Historical Range Of Variation Assessment For Wetland And .
Historical Range of Variation Assessmentfor Wetland and Riparian Ecosystems,U.S. Forest Service Rocky Mountain RegionEdward Gage and David J. CooperUnited States Department of Agriculture / Forest ServiceRocky Mountain Research StationGeneral Technical Report RMRS-GTR-286WWWApril 2013
Gage, Edward; Cooper, David J. 2013. Historical range of variation assessment for wetlandand 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, RockyMountain Research Station. 239 p.AbstractThis document provides an overview of historical range of variation concepts and explorestheir application to wetland and riparian ecosystems in the US Forest Service Rocky MountainRegion (Region 2), which includes National Forests and National Grasslands occurring in thestates of Colorado, Wyoming, Nebraska, Kansas, and South Dakota. For each of five ecosystemtypes—riparian areas, fens, wet meadows, salt flats, and marshes—we review key structural andfunctional characteristics including geomorphic setting, principal ecological drivers, classification,and dominant vegetation. In addition, we discuss anthropogenic factors known to influence theabundance or condition of each main wetland type.Keywords: wetlands, wet meadows, fens, salt flats, riparian, marshes, Colorado, Wyoming, SouthDakota, Kansas, NebraskaAcknowledgmentsWe thank the numerous individuals who provided us information, data, or critical review of thisdocument including Barry Johnston, Bernie Bornong, Carl Chambers, Dave Bradford, DeannaReyher, Dennis Lowry, Gay Austin, Greg Schenbeck, Jeff Redder, Jim Maxwell, Joe Neal, JoeRocchio, Kathy Carsey, Ken Kanaan, Les Dobson, Les Gonyer, Michele Girard, Ray Zubick, DaveOde, 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, andDan Binkley were particularly helpful in seeing this project through from start to end. Special thanksto Kate Dwire and Melinda Larson for assistance in final revisions and facilitating publication. Wealso thank Kathy Roche, Gay Austin, and five anonymous reviewers from the Ecological Societyof America for providing insightful comments on draft versions of this document.
Historical Range of Variation Assessment for Wetland AndRiparian Ecosystems, U.S. Forest Service Rocky Mountain RegionEdward Gage and David J. Cooper
Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Objectives of the Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Organization of This Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Historical Range of Variation Concepts . . . . . . . . . . . . . . . . . . . . . . . . 5Wetland Definitions and Applicable Laws . . . . . . . . . . . . . . . . . . . . . . 52. Data and Information Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Instrumental Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Paleoclimatic, Paleohydrologic, and Paleoecological Studies . . . . 10Classification of Region 2 Wetlands and Riparian Communities . . 11Historical Photographs and Accounts . . . . . . . . . . . . . . . . . . . . . . . . 123. Wetland and Riparian Ecosystems of Region 2: Structuraland Functional Characteristics and Ecological andHistorical Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Overview of the Principal Wetland and Riparian Types inthe Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Vegetation of Region 2 Wetlands and Riparian Areas . . . . . . . . . . . 17Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Geomorphology and Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Hydrologic Drivers of Wetland and Riparian EcosystemStructure and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Disturbance Regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Ecoregions of Region 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Human History of the Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Overview of Anthropogenic Impacts to Wetlands andRiparian Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384. Historical Range of Variation for Region 2 Riparian Ecosystems . . . 49Definitions and Concepts of Riparian . . . . . . . . . . . . . . . . . . . . . . . . . 49Geomorphic Setting and Principal Ecological Drivers . . . . . . . . . . . 49Riparian Classification and Gradients . . . . . . . . . . . . . . . . . . . . . . . . 57HRV of Riparian Ecosystems in Region 2 . . . . . . . . . . . . . . . . . . . . . 64Management Opportunities and Constraints . . . . . . . . . . . . . . . . . . . 905. Historical Range of Variation for Region 2 Marshes . . . . . . . . . . . . . . 95Definitions and Concepts of Marshes . . . . . . . . . . . . . . . . . . . . . . . . 95Geomorphic Setting and Principal Ecological Drivers . . . . . . . . . . . 95Marsh Classification and Gradients . . . . . . . . . . . . . . . . . . . . . . . . . 103Marsh Vegetation in the Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106HRV of Marshes in Region 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Management Opportunities and Constraints . . . . . . . . . . . . . . . . . . 117
