° WATER RESOURCES BULLETIN VOL. 31, NO. 3 AMERICAN WATER RESOURCES ASSOCIATION JUNE 1995
WATERSHED ANALYSIS AS A FRAMEWORK FOR IMPLEMENTING ECOSYSTEM MANAGEMENT
David R. Montgomery, Gordon E. Grant, and Kathleen Sullivan2
ABSTRACT: Implementing ecosystem approaches to land use deci- scientifically founded strategies for managing ecosys- sion making and land management requires new methods for link- tems, in spite of the dependence of individual species ing science and planning. Greater integration is crucial because under ecosystem management sustainable levels of resource use viability on ecosystem-scale processes. The continuing are determined by coupling management objectives to landscape practice of managing or protecting primarily on an capabilities and capacities. Recent proposals for implementing ownership-, site-, or species-specific basis emphasizes ecosystem management employ analyses organized at a hierarchy both short-term economic perspectives and localized of scales for analysis and planning. Within this hierarchy, water- consideration of environmental degradation. Hence, shed analysis provides a framework for delineating the spatial dis- tribution and linkages between physical processes and biological the integrated effects of local management decisions communities in an appropriate physical context: the watershed. can be incompatible with broader-scale management Several such methods are currently in use in the western United objectives. Despite dramatic increases in the effort States, and although there is no universal procedure for either and expenditure for environmental protection over implementing watershed analysis or linking the results to plan- the past 20 years, the overall condition of natural ning, there are a number of essential elements. A series of ques- tions on landscape-level ecological processes, history, condition, and ecosystems generally continues to decline. This funda- response potential guide watershed analysis. Individual analysis mental flaw in linking land management objectives modules are structured around answering these questions through and practice set up inevitable legal confrontations pit- a spatially-distributed, process-based approach. The planning ting species survival against resource use, giving the framework linked to watershed analysis uses this information to false perception that they are incompatible. A new either manage environmental impacts or to identify desired condi- tions and develop land management prescriptions to achieve these land management paradigm, loosely termed ecosys- conditions. Watershed analysis offers a number of distinct advan- tem management (e.g., Slocombe, 1993), seeks to rec- tages over contemporary environmental analyses for designing land oncile this paradox by applying an ecological management scenarios compatible with balancing environmental perspective to addressing land use and environmental and economic objectives. degradation. Implementing ecosystem management, (KEY TERMS: watershed analysis; ecosystem management; water- shed management; environmental planning.) however, requires a framework for gathering and interpreting environmental information at a resolu- tion, scope, and scale necessary for addressing the tradeoffs between economic and ecological considera- INTRODUCTION tions inherent to making land management decisions.
Societal concern over the historical degradation of Ecosystem Management natural ecosystems and resources once considered inexhaustible resulted in laws intended to provide some ecological safeguards (e.g., ESA, 1973; Ecosystem management is founded on the principle NEPA, 1982; NFMA, 1982). Laws intended to protect of preserving ecosystem integrity while maintaining species, however, were established independent of sustainable benefits for human populations (see
1Paper No. 94076 of the Water Resources Bulletin. Discussions are open until February 1, 1996. 2Respectively, Research Assistant Professor, Department of Geological Sciences, University of Washington, Seattle, Washington 98195; USDA Forest Service, PNW Research Station, 3200 Jefferson Way, Corvallis, Oregon 97331; and Weyerhaeuser Technology Center, Weyer- haeuser Company, Tacoma, Washington 98477. 369 WATER RESOURCES BULLETIN
Montgomery, Grant, and Sullivan
Norton, 1992). Ecosystem management thus presup- plans for modifying landscape processes to better suit poses land use will occur, although it assumes neither human desires or for identifying thresholds that trig- the location nor intensity of any particular activity. ger land use restrictions. In contrast, ecosystem man- Preserving ecosystem integrity, however, involves sus- agement requires a proactive approach to taining naturally reproducing populations of all environmental impact mitigation, an argument species. Ecosystem management therefore involves a advanced by Leopold (1934) as the most cost-effective fundamental restructuring of historical practices of societal approach to managing soil erosion. This land use planning and decision making based on eval- requires input management through identifying the uating the impacts of individual projects. Several impacts of human actions on ecological processes and additional principles provide the basis for implement- systems, and redesigning land use and management ing ecosystem management. The most important of to minimize these impacts [see also discussion by these involves tailoring land management to land- Montgomery (1995)]. In short, it focuses on treating scape conditions, processes and potential. This causes rather than symptoms of environmental degra- involves defining the intrinsic capabilities and limita- dation. This approach requires process-oriented anal- tions of different parts of the landscape to support a yses rather than the threshold-based and blind particular suite or style of activities. A related concept sampling approaches used in most current watershed is acknowledging the variable capacity of different management and monitoring programs. Only by parts of the landscape to sustain those activities developing a process-oriented understanding of how a through time and the potential for some disturbances landscape works in a spatially-distributed context can or impacts to propagate downslope and downstream. we begin to develop effective input-oriented approach- A wealth of historical examples support the thesis es at the landscape scale. While this already is done that ignoring the relation between land use and the for