation for Region 2 Marshes.............. 95 Definitions and Concepts of Marshes .........................95 Geomorphic Setting and Principal Ecological Drivers ...........95 Marsh Classification and Gradients..........................103 Marsh Vegetation in the Region .............................106 HRV of Marshes in Region 2................................108 Management Opportunities and Constraints ..................117 6. Historical Range of Variation for Region 2 Fens ................ 120 Definitions and Concepts of Fens . .120 Geomorphic Setting and Principal Ecological Drivers ..........121 Fen Classification and Gradients............................138 Fen Vegetation in the Region ...............................142 HRV of Fens in Region 2 ...................................146 Management Opportunities and Constraints ..................161 7. Historical Range of Variation for Region 2 Salt Flats . 166 Definitions and Concepts of Salt Flats .......................166 Geomorphic Setting and Principal Ecological Drivers ..........166 Salt Flat Classification and Gradients ........................174 Salt Flat Vegetation in the Region ...........................176 HRV of Salt Flats in Region 2 ...............................178 Management Opportunities and Constraints ..................181 8. Historical Range of Variation for Region 2 Wet Meadows ........ 184 Definitions and Concepts of Wet Meadows ...................184 Geomorphic Setting and PrincipalEcological Drivers ...........184 Wet Meadow Classification and Gradients ....................190 Wet Meadow Vegetation in the Region .......................192 HRV of Wet Meadows in Region 2 . .195 9. Conclusions ............................................. 203 References . 205 1. Introduction Objectives of the Project ________________________ Although they comprise only a small percentage of the region’s land area, wet- land and riparian ecosystems are critical components of Rocky Mountain and Great Plains landscapes. These ecologically diverse ecosystems are found at all elevations and latitudes and provide a number of important economic and eco- logical functions (Gregory and others 1991; Mitsch and Gosselink 2007; Patten 1998). Critical as wildlife habitat (Brown and others 1996; Davidson and Knight 2001; Haukos 1992; Nelson and others 1984) and as local and regional centers of biodiversity (Naiman and others 1993; Nilsson and Svedmark 2002; Pollack 1998), these ecosystems support many biogeochemical, physical, and ecological processes not found elsewhere on western landscapes. As wetland and riparian functions and values have become better understood, a variety of laws and regulations have been promulgated that are aimed at pro- moting wetland and riparian conservation. However, wetland and riparian areas have historically been heavily impacted by anthropogenic activities throughout North America (Brinson and Malvarez 2002; Graf 1999; Office of Technology Assessment 1984; Shafroth and others 1998; Tiner 1984). Demand for water, fertile land, and forage for livestock in the arid and semi-arid West has already affected many aquatic, riparian, and wetland areas; and pressures will likely in- crease with time, threatening the integrity and long-term viability of these vital ecosystems and the biota they support (Baron and others 2002; Pringle 2000). As a principal land manager in the region, the U.S. Department of Agriculture, Forest Service (USFS) sits at the center of this conflict. Charged with simultane- ously providing natural resources goods and services and conserving biodiversity and ecosystem integrity, the USFS must balance these often conflicting goals—a task that is made more difficult by the complexity of the social, economic, and ecological systems involved (Kaufmann and others 1994; Landres and others 1999). Recognizing this complexity, managers have increasingly looked to the scientific community to help inform and guide management and planning activi- ties (Dale and others 2000; Thomas 1996). Over the last several decades, a paradigm shift has occurred in the field of ecology, from a focus on stability and equilibrium, to an emphasis on concepts of variability, change, and dynamism (Holling 1996; Holling and Meffe 1996). Scientists have increasingly stressed the importance of disturbances to ecologi- cal systems (Turner and others 1996, 1998), and in response, managers have begun to apply such concepts to both individual species conservation efforts and broad-scale land management (Dale and others 2000). New conceptual and quantitative tools have been developed to relate ecological pattern to process at USDA Forest Service Gen. Tech. Rep. RMRS-GTR-286WWW. 2013 1 different spatial and temporal scales (Turner 1989), often with an explicit focus on system variability. One concept that is increasingly relied upon to guide land management activities is the historical range of variability (HRV). Our primary objective in this assessment is to apply this concept, defined and described be- low, to riparian and wetland ecosystems