North Platte River Basin Wetland Profile and Condition Assessment March 31, 2012 Colorado Natural Heritage Program Colorado State University Fort Collins, CO 80523 North Platte River Basin Wetland Profile and Condition Assessment Prepared for: Colorado Parks and Wildlife Wetland Wildlife Conservation Program 317 West Prospect Fort Collins, CO 80526 U.S. Environmental Protection Agency, Region 8 1595 Wynkoop Street Denver, CO 80202 Prepared by: Joanna Lemly and Laurie Gilligan Colorado Natural Heritage Program Warner College of Natural Resources Colorado State University Fort Collins, Colorado 80523 In collaboration with Brian Sullivan, Grant Wilcox, and Jon Runge Colorado Parks and Wildlife Dr. Jennifer Hoeting and Erin Schliep Department of Statistics, Colorado State University Cover photographs: All photos taken by Colorado Natural Heritage Program Staff. Copyright © 2012 Colorado State University Colorado Natural Heritage Program All Rights Reserved i EXECUTIVE SUMMARY The North Platte River Basin covers >2,000 square miles in north central Colorado and is known for extensive wetland resources. Of particular importance to Colorado Parks and Wildlife (CPW), the basin’s wetlands serve as significant waterfowl breeding areas and refuge for rare amphibians, fish, and invertebrates. Recognizing the need for better information about wetlands across the state, CPW and Colorado Natural Heritage Program (CNHP) began a collaborative effort called Statewide Strategies for Colorado Wetlands to catalogue the location, type, and condition of Colorado’s wetlands through a series of river basin-scale wetland profile and condition assessment projects. This report summarizes finding from the second basinwide wetland condition assessment, conducted in the North Platte River Basin. The initial step in each project is to compile a “wetland profile” based on digital wetland mapping. Wetland profiles summarize the types, abundance, and distribution of wetlands among ecoregions and landownership within a given geographic area and can be used to establish baseline conditions, assess cumulative impacts, and inform conservation planning. The second step in each project is to conduct a field-based assessment of ecological condition and associated stressors that can be extrapolated to all wetland area in the basin. Assessing the ecological condition of wetlands within each basin provides a coarse filter for prioritizing on-the-ground efforts to protect and restore wetland habitat. Through this project, CPW and CNHP developed a wetland profile of the North Platte River Basin to document the spatial distribution of wetlands, conducted a field-based assessment of wetland condition, and used the data to estimate both overall condition of wetlands and the availability of wetland habitat across the basin. At the outset of this project, digital wetland mapping from U.S. Fish and Wildlife Service (USFWS)’s National Wetland Inventory (NWI) program was available for less than 10% of the basin, though paper maps drawn between the late 1970s and early 1980s existed for the entire area. To create the wetland profile, original paper maps for all topographic quads lacking digital spatial data were scanned and converted to geo-rectified digital polygons, producing a wall-to-wall map of wetlands in the basin. The digital NWI polygons were used to summarize wetland acreage in a number of different ways. To assess the condition of wetlands in the basin, 95 randomly selected wetland sites were visited in the field and surveyed following detailed protocols that addressed: 1) Landscape Context, 2) Biotic Condition, 3) Hydrologic Condition, and 4) Physiochemical Condition. Sites on actively managed hay pastures were removed from the sample pool to focus on natural and naturalized wetlands. Scores were produced for each site visited and summarized by wetland type and by geographic region across the basin. Site scores were extrapolated to estimate wetland condition of all non-irrigated wetland acres. A predictive model of wetland condition was also developed to predict the condition of wetlands not visited in the field. Based on digital NWI mapping, there are 138,043 acres of wetlands and water bodies within the basin, representing approximately 11% of the total land area. Lakes and rivers comprise 6,402 of the total NWI acres. The majority (73%) of the NWI mapped acres are freshwater herbaceous wetlands. When lakes and rivers are excluded, herbaceous wetlands make up 77% of wetland acres. Shrub wetlands are the second most common class, making up 19% of all NWI acres and 20% of wetland acres. Within the basin as a whole, 59% of wetland acres are irrigated and these acres are ii overwhelmingly (96%) freshwater herbaceous wetlands. Among all herbaceous wetlands, 75% are irrigated. In many cases, these irrigated wetlands are actively managed as hayfields and harvested during most years. When broken down by major landowner, 73% of wetland acres are privately owned. Private landowners hold a relatively greater share of wetland acres than they do of total area within the basin (33%). This is largely because the density of wetland acres is greater within the central North Park valley, where private landownership is concentrated, than in the publically owned mountain areas. Private landowners in North Park are more likely to be irrigating hay pastures, which can increase wetland acreage. Over 70% of privately owned wetland acres are irrigated, making up 91% of the total irrigated wetland acreage. For the purpose of understanding the quantity of habitat available to dabbling ducks in the basin, nine important habitat types were identified by CPW wildlife biologists. A crosswalk between the habitat types and NWI codes was developed, allowing for all mapped wetlands to be summarized by these habitat types. The most common habitat type identified in the basin is irrigated hay meadows, making up 53% of all NWI acres. This is slightly lower than all NWI acres mapped as irrigated (57%) because it does not include irrigated shrublands along the margins of hay meadows. After irrigated hay meadows, seasonal emergent wetlands and riparian areas without beaver influence both comprise 13% of all NWI acres. Beaver ponds and other beaver influenced wetlands make up another 4% of all NWI acres, as do lakes and reservoirs. All other habitat types identified as important for dabbling ducks make up < 1% of all NWI acres. A statewide Level 1 GIS-based Landscape Integrity Model (LIM) for wetlands was applied to the North Platte River Basin. Results from the LIM show that although only 10% of total basin area falls within the severe stress category, 27% of wetland acres fall within the severe stress category and an additional 50% fall within the high stress category. This is largely due to the distribution of wetland acres, which are more concentrated on the valley floor and therefore affected by roads and development, agriculture, and hydrologic modification. Though these results indicate high stress in the basin, the LIM is not yet fully calibrated and over predicts high stress when compared to field- based scores of wetland condition. Among the 95 randomly selected sites, riparian shrublands were the most common wetland type encountered with 46 sites, making up 48% of all sites surveyed, and were broadly distributed across the basin. Wet meadows were the second most common type with 28 sites surveyed. In addition, the sampled wetlands included 13 fens, 5 marshes, 2 riparian woodlands, and 1 alkaline basin. Each wetland type had its own distinct suite of plant species. Within surveyed wetlands, 612 individual plant taxa were encountered, including 538 species were identified to the species level. This represents ~17% of the entire Colorado flora. Condition of sampled sites was assessed using the Floristic Quality Assessment (FQA or Mean C), Ecological Integrity Assessment (EIA), and Vegetation Index of Biotic Integrity (VIBI) methods. Mean C values for sampled sites ranged from 2.77–7.08 and the range of Mean C scores was related to both wetland type and the geographic gradient. The lowest Mean C scores and largest variation in scores occurred below 8500 ft. Above 9000 ft., sites predictably showed high Mean C scores. Not surprisingly, wetlands characteristic of higher elevations had the highest average Mean C values, while wetlands more common at lower elevations had lower average Mean C values. For overall EIA iii scores, 43 of the wetlands sampled were A-ranked, 40 were B-ranked, and 12 were C-ranked. No wetland was ranked D, where wetland conditions and their associated functions are considered significantly compromised and unlikely to be restorable. Extrapolated results indicate that 34% of all wetland area in the basin would receive an overall EIA rank of A, 48% would receive a B, and 17% would receive a C. Across all methods, trends clearly indicate that wetlands in the North Platte River Basin are in very good condition. The lack of D-ranked wetlands and low proportion of Cs indicate the basin contains many healthy, intact wetlands. The landscape of the basin is less fragmented than other parts of the state and wetlands generally have good buffers. Localized hydrologic modifications are evident, but few wetlands had signs of severe hydrologic alteration that would significantly threaten wetland health. There is little substrate disturbance and no obvious visual signs of water quality impairment. Very few noxious weeds were observed in the wetlands, though Canada thistle was found in a handful of sites. Several sites in North Park had high cover of non-native pasture grasses because they were former hay fields or were adjacent to hay fields, but many wetlands had very high Mean C and EIA biotic scores, indicative of thriving, diverse native plant communities. Grazing by livestock and browse by native ungulates were the most common stressors observed within North Platte wetlands, which is consistent with the dominant land use in the basin. However, grazing impacts were rarely considered severe in the sampled wetlands. Continuing best management practices for cattle, such as fencing off stream channels and rotating grazing, will maintain the current balance between cattle ranching and healthy wetland systems. Oil and gas wells were not observed within this study, but drilling in the basin has increased even since 2010 and could potentially lead to significant impacts in coming years. The field methods used in this study do not address habitat quality for specific wildlife species, but can be reflect overall condition. Through this project, eight habitat features were identified as important for dabbling ducks, but these were not developed in time to use in the assessment of wetland condition. However, though concurrent field studies conducted by CPW, two of the eight habitat value factors identified as important to dabbling ducks (vegetation type and residual cover depth) were evaluated and shown to influence duck production. Of the 138,043 acres of wetlands and water bodies mapped in the North Platte River Basin, 90% (124,350 acres) was identified as types important to waterfowl. This justifies continued emphasis on wetland conservation in this basin by CPW and partner agencies and organizations with shared missions to conserve wetland-dependent wildlife. The prevalence of irrigated hay meadows (54% of all NWI mapped acres) in relation to other wetland types warrants new field studies to determine the importance of this habitat to wildlife. Other habitat types represent far fewer acres, and could be selectively managed for. iv SIGNIFICANT FINDINGS Wetland quantity and types • There are 138,043 acres of wetlands and waterbodies in the North Platte River Basin (131,642 acres without lakes and rivers). • Wetlands and waterbodies represent 10% of the basin. • Herbaceous wetlands represent 77% of all wetlands, of which 75% are mapped as irrigated. • 60% of all wetlands (>78,000 acres) are mapped as irrigated. These are primarily managed for hay production, though some are managed for wildlife habitat. • 