some projects, ecosystem management provides a intrinsic capability and capacity of the land invites unified framework for implementing such an dire long-term consequences for both ecosystems and approach at larger scales. human societies (e.g., Marsh, 1864; Carter and Dale, A key element of any decision-making system that 1955; Thomas, 1956). involves consideration of both economic and ecological Tailoring land management to the landscape resource management objectives is a broader land- requires a more symbiotic relationship between sci- scape-scale context for developing an understanding ence and land use planning (Leopold, 1933). At pre- of interacting environmental and ecological processes. sent scientific expertise is principally used to achieve, Such a framework should be founded on using analy- rather than define, land management objectives by ses organized around ecologically relevant units to altering landscape capabilities to provide desired com- guide planning and implementing management activ- modity production. Under ecosystem management, ities. Ecosystem management therefore must consider science precedes planning and analyses are oriented physical and biological interactions occurring over around resources rather than potential projects. This spatial scales ranging from individual organisms up involves expanding the role of science to include eval- to entire regions. This can be considered to involve uating alternative management scenarios against analyses at four distinct spatial scales: region, intrinsic landscape capabilities to mold societal expec- province, watershed, and project (FEMAT, 1993). A tations to the landscape. Scientific methods are essen- region represents a broadly defined area, such as the tial to assessing landscape capacity, often complex Pacific Northwest, that encompasses several physio- and interwoven with a legacy of natural and anthro- graphic provinces (Fenneman, 1931) or ecoregions pogenic disturbances. Such understanding is essential (Omernik, 1987) across multiple states. Regional- for informed management decisions. Hence, planning scale issues may include biodiversity (Noss, 1983), needs to recognize the spatial and temporal scales economic and social expectations, and patterns of over which natural systems operate (Odum, 1969; public and private ownership. Provinces cover areas Caldwell, 1970). This represents a fundamental on the order of 1000s of square miles and are defined change from planning based on political or adminis- by either major drainage basins or collections of trative units, and it requires broadening planning smaller basins (e.g., small coastal watersheds). horizons to include multiple ownerships, land uses, Province-scale issues include: (1) impacts of large- and interests, a goal difficult to achieve under the scale water development (i.e., hydropower and agri- current legal and regulatory system. cultural water diversions); (2) historical and future A variety of regional planning protocols are applied urbanization and land use patterns; and (3) distribu- to environmental management, particularly for devel- tions of some threatened and endangered species. In opment and flood control issues. These analyses many landscapes, watersheds covering approximately rarely if ever tailor land use to the landscape. Rather, 20 to 200 square miles are practical analysis and they generally are oriented toward either developing planning units within provinces. Watershed analysis
WATER RESOURCES BULLETIN 370 Watershed Analysis as a Framework for Implementing Ecosystem Management
at this scale allows landscape-specific assessment of management on state and private (WFPB, 1992; the status of and linkages between physical and bio- 1993) and federal (FEMAT, 1993) lands in the Pacific logical resources and processes. At finer scales, it Northwest. These approaches are still evolving and becomes difficult to represent relevant processes and may differ in their management objectives; while connect upstream causes to downstream effects; at watershed analysis provides a more complete under- broader scales, data interpretation and assimilation standing of landscape-scale processes, balancing eco- become impractical. The finest scale of planning nec- nomic and ecological priorities lies within the realm of essary for ecosystem management involves specific planning. Simply put, watershed analysis is intended sites where management actions are implemented. to provide the information required to assess such While consideration of this full range of scales is nec- trade offs and develop land management plans for essary to encompass the spatial and temporal dynam- implementing policies that are consistent with meet- ics of human influences on environmental processes ing management objectives. Coupled to landscape- and resources (Preston and Bedford, 1988), analyses level planning processes, watershed-scale analyses at these different scales could be based on modifying can provide a framework for generating the informa- the basic framework developed here. tion required to accountably assess performance Analyses and decision making at each of these toward achieving environmental objectives, in much scales reflects issues, information, and constraints the same manner that other systems are set up to inherited from other levels of the hierarchy. Regional measure and evaluate economic success. issues, for example, define a broad template against Development of a common framework would facili- which land management prescriptions are made and tate integration of results across multiple ownership decisions evaluated at the province scale, which in boundaries, provide a framework for balancing turn influences management decisions at the water- economic and ecological objectives, and thereby con- shed scale. Each of these scales of analysis and plan- tribute toward avoiding situations where manage- ning are necessary for implementing ecosystem ment results are inconsistent with management management because: (1) the distribution and envi- objectives. Here we describe the philosophy and prin- ronmental requirements of a number of species are ciples that underlie watershed analysis, define the not organized on a watershed basis, and thus need to essential components and general approach, and dis- be considered across levels of the analysis and plan- cuss key linkages to the planning process. Recogniz- ning hierarchy; and (2) the spatial context within ing that there likely will be many approaches to which a watershed lies is an important factor in eval- watershed analysis (e.g., WFPB, 1992; FEMAT, 1993: uating the ecological significance of land management USDA, 1994), our intent is both to define a set of cri- alternatives. Watershed-scale analyses provide the teria essential to any method and to discuss advan- fundamental units structuring the planning hierar- tages of and impediments to using watershed analysis chy, as watershed-specific information defines the to implement ecosystem management. context for individual projects and can be aggregated as needed to provide information for decision making at the province and regional scales. EVOLUTION OF WATERSHED ANALYSIS
