Vegetation Classification and Mapping Project Report, Natural Bridges National Monument

Coles, Janet; Von Loh, Jim; Evenden, Angela; Manis, Gerald; Wakefield, Gery; Wight, Aneth

The Northern Colorado Plateau Inventory and Monitoring Network (NCPN) worked with the U.S. Geological Survey (USGS) and National Park Service (NPS) Vegetation Characterization Program to describe and map vegetation at Natural Bridges National Monument. This collaborative effort involved many project partners, particularly engineering-environmental Management (e2M), the Western Region office of NatureServe, and their cooperators.The total project mapping area is 5,378 hectares (13,290 acres), encompassing the Monument and environs. Ecologists, botanists, and photo interpreters worked together to identify plant associations for NABR and determine how best to map them using 1:12,000-scale, true color aerial photography. The team collected vegetation and environmental data from 80 vegetation classification plots and 17 observation points. No supplemental fuels data were collected during the project. Fieldwork and mapping were completed between 2003 and 2005.Analysis of the plot data revealed 35 National Vegetation Classification plant associations or park special vegetation types within the Monument and environs. Four of these associations were added to the classification following an analysis of the accuracy assessment data in the latter stages of the project. Three unvegetated land use/land cover types were delineated, including roads and Monument facilities.Vegetation and land use were interpreted to as detailed a level as possible from high resolution, true color digital orthophotographs and 9” x 9” stereo pairs of 1:12,000-scale true color aerial photography flown specifically for this project. Polygons representing vegetation or land use map classes were delineated on orthophotographs and later transferred to a spatial database.A total of 1232 map polygons representing 16 natural and semi-natural vegetation map classes were developed within the NABR mapping project area. Three land use map classes described 18 polygons within the mapping area. Average polygon size across all map classes is 4.3 ha (10.6 acres). One map class (Hanging Gardens) occurs consistently in patches smaller than the minimum mapping unit of 0.5 ha and is represented by point data.Map accuracy was assessed within the NABR boundary only. Results from a thematic accuracy assessment of 14 vegetation map classes indicated an overall map accuracy of 86.8% (Kappa index = 85.0%). Five map classes did not meet the 80% accuracy standard, but were retained because of their relative rarity and value to Monument managers. These are described in detail in the Accuracy Assessment section of this report, along with the justification for retaining them.

Vegetation Classification and Mapping Project Report, Natural Bridges National Monument

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