32,000 additional acres are mapped as irrigated land but not as wetland and may represent newly irrigated lands since the wetlands were mapped. • Beaver-influenced wetlands comprise 4% of all mapped wetland acres. Wetland distribution within basin • 69% of wetlands and water bodies are in the North Park valley (Sagebrush Parks ecoregion). • Higher elevations contain short stature shrublands, beaver-influenced riparian corridors, kettle ponds, fens, and alpine wet meadows. • Lower elevations contain extensive tall stature riparian wetlands, natural wet meadows, alkaline basins, and marsh vegetation along lakeshores and ponds. • Beaver-influenced wetlands are concentrated in mid-elevation and subalpine zones; and are scare in the alpine zone, North Park, and the Laramie Basin. Ownership of wetland acres • 73% of wetland acres are privately owned. • 15% are owned by the U.S. Forest Service • 5% are owned by the U.S. Fish and Wildlife Service • 4% are owned by the U.S. Bureau of Land Management • 3% are owned by the Colorado State Land Board • 1% are owned by Colorado Parks and Wildlife Wetland Condition • Population level estimates indicate that 82% (44,409 acres) of non-irrigated wetlands are A- or B-ranked based on Level 2 EIA scores, meaning they are in reference condition or deviate only slightly from reference condition. • An additional 17% (9,096 acres) are C-ranked, meaning a moderate deviation from reference condition that would warrant some type of management or restoration. • Few wetlands had signs of severe hydrologic alteration that would significantly threaten wetland health. • There is little substrate disturbance and no obvious visual signs of water quality impairment. • Biotic condition is generally high. Very few noxious weeds were observed, though wetlands that were former hay fields or adjacent to active hay field contained significant cover on non-native species. Stresses faced by wetlands • Higher stress wetlands are located in the valleys where human activities have altered the landscape. v • Lower stress wetlands occur at higher elevations where there is less human-caused disturbance. • Grazing by livestock and browsing by native ungulates were the most common stressors observed. However, grazing impacts observed in the field were rarely considered severe. Waterfowl value • 90% of wetland acres (124,350 acres) are of types important to waterfowl, and a large majority of this is irrigated hay meadows. • Eight habitat features were identified as potentially important to waterfowl: (1) dominant vegetation type, (2) percent of emergent cover, (3) depth of residual cover, (4) interspersion (ratio of cover to water), (5) size of wetland, (6) landscape context (percent of wetlands or open water on the landscape within a defined buffer of wetland margins or habitat edge), (7) stream flow (cubic feet per second), and (8) stream order. • Empirical data from field studies confirmed that vegetation type and residual cover did influence duck production, with higher production in sites dominated by bulrush and with increasing depth of residual cover. vi ACKNOWLEDGEMENTS The authors at Colorado Natural Heritage Program (CNHP) would like to acknowledge the U.S. Environmental Protection Agency (EPA) Region 8 and Colorado Parks and Wildlife (CPW)’s Wetlands Program for their financial support and encouragement of this project. Special recognition goes to Jill Minter, former EPA Region 8 Wetland Monitoring and Assessment Coordinator, for her support for Colorado’s growing wetland assessment program. Brian Sullivan, CPW Wetlands Program Coordinator; Grant Wilcox, CPW GIS Analysts; and Jon Runge, CPW Avian Researcher, all contributed time and energy to this project and recruited the help of other experts within their agency. Kevin Bon, Bruce Droster, and Jane Harner from U.S. Fish and Wildlife Services (USFWS)’s National Wetland Inventory (NWI) Program have been incredibly helpful over the years as we grow our capacity to map wetlands in Colorado. Zack Reams, former GIS Analyst with both CPW and CNHP, deserves particular recognition as the first Wetland Mapping Specialist we hired. The digital polygons of North Platte wetlands are all his work. Special thanks to CNHP’s Michelle Fink, who developed the Wetlands Landscape Integrity Model (LIM) and also the Wetland Condition Assessment Database. Her knowledge and skills have been integral to our analyses. Thanks also to John Sanderson and Jan Koenig of The Nature Conservancy (TNC) for sharing their time, expertise and data through the Freshwater Measures of Conservation Success dataset that is used in both the Wetland LIM and to double check our field-based measures. And a huge thanks to Dr. Jennifer Hoeting and Ph.D. Candidate Erin Schliep who worked closely with us on statistical analyses. In additional to the analyses presented in this report, Erin and Dr. Hoeting have been able to use CNHP condition assessment data in their own work to advance the understanding of on the ground condition scores and landscape level predictors. We extend much gratitude to CNHP field technicians Lauren Alleman, Erick Carlson, Conor Flynn, Nina Hill, Jenny Howard, Anne Maurer, and Eric Scott for their hard work collecting data. Thanks to botanists extraordinaire Pam Smith of CNHP and Jennifer Ackerfield of the CSU Herbarium for help with plant identification. CNHP Wetland Ecology Data Technician Ellen Heath was invaluable for entering and QC’ing pages and pages of field data. The project could not have happened without the support and assistance of local partners in the North Platte River Basin. Barbara Vasquez, chair of the North Park Wetland Focus Area Committee (FAC), was instrumental in helping with logistics and making important connections with others in the basin. Thanks also go to agency biologists and land managers who let us survey on their lands, including Ann Timberman and Mead Klavetter of USFWS; Liz Schnackenberg, Rick Henderson, Marti Aiken, and Mark Westfall of the Medicine Bow-Routt National Forest; Steve Popovich of the Arapaho-Roosevelt National Forest; Paula Belcher of the BLM; Liza Rossi, Josh Dilley, and Zack Sanders of CPW; David Rodenberg and Lane Osborn of the State Land Board; Brook Lee and Kent Minor of State Forest State Park. And a very special thanks to the private landowners who allowed us onto their lands. During the course of this project, we gained tremendous technical assistance, ideas and overall guidance from our colleagues at CNHP, especially Dave Anderson, Denise Culver, Karin Decker, Amy vii Lavender, Renee Rondeau, Gabrielle Smith, and Joe Stevens. Colleagues at the Montana Natural Heritage Program (MTNHP) have been equally important in guiding the ideas of our work in both wetland mapping and wetland condition assessment. Special thanks go to Meghan Burns, Cat McIntyre, Karen Newlon, and Linda Vance. Finally, we would like to thank Paula Nicholas with the CPWand Mary Olivas and Carmen Morales with Colorado State University for logistical support and grant administration. viii TABLE OF CONTENTS EXECUTIVE SUMMARY ......................................................................................... I SIGNIFICANT FINDINGS ..................................................................................... IV ACKNOWLEDGEMENTS ..................................................................................... VI TABLE OF CONTENTS ....................................................................................... VIII LIST OF APPENDICES ........................................................................................... X LIST OF TABLES .................................................................................................. XI LIST OF FIGURES ............................................................................................... XIII 1.0 INTRODUCTION ............................................................................................. 1 1.1 Statewide Strategies for Colorado Wetlands ....................................................................... 1 1.2 Project Objectives ................................................................................................................. 3 1.3 Wetland Monitoring and Assessment Frameworks ............................................................. 5 1.3.1 EPA’s Level 1-2-3 Framework for Wetland Assessment ................................................. 5 1.3.2 NatureServe’s Ecological Integrity Assessment Framework .......................................... 6 1.4 Previous Wetland Studies in North Platte River Basin ......................................................... 6 2.0 STUDY AREA .................................................................................................. 9 2.1 Geography ............................................................................................................................. 9 2.2 Ecoregions and Vegetation ................................................................................................. 10 2.3 Geology ............................................................................................................................... 14 2.4 Climate and Hydrology ........................................................................................................ 15 2.5 Land Ownership and Land Use ........................................................................................... 15 3.0 METHODS ................................................................................................... 18 3.1 Wetland Profile and Landscape Integrity Model ................................................................ 18 3.2 Survey Design and Site Selection ........................................................................................ 18 3.2.1 Target Population ........................................................................................................ 18 3.2.2 Subpopulations/Classification ...................................................................................... 19 3.2.3 Sample Size .................................................................................................................. 20 3.2.4 Sample Frame .............................................................................................................. 20 3.2.5 Selection Criteria .......................................................................................................... 20 3.3 Field Methods ..................................................................................................................... 22 3.3.1 Defining the Wetland Assessment Area (AA) ............................................................... 22 3.3.2 Classification and Description of the AA ...................................................................... 23 3.4.3 Ecological Integrity Assessment and the Human Disturbance Index ........................... 24 3.3.4 Vegetation Data Collection .......................................................................................... 26 4.3.5 Soil Profile Descriptions and Groundwater Chemistry ................................................. 27 3.4 Data Management .............................................................................................................. 28 3.5 Data Analysis ....................................................................................................................... 28 3.5.1 Characterization of Wetland Vegetation ..................................................................... 28 3.5.2 FQA and EIA Analysis ................................................................................................... 29 3.5.3 VIBI Analysis ................................................................................................................. 30 3.5.4 Empirical Model of Wetland Ecological Integrity ........................................................ 30 3.6 Evaluation of Waterfowl Habitat ........................................................................................ 