Watershed-Scale Analysis The concept of watershed-based analysis and plan- ning is not new (see review in Schramm, 1980), and Although a number of recent initiatives and strate- many previous approaches to land management have gies focus on larger-scales and a broader scope incorporated one or more of the principles outlined (WFPB, 1992; FEMAT, 1993; SAT, 1993), there is not above (Table 1). The ancient Chinese art of geomancy, yet consensus on how to implement ecosystem man- for example, emphasized the interpretation of land- agement. A key element is development of a practical forms as the basis for siting buildings and other operational framework for integrating ecosystem human activities (Pennick, 1979). In the United management into land use decision making. Water- States, the Organic Act of 1897 establishing the sheds define basic, ecologically and geomorphological- National Forest system implicitly recognized the ly relevant management units (Chorley, 1969; Likens importance of tailoring land use to landscape capabili- and Bormann, 1974; Lotspeich, 1980) and watershed ty when it gave equal weight to timber harvest and analysis provides a practical analytical framework for securing "favorable conditions of flow" (Steen, 1976). spatially-explicit, process-oriented scientific assess- More recent approaches have also incorporated a ment that provides information relevant to guiding watershed basis for planning. In the 1930s, the management decisions. Recently, watershed analysis National Planning Board developed river basin man- has been adopted to implement ecosystem-oriented agement schemes (e.g., Tennessee Valley Authority)
371 WATER RESOURCES BULLETIN Montgomery, Grant, and Sullivan
TABLE 1. Examples of Landscape-Level Analyses and Planning Incorporating Elements of Ecosystem Management. Tailor Based on Decisions to Protect Science Flexible Ecologically Considers Relevant Landscape Ecosystem Precedes and Multiple Capabilities Integrity Planning Iterative Units Scales River Basin Plans (ca 1930s) 0 0 0 0 U.S. Forest Service Unit Plans 0 USFS Forest Plans 0 - 0 0
Cumulative Effects Analysis 0 0 x X 0
Watershed Analysis 0 x x x X Ecosystem Management x x x X
X = Central to approach. — = Addressed but not central. 0 = Not addressed.
and pioneered regional land use planning (Platt, from procedural inconsistencies, inadequate technical 1991). A number of subsequent river basin plans foundations, and difficulties incorporating results into developed for large transnational rivers (e.g., Mekong, planning (Craig, 1987; FEMAT, 1993); none incorpo- Senegal, Rio de la Plata) encountered political prob- rated all of the principles underlying ecosystem man- lems that hampered implementation (Schramm, agement. 1980). In the mid-1960s, U.S. Forest Service At this time, watershed analysis has been researchers called for watershed-based hydrological embraced by several processes exploring its use for analysis to guide forest land use planning (Megahan, implementing ecosystem management. Watershed 1965). Unit Plans employed by the U.S. Forest Ser- analysis is currently applied voluntarily on forested vice until the mid-1970s often were defined by water- watersheds of 50-200 km 2 in Washington (WFPB, shed boundaries although they did not systematically 1992), and an expanded version is one component of a address ecological considerations in determining lev- proposed framework for implementing ecosystem els of resource extraction, which were driven by tim- management on federal lands (FEMAT, 1993). Both of ber quotas imposed on a forest by forest basis. Forest these approaches are still evolving, but to date 22 Plans developed in response to the 1976 National For- watersheds have been analyzed under the Washing- est Management Act (NFMA, 1982) attempted to ton State program. Numerous local watershed initia- address a broader range of ecological issues, but tives developing around the western United States analyses were typically limited by administrative also integrate some of the principles outlined above. boundaries. This evolution of approaches to land man- agement coincided with increasing conflict over inten- sive resource use in the western United States. The most direct precursors of watershed analysis FRAMEWORK FOR WATERSHED ANALYSIS methods are procedures developed over the past sev- eral decades to address the cumulative effects of land Watershed analysis provides a means to resolve a management. Many of the techniques for assessing number of problems that plagued previous efforts to cumulative effects were developed by land managers integrate an understanding of physical and biological charged with evaluating the combined impact of mul- processes into land use planning. In the past, much of tiple activities under the 1969 National Environmen- the available scientific knowledge was not applied tal Policy Act (NEPA, 1982) and subsequent Council effectively in the land management arena because: on Environmental Quality regulations (CEQ, 1971). (1) landscapes were not viewed as systems, so link- The need for a watershed-oriented approach to this ages among processes and landscape elements were issue (Coats and Miller, 1981) focused attention on not addressed; (2) planning processes lacked adequate linkages among watershed processes, biological sys- mechanisms for incorporating science directly into tems, and land management (see review by Reid, decision making, so new information was underuti- 1993). Many of these approaches, however, suffered lized; (3) many planning procedures relied on simple
WATER RESOURCES BULLETIN 372 Watershed Analysis as a Framework for Implementing Ecosystem Management
