Vegetation Classification and Mapping Project Report [and associated files], Arches National Park

Coles, Janet; Tendick, Amy; Manis, Gerald; Wight, Aneth; Wakefield, Gery; Von Loh, Jim; Evenden, Angie

The Northern Colorado Plateau Inventory and Monitoring Network, with the support of the U.S. Geological Survey - National Park Service Vegetation Mapping Program, undertook this project to describe and map existing vegetation at Arches National Park (ARCH). This collaborative effort involved many project partners, particularly the Natural Resources staff of the Southeast Utah Group of National Parks, the Western Region office of NatureServe, engineering-environmental Management, Inc., and their cooperators. The mapping area is 52,556 hectares (129,868 acres), encompassing the entire park as well as an environs of adjacent public and private lands. Ecologists and photointerpreters identified plant associations for ARCH and determine how best to map them using 1:12,000-scale, true color aerial photography and digital orthophotography. The team collected vegetation and environmental data from 333 vegetation classification plots and 256 observation points. Map accuracy assessment entailed sampling another 792 plots. No supplemental fuels data were collected during the project. Fieldwork and mapping were completed between 2003 and 2005. Analysis of the plot data revealed 75 National Vegetation Classification plant associations, alliances or park special vegetation types within the Park and environs. Five associations were documented from accuracy assessment data, the remainder from vegetation classification plots and observation points. Vegetation and land use were interpreted to as detailed a level as possible from high-resolution, 9” x 9” stereo pairs of 1:12,000-scale true color aerial photography. Polygons representing vegetation or land use map classes were delineated on-screen in an ArcGIS environment. The project used the program standard minimum mapping unit of 0.5 ha with few exceptions. Thirty-one (30 polygon and 1 point) natural and semi-natural vegetation map classes were developed for the ARCH mapping project, represented by 6,709 map polygons. Twelve land use map classes describe 193 other polygons within the mapping area. An additional 222 polygons represent exposures of two unvegetated geologic formations. Average polygon size across all map classes is 7.3 ha (18.0 acres). Natural and semi-natural vegetation classes cover 52,521 ha (124,171 acres / 95.6% of the project area). Map classes representing unvegetated bedrock total 1,295 ha (3,200 acres / 2.5% of the project area). Land use/land cover polygons, including roads, commercial developments, mining facilities and NPS facilities total 1,010 ha (2,497 acres / 1.9% of the project area). The most frequent vegetation mapping unit is Blackbrush Shrublands (Map Class 10 / S-BLAC) with 1,457 polygons covering 9,073 ha (22,407 acres) or 17% of the project area. Map accuracy was assessed within the ARCH boundary only. Analysis of a thematic accuracy assessment of 30 polygon-based vegetation map classes indicated an estimate of 90.1% overall map accuracy (Kappa statistic = 89.9%). One map class did not meet the 80% standard for either producer’s or user’s accuracy, but was retained because of its uniqueness and value to park managers. The patterns of error are described in detail in the Accuracy Assessment section of this report, along with the justification for retaining the map class with relatively low accuracy.

Vegetation Classification and Mapping Project Report [and associated files], Arches National Park

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