31 ix 4.0 RESULTS ...................................................................................................... 33 4.1 Wetland Profile and Landscape Integrity Model ................................................................ 33 4.1.1 Wetland Profile of the North Platte River Basin .......................................................... 33 4.1.2 Wetland Landscape Integrity Model ............................................................................ 42 4.2 Sampled Wetlands .............................................................................................................. 45 4.2.1 Implementation of the Survey Design .......................................................................... 45 4.2.2 Evaluation of Areas Mapped as Uplands and Irrigated Wetlands .............................. 48 4.2.3 Sampled Wetlands by Ecological System and HGM Class ........................................... 49 4.2.4 Sampled Wetlands by Landownership ......................................................................... 54 4.2.5 Population Estimates of Wetland Type ........................................................................ 55 4.3 Characterization of Wetland Vegetation ............................................................................ 55 4.3.1 Species Diversity in North Platte Wetlands .................................................................. 55 4.3.2 Relationships between Wetland Vegetation and Environmental Factors ................... 58 4.4 Floristic Quality Assessment ............................................................................................... 61 4.5 Ecological Integrity Assessment .......................................................................................... 67 4.5.1 EIA Scores of Sampled Wetlands .................................................................................. 67 4.5.2 Population Estimate of Wetland Condition ................................................................. 71 4.5.3 Land Use Stressors ....................................................................................................... 72 4.6 Vegetation Index of Biotic Integrity .................................................................................... 74 4.6.1 Wet Meadows .............................................................................................................. 74 4.6.2 Riparian Shrublands ..................................................................................................... 76 4.6.3 Fens .............................................................................................................................. 78 4.7 Empirical Model of Wetland Ecological Integrity ............................................................... 78 4.8 Evaluation of Waterfowl Habitat ........................................................................................ 81 5.0 DISCUSSION ................................................................................................ 82 5.1 Wetlands of the North Platte River Basin ........................................................................... 82 5.1.1 Irrigated Wetlands ....................................................................................................... 82 5.1.1 Non-Irrigated Wetlands ............................................................................................... 84 5.2 Ecological Condition of Wetlands in the North Platte River Basin ..................................... 84 5.3 Evaluation of Waterfowl Habitat ........................................................................................ 87 5.4 Management Implications .................................................................................................. 87 6.0 REFERENCES ................................................................................................ 88 x LIST OF APPENDICES APPENDIX A: Field Key to Wetland and Riparian Ecological Systems of Montana, Wyoming, Utah, and Colorado ............................................................................................................... 94 APPENDIX B: Field Key to Hydrogeomorphic Classes in the Rocky Mountains ............................ 99 APPENDIX C: NWI Codes Included in the North Platte River Basin Sample Frame .................... 100 APPENDIX D: North Platte River Basin Wetland Condition Assessment Field Forms and Example Field Maps ............................................................................................................ 104 APPENDIX E: Ecological Integrity Assessment (EIA) Metric Rating Criteria and Scoring Formulas for the North Platte River Basin .......................................................................................... 123 APPENDIX F: NMS Ordination Settings and Results.................................................................... 129 APPENDIX G: Habitat Quality for Dabbling Ducks in North Park, Colorado: Assessment, Monitoring Protocols, and Management Tools .................................................................. 132 APPENDIX H: Intermountain Duck Habitat Management Pilot Study, North Park .................... 156 APPENDIX I: Wetland Acres by Land Manager and Specific Management Unit within the North Platte River Basin ................................................................................................................ 168 APPENDIX J: Most Common Plant Species Encountered In the North Platte River Basin by Ecoregional Strata ............................................................................................................... 172 xi LIST OF TABLES Table 1. Definition of Ecological Integrity Assessment ratings. ...................................................... 7 Table 2. Level III and IV Ecoregions within the North Platte River Basin. .................................... 12 Table 3. Descriptions of Level IV Ecoregions within the North Platte River Basin. ...................... 12 Table 4. Wetland Ecological Systems found in the North Platte River Basin. .............................. 20 Table 5. Ecoregional strata and number of target sample points used in the North Platte River Basin survey design. .............................................................................................................. 21 Table 6. Final EIA metrics used for the North Platte River Basin. ................................................. 24 Table 7. HDI metrics and stressor categories. .............................................................................. 25 Table 8. Variables tested for inclusion in the empirical model of wetland condition. ................. 31 Table 9. Wetland acreage in the North Platte River Basin by NWI system / class. ...................... 34 Table 10. Wetland acreage in the North Platte River Basin by NWI hydrologic regime. ............. 34 Table 11. Wetland acreage in the North Platte River Basin by NWI modifier and extent irrigated.. ............................................................................................................................... 35 Table 12. Wetland acreage in the North Platte River Basin by grouped land owner and extent irrigated. ................................................................................................................................ 37 Table 13. Wetland acreage in the North Platte River Basin by ecoregion and NWI system / class. ............................................................................................................................................... 38 Table 14. Wetland acreage in the North Platte River Basin by ecoregion and NWI hydrologic regime. .................................................................................................................................. 40 Table 15. Wetland acreage in the North Platte River Basin by ecoregion, grouped land owner and extent irrigated. ............................................................................................................. 41 Table 16. Wetland acreage in the North Platte River Basin by habitat types considered important and less important for dabbling ducks. ............................................................... 42 Table 17. Wetland LIM stressor class for wetlands by ecoregion. ............................................... 43 Table 18. Wetland LIM stressor class for wetlands by major wetland type. ................................ 44 Table 19. Wetland LIM stressor class for wetlands by major landowner. ................................... 45 Table 20. Number of wetland points evaluated, skipped, and surveyed by ecoregional strata. . 47 Table 21. Rejection cause for all points evaluated but not surveyed. ......................................... 47 Table 22. Sampled wetlands by ecoregional strata and Ecological System. ................................ 49 Table 23. Sampled wetlands by ecoregional strata and HGM class. ............................................ 54 Table 24. Sampled wetlands by ecoregional strata and major land owner. ................................ 54 Table 25. Sampled wetlands by Ecological System and major land owner. ................................. 55 Table 26. Ten most common plant species encountered in North Platte River Basin wetlands. 57 Table 27. Reference table for species codes in Figure 26. ........................................................... 59 Table 28. Means and standard deviations of all FQA metrics by Ecological Systems. ................. 66 Table 29. EIA ranks by ecoregional strata. .................................................................................... 68 Table 30. EIA ranks by Ecological Systems. ................................................................................... 69 Table 31. Component EIA ranks by Ecological Systems. ............................................................... 70 Table 32. Population estimate of wetland EIA ranks for the North Platte River Basin. ............... 72 Table 33. Anthropogenic land uses and natural disturbances observed in wetland assessment areas (AA). ............................................................................................................................. 73 xii Table 34. Anthropogenic land uses and natural disturbances observed in 500 m envelopes surrounding the AAs. ............................................................................................................ 74 Table 35. Selected variables included in the predictive model of wetland condition. ................ 78 Table 36. Fitted vs. actual EIA ranks. ............................................................................................ 78 Table 37. Model predicted EIA ranks vs. EIA ranks extrapolated from the survey design. .......... 79 xiii LIST OF FIGURES Figure 1. North Platte River Basin in Colorado (HUC 6: 1018000). ................................................. 3 Figure 2. HUC8 river subbasins, HUC12 watersheds, and major mountain ranges within the North Platte River Basin. ......................................................................................................... 9 Figure 3. Level III and IV Ecoregions within the North Platte River Basin. ................................... 11 Figure 4. Dominant geology of the North Platte River Basin........................................................ 14 Figure 5. Land ownership within the North Platte River Basin. .................................................... 16 Figure 6. Target wetland sample points drawn for the North Platte River Basin. ....................... 22 Figure 7. Example AA photos from the North Platte River Basin wetland condition assessment. ............................................................................................................................................... 24 Figure 8. Schematic of the 20 m x 50 m vegetation plot with a two by five array of ten 10 m x 10 m modules. ........................................................................................................................... 