thresholds and uniform prescriptions to deal with assessments, historical analyses, and landscape-scale complex problems in highly variable landscapes; models of geomorphological and ecological processes. (4) information on current conditions was collected The framework for watershed analysis and plan- haphazardly and without a clear set of questions or ning consists of societal goals and desires brought to a hypotheses; (5) historical data and trends were large- place based on regional concerns or issues (Figure 1). ly ignored; and (6) no provisions were made to ade- The presence of the last spring chinook run in a quately test assumptions, results, or effects of region, for example, may constrain management management prescriptions. Watershed analysis is options within a watershed if preservation of the run intended to address these shortcomings by providing is either valued or mandated by law. Regional con- a systematic procedure for characterizing the physical cerns and issues thus provide the context for develop- and biological processes active within a watershed, ing land management prescriptions. Watershed their spatial distribution, history, and linkages; past analysis can be used to either minimize the impact of and current habitat and biological conditions; and the land management or to identify desired conditions linkages between landforms, surface processes, and and develop land management plans to achieve those biological systems. The information generated in a conditions. Under either approach, watershed analy- watershed analysis guides ecosystem-oriented land sis should collect the evidence and present the logic use planning and development of landscape-specific underlying land management decisions. management prescriptions, identifies and directs pri- oritization of restoration opportunities, and provides information necessary for developing efficient moni- toring programs. regional issues Watershed analysis provides a methodology for management objectives organizing analyses such that they can be both syn- thesized into larger regional pictures and provide con- text for developing site-specific designs and management expectations. This requires satisfying a research analysis modules number of criteria that differ from current analyses. Most importantly, this approach needs to address cause-and-effect linkages in a spatially distributed context because spatially aggregated approaches (e.g., equivalent clear cut area concept and multiple synthesis regression correlations between resource conditions and general descriptors of land use intensity) neglect the simple fact that identical actions located in differ- ent areas of a basin can have dramatically different social constraints impacts. Also, the role and significance of a particular laws planning monitoring process or resource depends not only on how big or extensive it is, but also on its location, the larger landscape within which it lies, and its relation and connections to other landscape components (e.g., Pre- ston and Bedford, 1988). Watershed analysis also implementation must be process oriented and hypothesis driven in order to establish cause-and-effect relations between management activity and environmental impacts. Figure 1. Schematic Illustration of the Context The historical legacy of past natural and anthro- for Watershed Analysis. pogenic processes and disturbance must be addressed because of the influence of past processes on current conditions and response potential. Field work and analyses are thus essential for establishing current The guiding philosophy behind watershed analysis conditions and evaluating potential hypotheses con- is that although a landscape and its ecosystems are cerning past influences. Hence, watershed analysis complex and impossible to understand or characterize cannot be an exclusively GIS-based exercise; neither completely, there is enough pattern to the linkages can it be based on simple correlation between within and between physical and ecological systems environmental indices and spatially aggregated indi- that we can develop reasonable models of how they cators of land management. Rather, watershed analy- interact. Watershed analysis provides a limited sis must rely on integrating field analyses and yet reasonably comprehensive assessment of these
373 WATER RESOURCES BULLETIN Montgomery, Grant, and Sullivan linkages and processes. The underlying assumption is achieve these goals. A plan is then selected and imple- that informed land management decisions require mented and the results monitored and compared with high-quality information focused on key processes and predicted progress toward achieving desired condi- linkages that create and shape ecosytems. Thus, one tions. of the most important aspects of watershed analysis is that it is limited in scope; we cannot hope to appreci- ate, let, alone understand, the full detail of system interactions. Hence, output-oriented management or STRUCTURE OF WATERSHED ANALYSIS monitoring is necessary to supplement the primary emphasis on input-oriented management and to Watershed analysis itself is structured around a assess whether management plans are achieving series of questions which, if answered, provide a management objectives (see also Montgomery, 1995). model of landscape and ecosystem function, distur- While this limited scope enables watershed analy- bance history, and current and potential future condi- sis to contribute to land use planning, it also raises tions (WFPA, 1992; 1993). A question-driven approach the possibility that key attributes or processes influ- is essential for developing landscape-specific, process- encing an ecosystem may be neglected. Consequently, based approaches to implementing input manage- watershed analysis methods and procedures must be ment because no simple rigid procedure or analysis both flexible and designed to be updated and revised will be appropriate in all landscapes or at all locations as new information or understanding of ecosystem within a watershed. This approach is similar to a pro- processes is either developed or becomes available. posed framework for addressing problems of land- The basic framework of watershed analysis (Figure 1) scape design (Steinitz, 1990). Answering these is fixed, but the structure of each component must be questions requires the talents and perspectives of an periodically revised and updated in order to use interdisciplinary team of physical and biological sci- watershed analysis to implement ecosystem manage- entists and planners. The procedure generates a trail ment. Watershed analysis can support any decision- of logic that connects