6. Historical Range of Variation for Region 2 Fens . . . . . . . . . . . . . . . . 120Definitions and Concepts of Fens . . . . . . . . . . . . . . . . . . . . . . . . . . . 120Geomorphic Setting and Principal Ecological Drivers . . . . . . . . . . 121Fen Classification and Gradients . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Fen Vegetation in the Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142HRV of Fens in Region 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146Management Opportunities and Constraints . . . . . . . . . . . . . . . . . . 1617. Historical Range of Variation for Region 2 Salt Flats . . . . . . . . . . . . 166Definitions and Concepts of Salt Flats . . . . . . . . . . . . . . . . . . . . . . . 166Geomorphic Setting and Principal Ecological Drivers . . . . . . . . . . 166Salt Flat Classification and Gradients . . . . . . . . . . . . . . . . . . . . . . . 174Salt Flat Vegetation in the Region . . . . . . . . . . . . . . . . . . . . . . . . . . . 176HRV of Salt Flats in Region 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178Management Opportunities and Constraints . . . . . . . . . . . . . . . . . . 1818. Historical Range of Variation for Region 2 Wet Meadows . . . . . . . . . 184Definitions and Concepts of Wet Meadows . . . . . . . . . . . . . . . . . . . 184Geomorphic Setting and PrincipalEcological Drivers . . . . . . . . . . 184Wet Meadow Classification and Gradients . . . . . . . . . . . . . . . . . . . 190Wet Meadow Vegetation in the Region . . . . . . . . . . . . . . . . . . . . . . . 192HRV of Wet Meadows in Region 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . 1959. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
1. IntroductionObjectives of the ProjectAlthough they comprise only a small percentage of the region’s land area, wetland and riparian ecosystems are critical components of Rocky Mountain andGreat Plains landscapes. These ecologically diverse ecosystems are found at allelevations and latitudes and provide a number of important economic and ecological functions (Gregory and others 1991; Mitsch and Gosselink 2007; Patten1998). Critical as wildlife habitat (Brown and others 1996; Davidson and Knight2001; Haukos 1992; Nelson and others 1984) and as local and regional centersof biodiversity (Naiman and others 1993; Nilsson and Svedmark 2002; Pollack1998), these ecosystems support many biogeochemical, physical, and ecologicalprocesses 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 promoting wetland and riparian conservation. However, wetland and riparian areashave historically been heavily impacted by anthropogenic activities throughoutNorth America (Brinson and Malvarez 2002; Graf 1999; Office of TechnologyAssessment 1984; Shafroth and others 1998; Tiner 1984). Demand for water,fertile land, and forage for livestock in the arid and semi-arid West has alreadyaffected many aquatic, riparian, and wetland areas; and pressures will likely increase with time, threatening the integrity and long-term viability of these vitalecosystems 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 simultaneously providing natural resources goods and services and conserving biodiversityand ecosystem integrity, the USFS must balance these often conflicting goals—atask that is made more difficult by the complexity of the social, economic, andecological systems involved (Kaufmann and others 1994; Landres and others1999). Recognizing this complexity, managers have increasingly looked to thescientific community to help inform and guide management and planning activities (Dale and others 2000; Thomas 1996).Over the last several decades, a paradigm shift has occurred in the field ofecology, from a focus on stability and equilibrium, to an emphasis on conceptsof variability, change, and dynamism (Holling 1996; Holling and Meffe 1996).Scientists have increasingly stressed the importance of disturbances to ecological systems (Turner and others 1996, 1998), and in response, managers havebegun to apply such concepts to both individual species conservation effortsand broad-scale land management (Dale and others 2000). New conceptual andquantitative tools have been developed to relate ecological pattern to process atUSDA Forest Service Gen. Tech. Rep. RMRS-GTR-286WWW. 20131