26 Figure 9. Digital NWI mapping in the North Platte River Basin, including extent of irrigated lands. ............................................................................................................................................... 33 Figure 10. Wetland acreage in the North Platte River Basin by ecoregion and NWI system / class. ............................................................................................................................................... 39 Figure 11. Comparison of Wetland LIM stressor classes for the entire North Platte River Basin (left) and all NWI acres within the basin (right). .................................................................. 43 Figure 12. Map of Wetland LIM stressor classes across the North Platte River Basin. ................ 44 Figure 13. Randomly selected wetlands sampled in the North Platte River Basin. ..................... 46 Figure 14. Comparison of land ownership distribution of the initial 95 target points evaluated and the 95 wetland points actually sampled after non-target and access-denied points were dropped from design ................................................................................................... 48 Figure 15. Sampled wetlands by ecoregional strata and Ecological System. ............................... 50 Figure 16. Photographs of high elevation riparian shrublands in the North Platte River Basin. . 51 Figure 17. Photographs of low elevation riparian shrublands in the North Platte River Basin.... 51 Figure 18. Photographs of wet meadow in the North Platte River Basin. ................................... 51 Figure 19. Photographs of fens in the North Platte River Basin. .................................................. 52 Figure 20. Photographs of low elevation marshes in the North Platte River Basin. .................... 52 Figure 21. Photographs of high elevation marshes in the North Platte River Basin. ................... 52 Figure 22. Photographs of riparian woodlands in the North Platte River Basin. ......................... 53 Figure 23. Photographs of the alkaline depression in the North Platte River Basin. ................... 53 Figure 24. Estimated distribution of Ecological Systems across non-irrigated wetland area in the North Platte River Basin. ....................................................................................................... 56 Figure 25. Estimated distribution of HGM classes across non-irrigated wetland area in the North Platte River Basin. ................................................................................................................. 56 Figure 26. NMS ordination of plots (shown as symbols grouped by Ecological System) in species space. .................................................................................................................................... 59 Figure 27. NMS ordination of plots (shown as symbols grouped by ecoregion) in species space. ............................................................................................................................................... 60 Figure 28. NMS ordination of plots (shown as symbols grouped by land owner) in species space. ............................................................................................................................................... 60 Figure 29. Frequency of Mean C values for all sampled wetlands. .............................................. 62 xiv Figure 30. Range of Mean C scores by ecoregional strata. .......................................................... 63 Figure 31. Range of Mean C scores by Ecological System. ........................................................... 63 Figure 32. Frequency of Mean C values for all sampled wet meadows. ...................................... 64 Figure 33. Frequency of Mean C values for all sampled riparian shrublands and woodlands. .... 64 Figure 34. Frequency of Mean C values for all sampled fens. ...................................................... 65 Figure 35. Frequency of Mean C values for all sampled marshes. ............................................... 65 Figure 36. EIA ranks by ecoregional strata. .................................................................................. 68 Figure 37. EIA ranks by Ecological Systems................................................................................... 69 Figure 38. Cumulative distribution function of overall EIA scores and ranks for wetlands in the North Platte River Basin. ....................................................................................................... 71 Figure 39. Estimated wetland acres in the North Platte River Basin ranked A, B, and C, along with irrigated acres. .............................................................................................................. 72 Figure 40. Frequency of estimated Wet Meadow VIBI scores for all wet meadows sampled with Level 3 protocols. .................................................................................................................. 75 Figure 41. Correlation of estimated Wet Meadow VIBI scores to the Human Disturbance Index. ............................................................................................................................................... 76 Figure 42. Frequency of estimated Riparian Shrubland VIBI scores for all riparian shrublands sampled with Level 3 protocols. ........................................................................................... 77 Figure 43. Correlation of estimated Riparian Shrubland VIBI scores to the Human Disturbance Index. ..................................................................................................................................... 77 Figure 44. Predicted EIA ranks at 7,830 randomly selected wetland points. ............................... 79 Figure 45. Observed EIA scores vs. predicted EIA scores and LIM values for all sampled wetlands. ............................................................................................................................... 80 1 1.0 INTRODUCTION Wetlands are an integral component of Colorado’s landscape. They provide a host of beneficial services, such as flood abatement, storm water retention, groundwater recharge, and water quality improvement (Mitsch & Gooselink 2007; Millennium Ecosystem Assessment 2005). Wetlands are particularly important for wildlife because they are highly productive and diverse ecosystems, providing habitat for many of Colorado’s species. Of the nearly 500 wildlife species in Colorado, more than 25% are considered “wetland-dependent,” meaning wetlands are their primary habitat (Ringelman 1996). Many others use wetlands and riparian areas at some point during their life cycle. The relative importance of wetlands is underscored by the fact that they occupy a small fraction of the landscape. Though total acreage of wetlands in Colorado is unknown, estimates place the extent at roughly 1 million acres or 1.5% of Colorado’s land area (Dahl 1990). Historically, Colorado likely supported twice the wetland acreage that exists today. Up to 50% of Colorado’s original wetlands have been drained and converted to farmland or urban development or lost as a result of water diversion and storage. Wetlands in Colorado continue to be impacted by multiple human uses, but the magnitude of these impacts is difficult to quantify as data on the location, type, and condition of Colorado’s wetlands are limited. To ensure the benefits Coloradoans receive from wetlands continue into the future, scientifically grounded information about the status and trends of Colorado’s wetland resource is essential for wetland conservation and management. 1.1 Statewide Strategies for Colorado Wetlands Recognizing the need for better information, Colorado Parks and Wildlife (CPW) and the Colorado Natural Heritage Program (CNHP) began a collaborative effort called Statewide Strategies for Colorado Wetlands to catalogue the location, type, and condition of Colorado’s wetlands through a series of river basin-scale wetland profile and condition assessment projects (Lemly et al. 2011). The first project was a pilot assessment of the Rio Grande Headwaters River Basin (Lemly et al. 2011). This report from the North Platte River Basin represents the second. CPW and CNHP plan to implement a rotating basin strategy for wetland assessments, beginning a new river basin study every one to two years depending on resource availability. The mission of CPW’s Wetland Wildlife Conservation Program1 is to maintain or improve the population status of priority wetland- dependent wildlife species, primarily through restoration of critical wetland habitats. Data from the wetland profile and condition assessment projects will help prioritize funding through the Wetlands Program and will feed directly into the program’s strategic plan (CPW 2011). The information can also be used by numerous other partners interested in the conservation and management of Colorado’s wetlands. The initial step in each project is to compile a “wetland profile” based on digital wetland mapping. Wetland profiles summarize the types, abundance, and distribution of wetlands within a given geographic area and can be used to establish baseline conditions, assess cumulative impacts, and 1 For more information on CPW’s Wetlands Program and to read the program’s strategic plan, see the website: (http://wildlife.state.co.us/LandWater/WetlandsProgram/). http://wildlife.state.co.us/LandWater/WetlandsProgram/ 2 inform strategic goals (Bedford 1996; Gwin et al. 1999; Johnson 2005). By connecting wetland habitat types within the profile with specific wildlife species, general statements can be made about the extent of wildlife habitat available. Depending on need or interest, other classification systems (e.g., Cowardin: Cowardin et al. 1979; Hydrogeomorphic: Brinson 1993; NatureServe’s Ecological Systems: Comer et al. 2003) can be used to evaluate different functions and services provided by a basin’s wetland resources. The second step in each project is to conduct a field-based assessment of ecological condition and associated stressors that can be extrapolated to all wetland area in the basin. As human stressors negatively impact wetland condition, the ability of a wetland to provide functions and services, such as wildlife habitat, may also be negatively impacted. Assessing the ecological condition of wetlands within each basin provides a coarse filter for prioritizing on-the-ground efforts to protect and restore wetland habitat. The link between general ecological condition and specific habitat quality is based on the assumption that a wetland in its natural, minimally impacted state will provide maximum suitable habitat for the wetland-dependent wildlife that use that wetland type. To confirm this connection, however, additional research is needed. Through this and subsequent wetland assessment projects, CPW and CNHP will seek to develop methods to assess specific habitat quality as well as general ecological condition. The North Platte River Basin (Figure 1) in north central Colorado has long been recognized for its wetland resources (USFWS 1955). Of particular importance to CPW, the basin’s wetlands serve as significant waterfowl breeding areas and refuge for rare amphibians, fish, and invertebrates. A recent study of important wetlands in the basin documented the area’s high biodiversity significance for both plant and animal populations (Culver et al. 2010). Wetland complexes in the basin support all three rare montane amphibians: boreal toad (Bufo boreas boreas), northern leopard frog (Rana pipiens), and wood frog (Rana sylvatica). The basin also contains one of three known Colorado breading sites for the American white pelican (Pelecanus erythrorhynchos), one of the few Colorado nesting populations of greater sandhill cranes (Grus canadensis tabida) and Colorado’s largest nesting populations of willets (Catoptrophorus semipalmatus). Presently, many of the basin’s large wetland complexes are still intact and contiguous, providing migration corridors and extensive wildlife habitat. However, effective management is needed to preserve this resource in the face of increasing human pressure. Demand from major urban areas for water development and storage projects, rapid growth in Colorado’s oil and gas industry, and significant changes in forest health threaten the long-term viability and integrity of the basin’s wetland resources. Through this project, CPW and CNHP developed a wetland profile of the North Platte River Basin to document the spatial distribution of wetlands, conducted a field-based assessment of wetland condition, and used the data to estimate both overall condition of wetlands and the availability of wetland habitat across the basin. 