analysis of landscape processes making priorities; it is intended only to generate the to subsequent management activity. information required to make informed choices about A critical issue is the level of analysis and resolu- potential land management impacts in a spatially-dis- tion needed to answer each question. There are no tributed context. Decision-making inherently involves a priori grounds to determine this; it will always incorporation and prioritization of many other soci- depend on the level of confidence desired for the anal- etal wants and needs. ysis, which in turn reflects acceptable risk. The ques- We describe a structure and method of watershed tion-driven approach is meant to guide and focus analysis first developed in Washington by a multi- analyses by using objective, analytical methods. stakeholder group and adopted by the Washington There can be no cookbook approach to watershed Forest Practices Board (1992), and then modified by analysis because landscapes are inherently variable other organizations to fit different management objec- and simple indices are not always relevant. We need tives. Watershed analysis consists of a series of analy- both solid conceptual bases and models within which sis modules that guide resource specialists through to work and highly trained, independent thinkers to logical procedures for assessing the physical and bio- work within these guidelines. Many other professions logical systems within a watershed. While the general (e.g., medicine and engineering) face similar dilem- framework and structure of these modules apply to all mas, and a common method for addressing this issue landscapes, the analysis methods should reflect the is to develop standards for state-of-the-art practices geomorphic and biological processes operating within that serve as reference points for judging individual a specific landscape. Products of the analysis modules analyses. While this implies some system of peer define conditions, trends, and potential conditions for review and professional oversight, the various physical and biological resources within the water- approaches to developing standards for implementing shed. Landscape-specific information on geomorphic watershed analysis are beyond the scope of this paper. and biological systems generated through analysis modules is then synthesized into a model of land- scape-scale ecological functions and interactions. This How Does This Landscape Work? synthesis guides identification of potential conditions and trade-offs between management activity and eco- Answering this question requires analysts to devel- logical conditions. Planning uses the information gen- op a model for the relations among landforms, physi- erated by a watershed analysis together with social cal processes, and biological factors governing the and institutional objectives and constraints to define ecosystems developed on a landscape. This approach desired resource conditions and develops plans to
WATER RESOURCES BULLETIN 374 Watershed Analysis as a Framework for Implementing Ecosystem Management promotes a system-level view of the dominant pro- characteristics such as channel pattern and substrate cesses and linkages controlling and influencing size. While this information conceivably could be col- ecosystem structure and dynamics. Realistic assess- lected at any level of detail, its usefulness depends on ment of resource conditions or probable responses to how well it describes the landscape in terms relevant management activity requires understanding of the to developing or testing models of landscape function. basic environmental template upon which biological Detailed species or habitat inventories, for example, systems develop (Southwood, 1977). We therefore are likely to be most useful if synthesized into habitat need to identify those parts of the landscape dominat- associations linked to vegetation or landforms. To be ed by different environmental processes or distur- useful, however, information collected must be either bance regimes. The disturbance regime defines the used in the analysis or provide baseline data for ongo- type of disturbances (i.e., fire, wind, flood, or land- ing monitoring. slide) and their frequency, spatial extent, and intensi- ty (Sousa, 1984; Swanson et al., 1993). We also need to understand the spatial linkages among landscape What are Trends in Watershed Condition? components because some processes or disturbances propagate through a landscape. Landslides originat- Comparing historical and current conditions pro- ing in steep hillside hollows, for example, can become vides the primary means of assessing changes in debris flows that scour steep downslope channels and landscapes and ecosystems. These trends can be deliver sediment to lower-gradient channels (e.g., expressed in terms of temporal changes in some mea- Costa, 1984; Benda, 1990). Ultimately, information on sure of either watershed or biologic condition (e.g., the spatial and temporal distribution of a variety of stand structure or composition, number of owls, width processes is necessary to identify sensitive or critical of riparian openings), or landscape processes (e.g., areas of the landscape. landslide rates, streamflow variability). Evaluating the role of human activities in these changes is What Has Happened in the Past? accomplished through categorizing trends by their likely causal mechanisms (e.g., distinguishing among rates of landsliding from roads, pristine forests, and Assessing the disturbance history of a landscape clear cuts). provides a context within which to interpret current conditions and evaluate potential disturbance pat- terns. One of the precepts of ecosystem management How Sensitive is the Ecosystem to Future Land is that ecosystem stress increases with deviation from Management? the disturbance regime under which the ecosystem evolved (Sousa, 1984; Swanson et al., 1993). This Answering this question is crucial for assessing implies that knowledge of historical and pre-historical land management options. A synthesis of information conditions is essential for evaluating land manage- on landscape form, function, and history, as well as ment options. Another motivation for examining dis- current watershed and ecosystem conditions provides turbance history is that it provides the information the basis for identifying areas of the landscape and necessary to infer causes of current conditions. It components of the ecosystem sensitive to future