different spatial and temporal scales (Turner 1989), often with an explicit focuson system variability. One concept that is increasingly relied upon to guide landmanagement activities is the historical range of variability (HRV). Our primaryobjective in this assessment is to apply this concept, defined and described below, to riparian and wetland ecosystems of the USFS Rocky Mountain Region(Region 2).Specifically, our goals are to: (1) outline the types of wetland and riparian ecosystems that occur on Region 2 National Forests and Grasslands; (2) identify andcharacterize the key variables driving vegetation patterns and functional attributesof wetlands and riparian systems at a range of spatial and temporal scales; and(3) use available data and information to make inferences regarding the HRV ofkey variables influencing wetlands and riparian areas prior to the mid-nineteenthCentury when extensive Euro-American settlement in the region began. Unlikemost previous HRV assessments prepared for Region 2 (e.g., Dillon and others2005; Meyer and others 2003; Veblen and Donnegan 2005), the broad geographicscope of this assessment which encompasses 17 National Forests and 7 NationalGrasslands in 5 states (Figure 1) and high ecological and functional diversityof ecosystems in the assessment area preclude a fine-grained, spatially explicitanalysis for each Forest and Grassland. Rather, our intent is (1) to provide abroad conceptual framework based on the best available scientific informationFigure 1. National Forests and Grasslands in the U.S. Forest Service Rocky Mountain Region.USDA Forest Service Gen. Tech. Rep. RMRS-GTR-286WWW. 20132
from which managers or researchers can develop reasonable assessments of theHRV of wetlands or riparian systems in particular planning areas and (2) to provide a starting point for further site-specific research. There are many potentialvariables we could focus on, each operating at different spatial and temporalscales (Table 1), but our general emphasis is on variables operating at the scaleof individual wetlands to watersheds.Previous HRV Assessments in Region 2Most previous HRV assessments in Region 2 have been prepared for individualNational Forests and have been limited to upland forested ecosystem types (Dillonand others 2005; Kulakowski and Veblen 2006; Meyer and others 2003; Veblenand Donnegan 2005). Our overall objectives are similar to these assessments,but our focus is on a much broader geographic area and on multiple ecosystemtypes that differ widely in composition, structure, and function. These fundamental differences in scope among assessment efforts require the use of differentconceptual and analytical approaches.Even when applied in a qualitative rather than a quantitative statistical context,reference to a specific variable of interest is required for the HRV concept tohave meaning. A variety of ecological attributes were examined in previous HRVanalyses, spanning multiple spatial and temporal scales (Table 2). While our approach is similar, most of the specific ecological drivers and response variablesTable 1—Nested hierarchy of key spatial and temporal scales, ecological drivers, and ecological response variables relevant to thestructure and function of a hypothetical wetland. Our assessment is primarily focused on drivers and response variables.LevelTime (yr)ScaleSpace (m2)Key ecological driversPotential response variablesLeaf0.001 to 10.01 to 0.1Photosynthetically activeradiation; osmotic pressure;tissue nutrient concentrationsRespiration photosynthesisdecompositionPlant0.1 to 1000.1 to 10Soil water availability;nutrient concentrations;competition; herbivoryPlant productivity; root, shoot,and propagule productionWetland1 to 10001 to 1000Water table depth; localhydrology; herbivorySpecies diversity andproductivity; decomposition;N mineralization; peataccumulation rateWatershed100 to 10,0001000 to 10,000Mass wasting; bedrockporosity; glacial history;fire history; beaver;stream discharge;sediment productionDistribution and abundance ofdifferent wetland typesEcoregion 10,000 100,000Lithology; tectonics;Milankovitch cyclesAdaptation; extinction;species radiationUSDA Forest Service Gen. Tech. Rep. RMRS-GTR-286WWW. 20133