3 Figure 1. North Platte River Basin in Colorado (HUC 6: 1018000). The study area is bound by the 6-digit HUC river basin boundaries to the south, east, and west and the Colorado state line to the north. The basin encompasses all of Jackson County and a portion of western Larimer County. Blue lines show rivers, lakes, and reservoirs. Inset map shows study area in relation to Denver and all counties in the state. 1.2 Project Objectives The four primary objectives of this project were to (1) compile existing spatial data on wetlands in the North Platte River Basin and develop a wetland profile; (2) conduct a statistically valid, field- based survey of wetland condition in the basin; (3) model the distribution of wetland condition throughout the basin using collected field data and additional spatial data on potential stressors; and (4) determine metrics for measuring key habitat features for priority waterfowl species. The project objectives were implemented with the following tasks: 1. Compile existing spatial data on wetlands in the North Platte River Basin and develop a wetland profile. (Implemented by CPW and CNHP.) • Digital wetland mapping from the U.S. Fish and Wildlife Service (USFWS) National Wetland Inventory (NWI) program was compiled for the basin. 4 • Based on digital NWI mapping, a detailed wetland profile was developed summarizing the extent of wetland acreage throughout the basin by NWI system/class, hydrologic regime, extent modified, extent irrigated, land ownership, and Level IV Ecoregions. • Along with the wetland profile, a landscape level assessment of wetland condition within the basin was conducted based on a statewide Wetland Landscape Integrity Model. 2. Conduct a statistically valid field-based assessment of wetland condition for the North Platte River Basin. (Implemented by CNHP.) • Using the digital NWI mapping, a spatially balanced random sample survey design was developed for the North Platte River Basin based on principles outlined by U.S. Environmental Protection Agency (EPA)’s Environmental Monitoring and Assessment Program (Stevens and Olson 2004; Detenbeck et al. 2005). • The ecological condition of 95 randomly selected wetlands was measured using rapid and intensive protocols developed by CNHP. These protocols include the Floristic Quality Assessment (FQA: Rocchio 2007b), Ecological Integrity Assessment (EIA: Faber- Langendoen et al. 2008a; Lemly and Rocchio 2009a), and Vegetation Index of Biotic Integrity (VIBI: Rocchio 2007a; Lemly and Rocchio 2009b), all of which were developed for Colorado with funds provided by EPA Region 8 Wetland Program Development Grants and CPW’s Wetlands Program. • The proportion of wetland area within major condition classes was estimated based on field collected data. 3. Model the distribution of wetland condition throughout the basin using collected field data and additional spatial data on potential threats and stressors. (Implemented by CNHP through a partnership with the CSU Statistics Department.) • A regression model of wetland condition was developed in which the response was overall EIA scores and the predictors were spatial data on potential threats and stressors. • Wetland condition was predicted at 7830 random locations across the basin to provide a spatially explicit map of predicted condition. 4. Identify metrics for measuring key habitat features for priority waterfowl species. (Implemented by CPW.) • Literature on the specific wetland habitat needs of dabbling ducks was reviewed to determine key habitat features that can be easily and repeatedly measured in the field (i.e., hydrological regime, water depth, plant associations, open water interspersion, proximity of upland types, food sources, etc.). 5 • Specific habitat requirements of waterfowl were investigated in the field to determine how hydrologic regime and vegetation structure influence waterfowl populations. Field work combined hydrologic and vegetation measures with nest searching, marking of waterfowl with leg bands and nasal markers, and re-sighting of nasal-marked hens. 1.3 Wetland Monitoring and Assessment Frameworks To maximize the utility of the information, work conducted through this project can be viewed through two important frameworks. First is the EPA’s Level 1-2-3 Framework for wetland assessment, which defines an approach to wetland assessment at multiple scales of time, cost, and accuracy. The second is NatureServe’s Ecological Integrity Assessment Framework, which outlines an approach to assessing the condition of ecological resources, in this case wetlands. Both frameworks are discussed briefly below. 1.3.1 EPA’s Level 1-2-3 Framework for Wetland Assessment Acknowledging that it is impossible to visit every wetland across a landscape to determine the range of condition, EPA recommends a three tiered approach to wetland assessment. Within the Level 1-2-3 Framework2, Level 1 assessments are broad in geographic scope and used to characterize resources across an entire landscape. They generally rely on information available digitally in a GIS format or through remote sensing. Goals of Level 1 assessments may include summarizing the extent and distribution of a resource (such as wetland mapping from air photography) or modeling the condition of wetlands based on anthropogenic stressors such as roads, land use, resource extraction, etc. The wetland profile concept is essentially a Level 1 assessment. Level 1 assessments can be applied across a large area and can summarize general patterns, but may not accurately represent the condition of a specific wetland on the ground. Level 2 assessments are rapid, field-based assessments that evaluate the general condition of wetlands using a suite of easily collected and interpreted metrics. The metrics are often qualitative or narrative multiple choice questions that refer to the condition of various attributes (e.g., buffers, hydrology, vegetation, soil surface disruption) based on stressors present on site. Rapid assessments should be conducted within 1–2 hours of field time and are often used to assess a large number of wetlands on the ground to make an overall estimate of condition or evaluate which sites deserve more intensive monitoring. Level 3 assessments involve the most intensive, field-based protocols and are considered the most accurate measure of wetland condition. These assessments are based on quantitative data collection and the establishment of data-driven thresholds. They require skilled practitioners to carry out sampling and can take numerous hours for every site. Level 3 protocols are generally developed separately for different wetland attributes, such as vegetation, macro-invertebrates, water chemistry, hydrology, or wildlife habitat. In some cases, repeat sampling may be necessary to fully capture a wetland’s condition. 2 For more information on EPA’s Level 1-2-3 framework, see http://www.epa.gov/owow/wetlands/pdf/techfram.pdf. http://www.epa.gov/owow/wetlands/pdf/techfram.pdf 6 Within the Level 1-2-3 Framework, data from more detailed levels can be used to calibrate and validate levels above. Level 3 surveys can inform the narrative ratings of Level 2 assessments, and both can help refine Level 1 GIS models. Over time and with sufficient data, coarser level assessments can provide a fairly accurate overview of wetland health across a broad area. However, detailed Level 3 assessments will always provide the most accurate measure of site-specific condition. 1.3.2 NatureServe’s Ecological Integrity Assessment Framework The Ecological Integrity Assessments (EIA) Framework was developed by NatureServe3 and ecologists from several Natural Heritage Programs across the country (Faber-Langendoen et al. 2006; Faber-Langendoen et al. 2008a). The EIA Framework evaluates wetland condition based on a multi-metric index. Biotic and abiotic metrics are selected to measure the integrity of key wetland attributes within four major categories: 1) Landscape context 2) Biotic condition 3) Hydrologic condition 4) Physiochemical condition. Using field and GIS data, each metric is rated according to deviation from its natural range of variability, which is defined based on the current understanding of how wetlands function under reference conditions absent human disturbance. The farther a metric deviates from its natural range of variability, the lower the rating it receives. Numeric and narrative criteria define rating thresholds for each metric. Once metrics are rated, scores are rolled up into the four major categories. Ratings for these four categories are then rolled up into an overall EIA score. For ease of communication, category scores and the overall EIA score are converted to ranks following the ranges shown in Table 1. The scores and ranks can be used to track change and progress toward meeting management goals and objectives. With past funding from EPA Region 8 and CPW, CNHP developed EIA protocols for seven wetland types in the Southern Rocky Mountain Ecoregion (Rocchio 2006a-g), field tested one set of these protocols (Lemly and Rocchio 2009a), and refined the protocols through the Rio Grande Headwater pilot wetland assessment (Lemly et al. 2011). 1.4 Previous Wetland Studies in North Platte River Basin Wetlands in the North Platte River Basin have been the subject of several previous investigations, but none have looked at the entire wetland resource using a random sample survey design that allows for extrapolation. A few studies have discussed the range of wetland types, but most have focused on a particular area of the basin, a particular wetland type, or a particular management question. Selected notable North Platte wetland studies are described here for reference, though this should not be considered an exhaustive list. 3 NatureServe is a non-profit conservation organization whose mission is to provide the scientific basis for effective conservation action. For more information about NatureServe, see their website: www.natureserve.org. http://www.natureserve.org/ 7 Table 1. Definition of Ecological Integrity Assessment ratings. Modified from Faber-Langendoen et al. 2008b. Rank Value Description A Reference Condition (No or Minimal Human Impact): Wetland functions within the bounds of natural disturbance regimes. The surrounding landscape contains natural habitats that are essentially unfragmented with little to no stressors; vegetation structure and composition are within the natural range of variation, nonnative species are essentially absent, and a comprehensive set of key species are present; soil properties and hydrological functions are intact. Management should focus on preservation and protection. B Slight Deviation from Reference: Wetland predominantly functions within the bounds of natural disturbance regimes. The surrounding landscape contains largely natural habitats that are minimally fragmented with few stressors; vegetation structure and composition deviate slightly from the natural range of variation, nonnative species and noxious weeds are present in minor amounts, and most key species are present; soils properties and hydrology are only slightly altered. Management should focus on the prevention of further alteration. C Moderate Deviation from Reference: Wetland has a number of unfavorable characteristics. The surrounding landscape is moderately fragmented with several stressors; the vegetation structure and composition is somewhat