would be difficult to understand the current condition changes. It also requires identifying potential of some stream channels, for example, without know- responses to land management activities. This may ing the history of log drives, salvage, and stream involve extrapolating current trends over longer time cleanup operations conducted during the past century periods and incorporating other factors (e.g., climate) (e.g., Sedell and Froggatt, 1984; Sedell et al., 1991). that may change over the same time period (Swanson et al., 1992). Watershed analysis defines the range of potential future conditions in a watershed, which What are Current Conditions? enables identifying desired future conditions and the steps necessary to attain them. The current condition of a watershed provides a snapshot in time of its state, which can be thought of as a collection of attributes that define key system properties (Brooks and Grant, 1992). This includes, HOW DO YOU DO IT? for example, the spatial distribution of vegetation age and community composition, current land The complex problem of analyzing a watershed use patterns, species distributions, and physical requires a relatively simple model of watershed
375 WATER RESOURCES BULLETIN Montgomery, Grant, and Sullivan processes and organization. A useful model is based stratification that helps formulate hypotheses about on the fundamental differences in form, function, and landscape processes and serves to guide subsequent ecosystem processes between hillslopes and channels. data collection. While no single classification scheme At this general level, a distinction can be drawn is applicable across modules and from one landscape between terrestrial and riparian vegetation and ter- to another, there are certain scales and attributes restrial and aquatic wildlife that are associated with that provide a logical foundation for organizing the hillslopes and channels, respectively. Watershed anal- stratification of each module (Table 2). A number of ysis is organized around a series of process/condition classification systems for some landscape elements modules (WFPB, 1992) that reflect this basic frame- have been proposed; there are several channel classi- work (Table 2). The impacts associated with roads can fication schemes, for example, that could provide an be examined in an independent module because they initial stratification (e.g., Rosgen, 1985; Paustian et include effects on erosional and hydrological processes al., 1992; Montgomery and Buffington, 1993; Whiting that affect both channels and hillslopes. and Bradley, 1993). Other systems exist for classify- While analysis modules address different processes ing vegetation associations (e.g., Franklin and Dyr- and resources, they all follow the same basic struc- ness, 1986). Developing such stratifications is ture and flow of logic. This sequence parallels the flow probably best pursued on a regional basis, since they of logic for the analysis as a whole (Figure 2). In each provide a set of default hypotheses or expectations component, critical issues are identified and the scope against which to evaluate conditions examined in the of inquiry is focused on answering a series of ques- field. This provides a guide for developing analyses tions; the watershed is stratified into landscape units and allows flexibility for analyzing different land hypothesized to be dominated by different processes; forms and contexts within a watershed. Imposing an and field observations and data are collected to docu- initial landscape stratification also precludes applying ment the history and condition of resources within the uniform assumptions about environmental conditions watershed (WFPB, 1992). This information is used to and processes throughout a landscape. revise the classification into landscape units that reflect both dominant processes and conditions, which are then used to interpret sensitivity to proposed Data Collection management activities. Finally, maps of landscape units defined from each of the modules are synthe- Collection of historical and contemporary data sized to generate a unified landscape stratification allows testing and refining hypotheses concerning that provides the basis for developing management geomorphological and ecological function embedded in prescriptions specific to individual landscape units. the initial landscape stratification. Such data also defines trends in watershed conditions and allows Define Critical Issues interpretation of current conditions within the context of historical disturbance regimes. Historical analyses often are limited by a paucity of available data; in At the outset of analysis for any particular water- many cases the available information is limited to shed, there is likely to be a set of critical issues recog- aerial photographs, land management histories, nized as of primary importance (e.g., declining salmon streamflow records, and previous inventories and stocks or grazing in riparian zones). While it is essen- monitoring data. Although opportunities for historical tial to address these issues during the analysis, it is analyses may be fairly restricted, even limited infor- imperative that they do not define the entire scope of mation on historical conditions can be extremely valu- the analysis. Otherwise, issues not initially recog- able for interpreting the influence of past land nized as important may be overlooked. Critical issues management on disturbance regimes and ecological help determine priorities in interpreting sensitivity systems. and can override other considerations in the develop- The potential to generate information on current ment of management prescriptions during subsequent conditions, on the other hand, is virtually unlimited. planning. Data collected in the analysis modules therefore must be directed towards assessment of conditions and landscape characteristics that are sensitive to Landscape stratification changes in the dominant ecological processes or dis- turbance regimes. These include characterization of Landscape stratification provides a means of orga- organism and habitat distributions and conditions, as nizing the landscape into discrete structural and func- well as linkages among processes (e.g., sediment sup- tional units. Each analysis module involves an initial ply to a channel, hydrologic connection of road and channel networks). WATER RESOURCES BULLETIN 376 TABLE 2. Examples of Steps in Watershed Analysis in Relation to Analysis Modules.
