Methods for Converting Continuous Shrubland Ecosystem Component Values to Thematic National Land Cover Database Classes Open-File Report 2017–1119 U.S. Department of the Interior U.S. Geological Survey Cover. Sagebrush steppe, Boars Tusk, southwest Wyoming. Photograph by Collin G. Homer, U.S. Geological Survey. Methods for Converting Continuous Shrubland Ecosystem Component Values to Thematic National Land Cover Database Classes By Matthew B. Rigge, Leila Gass, Collin G. Homer, and George Z. Xian Open-File Report 2017–1119 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S. Geological Survey William H. Werkheiser, Acting Director U.S. Geological Survey, Reston, Virginia: 2017 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. 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ISSN 2331-1258 (online) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Section I—Modelling Thematic Land Cover from Continuous Cover Classes ....................................2 Model Input Data ..................................................................................................................................2 Component Indicators ..........................................................................................................................2 Main Model ............................................................................................................................................6 Final Thematic Classification ..............................................................................................................6 Other Considerations............................................................................................................................6 Section II—Preparation of Validation Data ...............................................................................................6 Section III—Accuracy Assessment ...........................................................................................................8 Conclusion.....................................................................................................................................................10 Summary........................................................................................................................................................10 Acknowledgments .......................................................................................................................................10 References Cited..........................................................................................................................................10 Figures 1. Map showing continuous cover shrubland mapping products “cross-walked” to barren, shrubland, and grassland thematic classes superimposed on National Land Cover Database (NLCD) 2011 thematic map and original NLCD 2011 ..................................3 2. Diagram showing selected inputs into the National Land Cover Database cross-walk model and continuous cover predictions of shrub cover, herbaceous cover, and bare ground cover, near the Black Rock Desert, Nevada .................................5 3. Data processing flow chart for “cross-walking” continuous cover shrubland layers into National Land Cover Database thematic classes ...........................................................7 4. Graphs showing percentage of area in cross-walk classes within National Land Cover Database 2011 classes by region ...................................................................................9 Tables 1. Thematic accuracy assessment results of the National Land Cover Database 2011 and continuous cover mapping crosswalk in all areas; Wyoming, Montana, and Black Hills; and Great Basin as compared to independent validation data developed for the continuous cover mapping .............................................................................................8 2. Thematic accuracy assessment results of the National Land Cover Database 2011 and continuous cover crosswalk as compared to training data sites used in the development of continuous cover components ......................................................................9 3. Frequency of thematic classes within the crosswalk product and National Land Cover Database 2011, based on a sample of 10,000 random points across each region ..............................................................................................................................................9 iv Conversion Factors International System of Units to U.S. customary units Multiply By To obtain Length meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) kilometer (km) 0.5400 mile, nautical (nmi) meter (m) 1.094 yard (yd) Area square meter (m2) 0.0002471 acre square meter (m2) 10.76 square foot (ft2) Abbreviations LI life indicator NLCD National Land Cover Database SC shrub code SV shrub volume USGS U.S. Geological Survey WV–2 WorldView 2 Methods for Converting Continuous Shrubland Ecosystem Component Values to Thematic National Land Cover Database Classes By Matthew B. Rigge, Leila Gass, Collin G. Homer, and George Z. Xian Abstract “cross-walked” product, where available, in the NLCD 2016 product. The National Land Cover Database (NLCD) provides thematic land cover and land cover change data at 30-meter spatial resolution for the United States. Although the NLCD Introduction is considered to be the leading thematic land cover/land use product and overall classification accuracy across the NLCD The National Land Cover Database (NLCD) consists of is high, performance and consistency in the vast shrub and land cover and land cover change data for the United States at grasslands of the Western United States is lower than desired. the native 30-meter (m) spatial resolution of the Landsat The- To address these issues and fulfill the needs of stakehold- matic Mapper (Homer and others, 2015). The NLCD currently ers requiring more accurate rangeland data, the USGS has includes data for 2001, 2006, and 2011, and the 2016 edition developed a method to quantify these areas in terms of the is in production. NLCD products are used in many applica- continuous cover of several cover components. These compo- tions, including biology, climate, planning, land manage- nents include the cover of shrub, sagebrush (Artemisia spp), ment, hydrology, and education. Although the overall user’s big sagebrush (Artemisia tridentata spp.), herbaceous, annual accuracy for the 2001, 2006, and 2011 NLCD products has herbaceous, litter, and bare ground, and shrub and sagebrush been about 83 percent (Wickham and others, 2017), correctly height. To produce maps of component cover, we collected distinguishing among the rangeland/shrubland classes of bar- field data that were then associated with spectral values in ren, grassland, and shrubland is difficult, with user’s accuracy WorldView-2 and Landsat imagery using regression tree for these classes in the Western United States reported at 46, models. The current report outlines the procedures and results 56, and 73 percent, respectively. of converting these continuous cover components to three Because characterizing and quantifying distributions of thematic NLCD classes: barren, shrubland, and grassland. To shrubland ecosystem components is one of the major chal- accomplish this, we developed a series of indices and condi- lenges for monitoring vegetation cover change in the Western tional models using continuous cover of shrub, bare ground, United States, U.S. Geological Survey (USGS) scientists herbaceous, and litter as inputs. The continuous cover data are developed a method to quantify continuous cover of shru- currently available for two large regions in the Western United bland components (Xian and others, 2013). This method has States. Accuracy of the “cross-walked” product was assessed undergone several rounds of methodological improvements. In relative to that of NLCD 2011 at independent validation points the latest effort of Xian and others (2015), researchers (1) col- (n=787) across these two regions. Overall thematic accuracy lected field ocular estimates of component cover correspond- of the “cross-walked” product was 0.70, compared to 0.63 for ing with vegetation patches visible on WorldView 2 (WV–2) NLCD 2011. The kappa value was considerably higher for the (2-m resolution)