outside the natural range of variation, nonnative species and noxious weeds may have a sizeable presence or moderately negative impacts, and many key species are absent; soil properties and hydrology are altered. Management would be needed to maintain or restore certain ecological attributes. D Significant Deviation from Reference: Wetland has severely altered characteristics. The surrounding landscape contains little natural habitat and is very fragmented; the vegetation structure and composition are well beyond their natural range of variation, nonnative species and noxious weeds exert a strong negative impact, and most key species are absent; soil properties and hydrology are severely altered. There may be little long term conservation value without restoration, and such restoration may be difficult or uncertain. The most recent and comprehensive study of wetlands in the North Platte River Basin is the Identification and Assessment of Important Wetlands within the North Platte River Watershed 2009– 2010, conducted by Culver et al. (2010) of CNHP and funded by the Colorado Water Conservation Board. The focus of the 2010 CNHP study was to identify and assess biologically significant wetlands within the basin, with a particular emphasis on rare, uncommon, or significant natural communities and plant and animal populations. The study was designed to assist the North Platte Basin Round Table’s non-consumptives needs assessment sub-committee in identifying important non-consumptive water needs in the basin. The 2010 CNHP study included both public and private lands and resulted in the identification of 68 new occurrences of important wetland resources (plants, animals, or natural communities) and the formation of 32 Potential Conservation Areas across the basin that represent areas of the highest conservation value. Though not a wetland study per se, the North Park Wetlands Focus Area Strategy (North Park Wetlands Focus Area Committee 2002) is also comprehensive and contains a wealth of information about the basin’s wetland resources. Reports or publications that document wetlands within the central North Park valley include three on the Arapaho National Wildlife Refuge (ANWR). The Refuge’s Comprehensive Conservation Plan (USFWS 2004) describes the important role ANWR plays in providing wetland and riparian habitat 8 for many wildlife species in the basin. Lewis’ (2001) floristic survey of ANWR also contains useful information on the Refuge’s wetland plants and plant communities. An earlier report by Knopf and Cannon (1982) documents the effects that past grazing practices continue to exert on willow growth and regeneration on the ANWR. Outside of the Refuge, Johnson and Gerhardt (2004, 2005) conducted ecological investigations of mire and fen wetlands on U.S. Bureau of Land Management (BLM) lands within North Park. Their two reports discuss the location and ecological significance of fen wetlands within the valley, which are relatively rare. A very early article (Davis 1937) provides historical context to the practice of irrigation within North Park. Four publications describe wetlands within the Medicine Bow-Routt National Forest (MBRNF), which includes the basin’s mid and high elevations regions to the west and south. Hay (2010) documents the succession of four beaver pond complexes on the MBRNF over 50 years of observation. Sanders (1997) presents a detailed characterization of montane wetlands and their use by waterfowl. His study includes the physical and chemical composition, aquatic invertebrate community composition, waterfowl numbers and habitat use for 24 wetlands within Big Creeks Lake area of the MBRNF. Kettler and McMullen (1996) surveyed the vegetation of 195 riparian areas across the MBRNF, many of them within the North Platte basin, as part of a statewide classification of riparian plant associations. Johnson (1941) presents an early description of the vegetation surrounding two lakes within the North Platte basin, one within the MBRNF and one, Lake John, within the North Park valley. 9 2.0 STUDY AREA 2.1 Geography The North Platte River Basin is located in north central Colorado (Figure 1) and is the headwaters of the North Platte River. For the purpose of this project, the basin includes only the Colorado portion of HUC6 101800: North Platte River.4 The majority of HUC6 101800 is located in Wyoming and is not included in this Colorado-based study. By only including the Colorado portion, the North Platte is the smallest of ten major river basins in Colorado designated for wetland condition assessment projects under Statewide Strategies for Colorado Wetlands.5 Within the study area there are three HUC8 river subbasins and 68 HUC12 watersheds (Figure 2). Figure 2. HUC8 river subbasins, HUC12 watersheds, and major mountain ranges within the North Platte River Basin. 4 The U.S. Geologic Service (USGS) has divided the Unites States into a hierarchy of hydrologic units, specified by hydrologic unit codes (HUCs). Each level in the hierarchy is noted by the number of digits within the HUC (e.g., HUC6 101800 has 6 digits). The HUC6 level is referred to as the river basin scale. The HUC12 level is referred to as the watershed scale. For more information and to download GIS data, see the website: http://water.usgs.gov/GIS/huc.html. 5 See Lemly et al. (2011) for a map of major river basins designated for wetland condition assessment projects. http://water.usgs.gov/GIS/huc.html 10 The study area encompasses all of Jackson County and the county border follows the study area boundary to the north, west, and south (Figure 1). In the northeast, the river basin includes the Upper Laramie subbasin and the northwest portion of Larimer County. Walden is the largest town in the basin and the center of the basin’s ranching community. Walden supports a population of 608 people and 1,394 people live in all of Jackson County, making it the fourth smallest county in Colorado by population (U.S. Census Bureau 2011). There are no established towns within the Larimer River Valley and few people live there year round. The basin spans ~60 miles (~100 km) from east to west and ~50 miles (~80 km) from north to south, encompassing 1,289,532 acres (2,015 square miles or 521,855 ha). The center of the basin is characterized by a broad high elevation valley known as North Park, the second largest of four intermountain parks in Colorado. The North Park valley is relatively flat, although rolling hills remnant of glacial retreat are present throughout the basin. From the central North Park valley, the basin rises gradually into foothills, then inclines more steeply into the subalpine and alpine zones. Elevations in the basin range from 7,546 ft. (2,300 m) on the valley floor, to a high of 12,951 ft. (3,947 m) at Clark Peak in the Rawah Wilderness. Several other mountain peaks surrounding North Park also surpass 12,000 ft. (3,658 m). The Park Range and Sierra Madre mountains of the Continental Divide delineate the western border of the North Platte River Basin and separate North Platte from the neighboring White- Yampa-Green River Basin to the west. The Rabbit Ears Range, also along the Continental Divide, delineates the southern border of the basin and separates North Platte from the Colorado Headwaters River Basin and Middle Park to the south. To the east, the basin is bounded by Front Range peaks of the Laramie Mountains, which separate north-flowing tributaries of the North Platte River (the Laramie River and Sand Creek) from east-flowing tributaries of the South Platte River. North Park’s central valley and the main North Platte River are separated from the smaller Larimer River Valley by the Medicine Bow Mountains, which slant southeast to northwest. The Laramie River joins the North Platte outside the study area in Wyoming. The Colorado/Wyoming state line delineates the northern edge of the study area, though the North Platte River itself flows on into Wyoming, where it gently arcs east towards Nebraska to join the South Platte. 2.2 Ecoregions and Vegetation Much of the North Platte River Basin falls within the Southern Rocky Mountains Level III Ecoregion (Figure 3: Omernik 19876). The lower portion of the Laramie River Valley, however, is grouped into the Wyoming Basin Level III Ecoregion. Level IV Ecoregions further divide the Southern Rockies landscape into finer units based on geology and dominant vegetation (Table 2; Table 3). In both the Sagebrush Parks and Laramie Basin ecoregions, upland plant communities are mostly dominated by mountain sagebrush (Seriphidium [syn. Artemisia] vaseyanum). Extensive riparian floodplains fill the valleys and predominately contain mixed willow species (Salix monticola and Salix geyeriana). Irrigated hay meadows are also a major land cover, covering approximately 13% of the 6 For more information on Omernik/EPA Ecoregions and to download GIS shapefiles, visit the following website: http://www.epa.gov/wed/pages/ecoregions.htm. http://www.epa.gov/wed/pages/ecoregions.htm 11 basin, and are dominated by meadow foxtail (Alopecurus pratensis)7 or timothy grass (Phleum pratense). In the mountain foothills, vegetation transitions to forests dominated by aspen (Populus tremuloides) and lodgepole pine (Pinus contorta), and many of these forests are affected by mountain pine beetle (Dendroctonus ponderosae) mortality. In the higher subalpine zone, forests are dominated by subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). Above treeline, vegetation consists of mixed graminoids and forbs characteristic of high elevations. Figure 3. Level III and IV Ecoregions within the North Platte River Basin. Level III Ecoregions demarcated by the black like that separates the Wyoming Basin from the rest of the study area. See Table 3 for Level IV Ecoregion descriptions. 7 Some floristic surveys of North Park (Lewis 2001; Culver et al. 2010) include both meadow foxtail (Alopecurus pratensis) and creeping foxtail (Alopecurus arundinaceus). Weber and Wittmann (2001), the primary flora used in this study, does not contain creeping foxtail (A. arundinaceus). For this reason, all observations of non-native foxtails were keyed to meadow foxtail (A. pratensis). 12 Table 2. Level III and IV Ecoregions within the North Platte River Basin. Level III / IV Ecoregion Acres % of Basin 18 Wyoming Basin 72,109 6% 18f Laramie Basin 72,109 6% 21 Southern Rockies 1,217,422 94% 21a Alpine Zone 67,306 5% 21b Crystalline Subalpine Forests 271,907 21% 21c Crystalline Mid-Elevation Forests 125,329 10% 21d Foothill Shrublands 12,483 1% 21e Sedimentary Subalpine Forests 118,343 9% 21f Sedimentary Mid-Elevation Forests 139,341 11% 21g Volcanic Subalpine Forests 10,899 1% 21i Sagebrush Parks 471,815 37% Total 1,289,532 100% Table 3. Descriptions of Level IV Ecoregions within the North Platte River Basin. NAME DESCRIPTION 18f: Laramie Basin The Laramie Basin ecoregion is a wide intermontane valley of Wyoming that extends slightly into northern Colorado. Elevations in the Colorado portion are generally 7800 to 9100 feet, with annual precipitation of 15 to 20 inches. For the region as a whole, natural vegetation is mainly grassland compared to the sagebrush steppe in other regions of Ecoregion 18. Needle-and-thread, western wheatgrass, blue grama, Indian ricegrass and other mixed grass species are typical, along with rabbitbrush, fringed sage and various forb and shrub species. The rolling, high elevation valley of grass and shrubland is used primarily for seasonal livestock grazing. Some hay is produced along the Laramie River. 21a: Alpine Zone The Alpine Zone occurs on mountain tops above treeline, beginning at about 10500 to 11000 feet. It includes alpine meadows as well as steep, exposed rock and glaciated peaks. Annual precipitation ranges from about 35 to greater than 70 inches, falling mostly as snow. Vegetation includes low shrubs, cushion plants and wildflowers and sedges in wet meadows. The forest-tundra interface is sparsely colonized by stunted, deformed Engelmann spruce, subalpine fir and limber pine (krummholz vegetation). Rocky Mountain bristlecone pines, some of the oldest recorded trees in North America, are also found here. Land use, limited by difficult access, is mostly wildlife habitat and recreation. Alpine is snow-free only 8 to 10 weeks annually. Snow cover is a major source of water for lower, more arid ecoregions. 