Hillslopes Mass Movements Wildlife and Surface Vegetation Aquatic Erosion Hydrology Channels Terrestrial Riparian Terrestrial (fish) Roads
Stratification • Geology Dominant hydrologic Valley segment Geoclimatic Dominant Habitat Habitat Road location Soils process (rain, snow,- types zone disturbance associations associations (ridge, midslope, Slope rain-on-snow) based on: Reach types Elevation regimes: (based on Stream size valley) Drainage area Elevation GradienU Debris flow vegetation, Stream Road type Geometry (convergent, Aspect confinement Flooding other) gradient (paved, gravel, divergent, planar) Soil depth/water Channel migration; Reach type skid) Stability models holding capacity evulsion Road age Bedrock conductivity Snow avalanche
Data Landslide/debris Stream flow changes Inventory of Fire history Riparian canopy Inventory of Inventory of Historical pattern Collection: flow inventory by (historical stream gage channel changes Blowdown condition changes habitat changes habitat changes and rates of road Historical classification strata records) in relation to through time history with time (aerial through time through time development plus land use land use, other strata (aerial photos) Vegetation photo) (aerial photos) (aerial photos; through time (aerial photos) pattern Historical old field surveys) Sediment production changes over population Historical and delivery rates to time including census data population census channels land use data (aerial photos)
Data Inventory/sampling of Location of channel Assessment of Age/seral stage Age/seral stage Current census Current census Road condition Collection: current processes heads; springs, seeps channel condition Species Species data data Percent road Current (gullies, surface erosion, and morphology composition composition Current habitat Current habitat length inte- etc.); field estimates of Structure Structure (open, condition and condition and grated with current sediment (stand density) closed canopy) distribution distribution stream network production Field estimate of road sediment production
Reclassification/ Mass movement and Potential for contributing Map of potential Map of potential Map of potential Map of habitat Map of potential Map of road/ Map Unit erosion hazard map to high and low flows for channel change vegetation pattern riparian vegetation potential based habitat utilization, channel network Delineation based on initial based on stratification, by reach type for and structure pattern based on on vegetation, based on riparian integration and stratification, historical landuse history, historical changes in land use, based on hillslope hillslope and riparian historical use vegetation, chan- extension and current condition data hydrology, mass disturbance disturbance regimes, patterns, and nel conditions, movement potential regime, land use land use, channel current and historical history change potential conditions use patterns
Montgomery, Grant, and Sullivan Questions Watershed analysis component
How does this Landscape classification based landscape work? on structure and processes
What has its history Data collection to discern historical been? conditions, trends
What is its current Data collection to assess current condition; legacy of past condition? disturbances
What are possible/desirable future Reclassification, scenario states for this landscape? generation, and synthesis Watershed Analysis How do we manage it so Development of prescriptions for as to achieve our objectives? redefined landscape units
Figure 2. Linkage Between Overriding Questions and Analysis Procedures Conducted Within Each Module.