Table 2—Examples of ecological variables examined in previous HRV assessments (left column)and those variables discussed in this assessment (right column). Variables of particularimportance to specific ecosystem type(s) are indicated in parentheses (M marsh, WM wet meadow; F fen; R riparian; SF salt flat). Definitions and descriptions of ecosystemtypes are presented later in the document.Examples of ecosystem variablesexamined for upland HRVPotential ecosystem variables ofinterest in wetland/riparian HRVSnag density (Dillon et al. 2005)Species composition (M, WM, SF, F, R)Stand structure (Dillon et al. 2005)Age-class distribution (R, WM)Tree species and genetic diversity(Dillon et al. 2005)Proportion woody cover (WM, F, R)Tree density (Dillon et al. 2005)Woody plant size/age distribution (WM, R)Density and size of canopy gaps(Dillon et al. 2005)Wetland abundance (M, WM, SF, F, R)Density and cover of understory plants(Dillon et al. 2005)Landscape diversity of wetland types(M, WM, SF, F, R)Age-class structure of stands(Dillon et al. 2005)Flood frequency, magnitude, & timing(M, WM, SF, F, R)Size-class structure of stands(Dillon et al. 2005)Course woody debris (R)Course woody debris (Dillon et al. 2005)Beaver abundance and use (R)Seedling and sapling density (Dillon et al. 2005)Sediment budget (M, WM, SF, F, R)Fire (Dillon et al. 2005; Veblen andDonnegen 2003)Carbon accumulation/loss dynamics (F)Disease (Dillon et al. 2005; Veblen andDonnegen 2003)Hydrologic variability (M, WM, SF, F, R)Insects (Dillon et al. 2005; Veblen andDonnegen 2003)Spatial and temporal patterns of woodyplant establishment (WM, R)Wind (Dillon et al. 2005; Veblen andDonnegen 2003)Ground and surface water chemistry,nutrient fluxes (M, WM, SF, F, R)Wetland functions (groundwater recharge,discharge, biodiversity, storm waterdetention, etc.) (M, WM, SF, F, R)for wetland and riparian ecosystems differ from those of upland forests. Evenamong wetland types, the most important variables may differ. For instance, shallow groundwater inflow is a key variable driving vegetation dynamics in fens,wet meadows, and some marshes (Galatowitsch and van der Valk 1998; Winter1999; Winter and Rosenberry 1995), however it is not a critical driver of GreatPlains riparian communities along ephemeral streams, which are influenced moreby infrequent floods (Friedman and Lee 2002). Species composition can differalmost completely between two nearby fens within the same small watershed,but can be identical between cattail (Typha spp.) marshes hundreds of milesdistant from one another. Variables examined in this and previous assessmentsare contrasted in Table 2 and are discussed in greater detail in chapters specificto each wetland type.USDA Forest Service Gen. Tech. Rep. RMRS-GTR-286WWW. 20134
Organization of This ReportA major challenge in preparing an assessment of this scope is to provide a conciseyet thorough framework in which to explore the ecological and historical factors shaping the HRV of different ecosystem types. In this chapter, we providean overview of our objectives and an introduction to some of the basic HRVconcepts and definitions used in earlier assessments and those we have appliedto wetlands and riparian ecosystems in this document. In Chapter 2, we outlinethe primary resources and analytical approaches we used in assessing the HRVfor wetland and riparian ecosystems. Many topics, such as broad-scale climatictrends and the human history of different parts of the study region are presentedin Chapter 3, along with a review of wetland and riparian classifications. Subsequent chapters present an HRV assessment for each of the five major wetlandand riparian ecosystem types that occur in USFS Region 2: riparian ecosystems,marshes, fens, salt flats, and wet meadows. In Chapter 8, we provide a synthesisof our findings and present suggestions for future research.Historical Range of Variation ConceptsThe underlying premise of the HRV approach is that by managing ecosystemsfor the range of processes that have characterized ecosystems in the past, landmanagers can maximize the likelihood of preserving into the future the widestcompliment of species and important ecological functions (Landres and others1999; Veblen 2003). Several closely related terms have been applied by previousauthors, including “range of natural variability,” “reference variability” (Manleyand others 1995),“natural variability” (Landres and others 1999), and “historicrange of variability” (Dillon and others 2005; Meyer and others 2003; Morganand others 1994; Veblen 2003). Common to all of these definitions is an explicitrecognition of the dynamic nature of ecological systems and the necessity ofanalyzing ecosystems at multiple scales. Our HRV definition closely followsearlier ones: the spatial and temporal variation in key ecosystem processes andcharacteristics prior to major alteration by Euro-Americans—approximatelythe mid- to late-1800s for most of the region. Spatial and temporal scales mustbe explicitly discussed because there are differences in the timing and natureof initial E
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
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