21b: Crystalline Subalpine Forests The Crystalline Subalpine Forests ecoregion occupies a narrow elevational band on the steep, forested slopes of the mountains, becoming more extensive on the north-facing slopes. The elevation range of the region is 8500 to 12000 feet, just below the Alpine Zone. The lower elevation limit is higher in the south, starting at 9000 to 9500 feet. The dense forests are dominated by Engelmann spruce and subalpine fir; aspen and pockets of lodgepole pine locally dominate some areas. Subalpine meadows also occur. Forest blowdown, insect outbreaks, fire and avalanches affect the vegetation mosaic. Soils are weathered from a variety of crystalline and metamorphic materials, such as gneiss, schist and granite, as well as some areas of igneous intrusive rocks. Recreation, logging, mining and wildlife habitat are the major land uses. Grazing is limited by climatic conditions, lack of forage and lingering snowpack. 13 NAME DESCRIPTION 21c: Crystalline Mid-Elevation Forests The Crystalline Mid-Elevation Forests are found mostly in the 7000 to 9000 feet elevation range on crystalline and metamorphic substrates. Most of the region occurs in the eastern half of the Southern Rockies. Natural vegetation includes aspen, ponderosa pine, Douglas- fir and areas of lodgepole pine and limber pine. A diverse understory of shrubs, grasses and wildflowers occurs. The variety of food sources supports a diversity of bird and mammal species. Forest stands have become denser in many areas due to decades of fire suppression. Land use includes wildlife habitat, livestock grazing, logging, mineral extraction and recreation, with increasing residential subdivisions. 21d: Foothill Shrublands The Foothill Shrublands ecoregion is a transition from the higher elevation forests to the drier and lower Great Plains to the east and to the Colorado Plateaus to the west. This semiarid region has rolling to irregular terrain of hills, ridges and foot slopes, with elevations generally 6000 to 8500 feet. Sagebrush and mountain mahogany shrubland, pinyon-juniper woodland and scattered oak shrublands occur. Other common low shrubs include serviceberry and skunkbush sumac. Interspersed are some grasslands of blue grama, june grass and western wheatgrass. Land use is mainly livestock grazing and some irrigated hayland adjacent to streams. 21e: Sedimentary Subalpine Forests The Sedimentary Subalpine Forests ecoregion occupies much of the western half of the Southern Rockies, on sandstone, siltstone, shale and limestone substrates. The elevation limits of this region are similar to the crystalline and volcanic subalpine forests. Stream water quality, water availability and aquatic biota are affected in places by carbonate substrates that are soluble and nutrient rich. Soils are generally finer-textured than those found on crystalline or metamorphic substrates of crystalline subalpine zone and are also more alkaline where derived from carbonate-rich substrates. Subalpine forests dominated by Engelmann spruce and subalpine fir are typical, often interspersed with aspen groves or mountain meadows. Some Douglas-fir forests are at lower elevations. 21f: Sedimentary Mid-Elevation Forests The Sedimentary Mid-Elevation Forests ecoregion occurs in the western and southern portions of the Southern Rockies, at elevations generally below sedimentary subalpine forest. The elevation limits and vegetation of this region are similar to the crystalline and volcanic mid-elevation forests; however, a larger area of Gambel oak woodlands and forest is found in this region. Carbonate substrates in some areas affect water quality, hydrology and biota. Soils are generally finer-textured than those found on crystalline and metamorphic substrates such as those in the crystalline mid-elevation forest. 21g: Volcanic Subalpine Forests The steep, mountainous Volcanic Subalpine Forests ecoregion is composed of volcanic and igneous rocks, predominately andesitic with areas of basalt. The region is found mainly in the San Juan Mountains, which have the most rugged terrain and the harshest winters in the Southern Rockies of Colorado. Smaller areas are found in the West Elk Mountains, Grand Mesa, Flat Tops and in the Front Range. The area is highly mineralized and gold, silver, lead and copper have been mined. Relatively young geologically, the mountains are among the highest and most rugged of North America and still contain some large areas of intact habitat. Engelmann spruce, subalpine fir and aspen forests support a variety of wildlife. 21i: Sagebrush Parks The Sagebrush Parks ecoregion contains the large, semiarid, high intermontane valleys that support sagebrush shrubland and steppe vegetation. The ecoregion includes North Park, Middle Park and the Gunnison Basin and is slightly drier than the Grassland Parks. Summers tend to be hot and winters very cold, with annual precipitation of 10-16 inches. Land use is mostly rangeland and wildlife habitat, with some hay production near streams. The sagebrush provides forage and habitat to many animals and birds. Sandy loam soils are typical, formed in residuum from crystalline and sedimentary rocks, glacial outwash and colluvial or alluvial materials. 14 2.3 Geology The central North Park valley is a synclinal basin. The syncline is a structural fold where the underlying strata dip toward the center of the structure, resulting in older strata being exposed at the margins of the basin and younger strata toward the center (Figure 4). In the central portion of the basin, North Park’s geology is comprised of sedimentary formations with alluvial soil depositions along the riparian floodplains and foothills of the Park Range (Tweto 1979). The basin’s foothills and the Larimer Valley are comprised of a mix of sedimentary shale, sandstone, siltstone, and mudstone depositions. Patches of unconsolidated sand form dunes in the western foothills of the Medicine Bow Mountains. Sedimentary formations in North Park began layering as long ago as the Permian age and are as deep as 19,000 ft. (5800 m; Voegeli 1965). The Coalmont formation that spans ~75% of the North Park valley is rich in soft coal, and the deep sedimentary layers also contain petroleum resources. In contrast, parent geology of the basin’s mountains consists of older Precambrian metamorphic or igneous rock formed in the Laramide Orogeny (Dickenson 1988). Figure 4. Dominant geology of the North Platte River Basin. 15 2.4 Climate and Hydrology The semi-arid climate of the North Platte River Basin is characterized by long cold winters and short summers, and the harsh conditions limit year-round human populations. Mean annual temperatures average 37°F in Walden, and average maximum temperatures are 78° and 76°F in the warmest months of July and August (WRCC 2011). At the weather station in Walden, precipitation averages 11 in (27 cm)/year and snowfall averages 58 in (146 cm)/year. Precipitation increases to 14 in and snowfall increases to 98 in snowfall at the weather station in Rand in the mountain foothills. Temperature and precipitation peak in the summer, but on average, only the months of July and August receive no snowfall in the valleys and the mountains peaks hold snow-pack year round. Climatic conditions in the surrounding mountains (at higher elevations than the WRCC weather stations) have more extreme lows, more snowfall and more precipitation. The long winters, short growing season, and lack of developed winter resorts lend to the basin’s character and have strongly affected current and historical human land use and settlement patterns. The North Platte River and its tributaries collect all major runoff in the basin, directing the flow north past the Colorado/Wyoming state line through Northgate Canyon. The North Platte itself is a significant tributary of the Platte River, which is formed at the confluence of the North and South Platte Rivers in western Nebraska and flows east to the Mississippi River before emptying into the Gulf of Mexico. The collective length of the North Platte and Platte Rivers is 716 miles (1,152 km) long (USGS 2011). Within Colorado, major tributaries of the North Platte River include Arapaho Creek, Canadian River, Colorado Creek, Grizzly Creek, Illinois River, Laramie River, Michigan River, North Fork of the North Platte River, Sand Creek, and Willow Creek (Figure 2). At the Northgate stream flow gaging station, mean annual flow of the North Platte River is ~312,000 acre-feet (USGS 2012). Mean annual flow of the Laramie River at Glendevey is ~52,000 acre-feet. There are twelve major reservoirs in the basin that store ~34,000 acre-feet (not including Chambers Lake at the headwaters of the Laramie River). Three major trans-basin diversions export water from the North Platte for use in the South Platte River Basin. In total ~23,000 acre-feet are diverted from the basin (CWCB 2012). Possibly as much as 78% of the precipitation that falls in the basin is lost to evaporation from open water, snow, and ice and by transpiration from vegetation (Robson and Graham 1996). 2.5 Land Ownership and Land Use The first people documented to use the North Platte basin entered from Wyoming along the North Platte River to hunt large mammals during warm seasons. Ancient spear points indicate the mammoth hunting Clovis people entered the valley perhaps 11,000 years ago, during a time when intermountain canyons in the west portion of the basin were laden with glaciers (Richard 2009). Over thousands of years, various Native American tribes continued to seasonally hunt in the basin known for its abundant game, particularly bison, antelope, elk, deer, and bighorn sheep. As Euro- Americans explorers and trappers arrived in the basin in the 1830s, they used hunting methods learned from the Ute tribes and bison populations were severely reduced. Trapping for fur also decimated beaver and other wildlife populations. Over the next 100 years, increasing human presence and ranching settlements decreased ungulate, wolf, bear, and sage grouse populations. 16 Many populations were either significantly reduced or eradicated (Richard 2009). Major predators and bison have not returned to North Park, however, USFWS and CPW now intensively manage ungulate herds and nesting bird populations and reservoirs are stocked with trout. Once again, the basin is known for its wildlife resources and sportsmen and wildlife viewers travel to North Park for fish, elk, antelope, deer, moose, and birds. Knowledge of wetland location, type, and condition is particularly pertinent to the management of wildlife species that depend on wetlands for their habitat. Today, the majority of land throughout the basin is owned by public entities (Figure 5). Only 33% of the basin is in private hands and these lands are concentrated in the central North Park valley. Along with private lands, North Park also contains lands managed for grazing by the Colorado State Land Board (SLB) and Bureau of Land Management (BLM) and lands managed for wildlife, including USFWS’s Arapaho National Wildlife Refuge and several CPW State Wildlife Areas. The basin’s mountains are mostly managed by the U.S. Forest Service (USFS). Western and southern mountains are within the Medicine Bow-Routt National Forest while eastern mountains are within the Arapaho-Roosevelt National Forest. USFS lands also contain the Mount Zirkel, Rawah, and Never Summer Wilderness Areas. A very small portion of Rocky Mountain National Park extends into the southeast corner and State Forest State Park spans the western foothills of the Laramie Mountains. Figure 5. Land ownership within the North Platte River Basin. 