Analysis of the current state or condition of a land- potential conditions of the biological systems inhabit- scape should allow analysts to answer critical ques- ing the watershed. tions with specific information as follows: What are the dominant disturbance regimes in this landscape? How are they distributed spatially? How frequently Landscape Unit Delineation do they occur and what impacts do they have on ecosystems? What are trends in hilislope and channel A primary product of each analysis module is delin- conditions, and how tightly coupled are these trends eation of landscape units defining areas within a to each other and land management activity within watershed that are dominated by different processes, the basin? How are wood, water, and sediment deliv- history, conditions, and sensitivities (i.e., response ered to and routed through the stream channels? How potential). Landscape unit boundaries can differ are terrestrial and aquatic species distributed among analysis modules because the factors and pro- through the watershed, and what are the dominant cesses examined in each analysis module differ. Addi- controls on their distribution and abundance? Such tionally, landscape units may be organized around information allows development of a watershed-spe- individual sub-basins within the larger watershed. cific model both for the processes creating, modifying, Landscape units developed in the channel module and destroying habitat and for the past, current, and might include: (1) debris-flow dominated headwater
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Watershed Analysis as a Framework for Implementing Ecosystem Management channels in portions of the watershed without evi- the example, we distinguish between channels and dence of recent disturbance; (2) headwater channels associated riparian zones that have and have not disturbed by landsliding; (3) low-gradient channels been recently disturbed. Similarly, lower-gradient with abundant large woody debris and little evidence areas of the watershed with little evidence for histori- of historical change; and (4) low-gradient channels cal impacts on channel conditions are combined into a with evidence of historical channel widening (Figure single landscape unit, as are steeper areas with more 3A). Landscape units defined in the mass wasting frequent fires. A data-rich narrative that is developed module may delineate, for example, areas where: for each of the final landscape units should describe (1) shallow landsliding is a major geomorphic process both the basis for identification of the unit and an but there is little evidence for historical changes in assessment of its potential response to different types landslide frequency; (2) widespread landsliding fol- of land management. This information provides the lowed road construction and timber harvest; (3) deep- basis for interpreting potential future conditions seated landsliding is a major process; and (4) surface within each landscape unit and developing an assess- and gully erosion are the major processes potentially ment of the potential trade-offs between management influenced management (Figure 3B). A map defining opportunities and potential future conditions. dominant disturbance regimes for vegetation may include units where fire, windstorms, debris flows, floods, or snow avalanches, each with different return periods, are the primary controls on stand structure LINKING WATERSHED ANALYSIS and age (Figure 3C). The information generated at TO PLANNING finer scales is tied to specific places and will be used in subsequent syntheses; the unit delineation maps Watershed analysis produces information, knowl- simply provide the spatial context for addressing edge, and understanding necessary for scientific management options at scales larger than individual interpretation to support informed decision-making, projects. but it is not equivalent to making management deci- The information generated during these analyses sions. Determining the activity appropriate for a provides a process- and landscape-specific framework watershed rests on weighing potential future condi- for assessing the capacity of a landscape to sustain a tions against planning objectives, legal mandates, and particular style of land use. Linkages and relations management constraints. Watershed analysis mod- among landscape attributes (e.g., hillslopes, channels, ules do not determine which management options and fish communities), however, need to be synthe- should be implemented; rather, they are designed to sized from the information gathered by the analysis provide the information necessary to make an modules. informed choice. Planning is the forum within which management options are identified and developed based on coupling knowledge with objectives. Synthesis Successfully implementing ecosystem or watershed management as a means for preserving ecosystem Synthesis is a phase of watershed analysis during integrity requires recognizing and considering not which results from the analysis modules are com- only physical and biological processes but also the bined into a watershed-level assessment of conditions social context within which decisions will be made and linkages among physical and biological resources and managed [see Lee (1992), Ludwig (1993), and (WFPB, 1993). Process linkages between hillslopes Stern (1993) for further discussion]. This involves and channels, for example, are examined and related both local contexts and larger regional and global con- to the condition and history of other resources. Hack texts that influence decision making [see also Blaikie and Goodlett s (1960) classic paper on the relation (1985) and Knuth and Nielsen (1991)]. While this between geomorphology and forest ecology provides a paper does not focus on these issues, a key to success- superb example of such a synthesis. This exercise fully bridging watershed analysis and planning may identify further information needs or reveal pre- involves assuring public participation and/or input in viously unrecognized relationships. Based on this syn- both analysis and subsequent decision making. This thesis, the watershed is reclassified into a final set of should foster an atmosphere of cooperation but will landscape units. These revised units serve as the not guarantee conflict resolution, especially among basis for developing management prescriptions, iden- parties with fundamentally incompatible objectives. tifying both potential and desired conditions, and Nonetheless, watershed analysis provides a manage- developing monitoring programs. able and logical framework for organizing stakeholder An example of this process involves reorganization input and coupling local public input with larger-scale and generalization of landscape units (Figure 4A). In interests and issues. Involvement of all interested
379 WATER RESOURCES BULLETIN Montgomery, Grant, and Sullivan
A
Headwater channels recently disturbed by landsliding and debris flows Debris flow-dominated headwater channels without Shallow landslide-prone evidence of recent disturbance areas not accelerated by timber harvest Low gradient channels with abundant coarse woody debris Shallow landslide prone areas accelerated by timber Low gradient channels lacking harvest ■ coarse woody debris 111 Areas underlain by Low gradient channels with deep-seated earthflows III evidence of channel widening Areas potentially subject III to surface and gully erosion
Open canopy deciduous reset by frequent debris flows (20 year return period) Closed canopy mixed deciduous and conifer reset by infrequent debris flows (200 year return period) Closed canopy conifer subject to bank erosion during infrequent floods IIII Open meadows and conifer patches due to snow avalanche and rockfalls Open canopy deciduous due ■ to frequent fluvial disturbance Moderately frequent stand- replacement fires (100-year return period) Infrequent stand replacement fires and windthrow (200-year return period)
Figure 3. Hypothetical Example of Landscape Units Developed in the (A) Channel, (B) Mass Wasting/Surface Erosion, and (C) Vegetation Disturbance Modules.