17 Since the time of early settlement in the 1870s, the dominant land use in the basin has been cattle ranching. Hay production is a major supplement to the ranching income and provides livestock feed, however, climatic conditions only allow one hay cutting per year, unlike many other areas in Colorado that can sustain two yearly harvests. Seasonal wildlife tourism is also important, including game-viewing, hunting, and fishing in basin’s lakes and streams. Dude ranches and summer vacation homes located in the North Park and Laramie River valleys add to the tourism economy based on the ranching lifestyle. The basin is relatively remote when compared with much of Colorado. Less than 0.03% of the basin is classified as low, medium, or high intensity developed land, and high intensity development makes up < 2 acres total (Landfire 2008). Water movement and irrigation is integral to ranching in intermountain valleys. Anthropogenic hydrologic alterations in the basin began in the 1880s, shortly after settlers first overwintered. Concentrating near streams in the otherwise dry environment, they dug shallow ditches throughout much of North Park to expand the floodplain resources for their cattle, and many of these small, unlined ditches remain today. Irrigation reached its peak in North Park in 1939 with 131,810 acres (North Park Wetlands Focus Area Committee 2002). The current extent of irrigated lands is closer to 110,000 acres (CDDS 2009) and the legal limit based on inter-state water law is 145,000 acres (CWCB 2012). Existing irrigated land is still concentrated near the rivers and their broad, meandering, floodplains. Every spring, landowners flood irrigate their lands for hay and cattle, which has created additional wetland acres over many years (Peck and Lovvorn 2001). As a result, teasing out natural from created wetlands in areas where flood irrigation occurs is nearly impossible. Fed by spring snowmelt, surface water is generally abundant and diverted in shallow ditches from streams for localized flood irrigation. Groundwater pumping is much lower than in other more intensively managed agricultural regions of Colorado, such as the Rio Grande Headwaters or the eastern plains. Only 130 active water wells are reported in North Park and many of these are under 120 feet deep (CDWR 2011). Resource extraction has been a continuous but small share of the economy since Euro-American settlement. It began with soft coal extraction from the Coalmont Formation, was followed by gold and other metal extraction from placer mines from 1874 to the early 1900s (Athearn 1977), and later expanded to drilling the thick sedimentary layers for petroleum beginning in the 1920s. Between the 1930s–1980s, commercial logging took place in the forested mountains and foothills. In recent years, hydraulic fracturing has been used to extract natural gas from deep within the sedimentary formations throughout North Park. Oil and gas well density (COGCC 2011) is currently lower in this region than some other areas in Colorado, such as Weld County, but development of wells that use hydraulic fracturing substantially increased from 2007 to 2011, with more leases pending. Drilling for oil and gas is often contentious in pristine places popular with sportsmen, and there is concern that increasing oil and gas development in North Park may degrade important wildlife habitat (Ellenberger and Byrne 2011). 18 3.0 METHODS 3.1 Wetland Profile and Landscape Integrity Model At the outset of this project, digital wetland mapping from U.S. Fish and Wildlife Service (USFWS)’s National Wetland Inventory (NWI) program was available for less than 10% of the basin, though paper maps drawn between the late 1970s and early 1980s existed for the entire area. To create the wetland profile, original paper maps for all topographic quads lacking digital spatial data were scanned and converted to geo-rectified digital polygons, producing a wall-to-wall map of wetlands in the basin. The maps were not updated in the digital conversion, but land use change in the basin has been minimal in the 30 years since the maps were drawn. The digitization process was completed concurrently with this project, but was funded through the original Statewide Strategies for Colorado Wetlands grant (EPA Assistance ID# CD-97874301-0; Lemly et al. 2011). Based on completed digital NWI mapping and ancillary data sources, a detailed wetland profile for the North Platte River Basin was prepared. The profile summarizes the extent of wetland acreage throughout the basin by NWI system/class, hydrologic regime, extent modified, extent irrigated, land ownership, and Level IV Ecoregions. Along with the wetland profile, a Level 1 assessment of wetland condition within the entire river basin and each ecoregion was conducted based on a statewide Wetland Landscape Integrity Model (LIM) developed previously (Lemly et al. 2011). The model is a weighted algorithm combining several landscape level stressors derived from GIS into an overall landscape integrity score. The weighting was based on best professional judgment of each stressor’s relative impact. For most stressors, a distance decay function was used to account for the fact that impacts fade with distance in a non-linear fashion. 3.2 Survey Design and Site Selection The following paragraphs detail the survey design for the field-based component of the North Platte River Basin wetland condition assessment, including the target population, classification, sample size, sample frame, and selection criteria. The survey design follows principles outlined by the EPA’s EMAP program (Stevens & Olsen 2004; Detenbeck et al. 2005). 3.2.1 Target Population The target population for this study was all naturally occurring and naturalized vegetated wetlands within the North Platte River Basin. The target population did not include deep water lakes or stream channels, though we report out the acreage of these features in the wetland profile. During the study, the target population was modified to exclude actively managed hay pastures (see Section 3.2.5 for explanation). Minimum size criteria of 0.1 hectares in area and 10 m in width were also implemented. For safety reasons, we excluded wetland area with water > 1 m deep from field sampling. The operational definition used in this project is the USFWS definition used for NWI mapping (Cowardin et al. 1979): 19 “Wetlands are lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. For purposes of this classification wetlands must have one or more of the following attributes: (1) at least periodically, the land supports predominantly hydrophytes; (2) the substrate is predominantly undrained hydric soil; and (3) the substrate is nonsoil and is saturated with water or covered by shallow water at some time during the growing season of each year.” The USFWS definition is different than the definition of wetland used by the ACOE and the EPA for regulatory purposes under Section 404 of the Federal Clean Water Act (ACOE 1987): “[Wetlands are] those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.” The primary difference between the two definitions is that the Clean Water Act definition requires positive identification of all three wetland parameters (hydrology, vegetation, and soils) while the USFWS definition requires only one to be present. It is important to note that wetlands surveyed through this study may or may not be classified as jurisdictional wetlands under the Clean Water Act and that NWI mapped boundaries should not be interpreted as wetland delineations. We used standard wetland identification and delineation techniques to determine inclusion in the sample population. We relied heavily on materials produced by the U.S. Army Corps of Engineers (ACOE) and the Natural Resources Conservation Service (NRCS), such as the Interim Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Western Mountains, Valleys, and Coast Region (ACOE 2008) and the Indicators of Hydric Soils in the United States (NRCS 2010). However, we only needed positive identification of one or two parameters, not all three. NWI mapping also includes non-vegetated areas and deep water habitats, which were excluded from this study. Though the original sample frame (NWI mapping) was refined by excluding non- target attribute classes (see Section 3.2.4), the remaining sample frame still included non-target areas that were rejected through desktop review or on-site evaluation. 3.2.2 Subpopulations/Classification The target population was classified into subpopulations based Ecological Systems (Table 4; Comer et al. 2003). Because elements within the sample frame (NWI polygons) were not attributed according to the Ecological System classification, these subpopulations were not part of the survey design a priori. Individual estimates of condition were calculated post hoc for subpopulations where sufficient data were collected. The Ecological System classification is a component of the International Vegetation Classification System (Grossman et al. 1998; NatureServe 2004; Faber-Langendoen et al. 2009), developed by NatureServe and the Natural Heritage Network. It provides a finer scale of resolution than traditional wetland classification systems such as the USFWS’s Cowardin classification (Cowardin et al. 1979) and the hydrogeomorphic (HGM) classification system (Brinson 1993). The Ecological System approach uses both biotic (structure and floristics) and abiotic (hydrogeomorphic template, 20 elevation, soil chemistry, etc.) criteria to define units. These finer classes allow for greater specificity in developing conceptual models of the natural range of variation and in setting thresholds that relate to stressors. Sites were classified by Ecological Systems following the key in Appendix A. While Ecological Systems was the primary classification system used, each sampled wetland was also classified onsite by the HGM (Appendix B) and Cowardin systems in order to report on numbers of sites and scores by those systems as well. Table 4. Wetland Ecological Systems found in the North Platte River Basin. Ecological System Inter-Mountain Basins Alkaline Closed Depression Rocky Mountain Alpine-Montane Wet Meadow Rocky Mountain Subalpine-Montane Fen Rocky Mountain Subalpine-Montane Riparian Shrubland Rocky Mountain Subalpine-Montane Riparian Woodland Western North American Emergent Freshwater Marsh 3.2.3 Sample Size The target number of sample sites was 100, stratified by Level IV Ecoregion. However, not all sites were able to be sampled given access issues and time constraints. Over the 2010 field season, 95 wetland sites were sampled. 3.2.4 Sample Frame The sample frame was based on digital polygons converted from original NWI paper maps. From the NWI dataset, we eliminated all polygons that represented unvegetated surfaces, deep water lakes, river and stream channels, and unvegetated irrigation ditches. A list of NWI codes included in and excluded from the sample frame can be found in Appendix C. To build the final sample frame, all area within the included NWI polygons was converted into a 10-meter grid of potential sample points. A 10-meter grid was chosen as the smallest sample unit possible under the constraints of computer processing time and file size, but ensured that even small polygons would include points. Target sample points were selected from within this grid of points and not from polygon centroids because of extreme variation in the size of individual polygons. All estimates made during analysis are for wetland area, not percent or number of individual wetlands. 3.2.5 Selection Criteria The study employed a one-stage survey design stratified by Level IV Ecoregions (see Section 2.2). The study area contains nine Level IV Ecoregions. However, to reduce the number of strata, Level IV Ecoregions that occupied < 5% of the study area were combined with similar ecoregions. Ecoregion 21g: Volcanic Subalpine Forests was combined with 21b: Crystalline Subalpine Forests and ecoregion 21d: Foothill Shrublands was combined with 21f: Sedimentary Mid-Elevation Forests and Shrublands. Target sample points were selected from each of the resulting seven ecoregional strata using the Reversed Randomized Quadrant-Recursive Raster (RRQRR) approach in ArcGIS 9.3 (Theobald