Wet meadow and fen mapping of Yosemite National Park: A photo interpretation mapping project of wetland resources

Pyrooz, Natalie; Dickenson, Adam; Nesmith, Jonathan; Cann, Corie; Frenzel, Erik; Haultain, Sylvia; Hardwick, Paul

Wetlands are some of the most diverse and ecologically important ecosystems on earth, yet they are also some of the most threatened. In the Sierra Nevada, meadows (both wet and dry) are estimated to occupy roughly 2% of the land area and 40–60% of these systems are in a degraded condition due to historic or current land use. Wet meadows and fens are a subset of wetlands that are largely groundwater dependent and are characterized by high water tables, organic soils, and herbaceous plant communities. The Yosemite Wetland Mapping Project was an effort conducted by the National Park Service Inventory & Monitoring Program, Sierra Nevada Network (SIEN) to identify and map all fens and wet meadows >0.5 ha within Yosemite National Park (YOSE). The aim of this mapping project was to create a feature class that shows all wet meadows and fens greater than 0.5 ha within Yosemite National Park, and classifies them as wet meadow, fen-meadow complex, and fen. This work complemented a previous effort to characterize similar habitat using the same procedures in Sequoia and Kings Canyon National Parks. Wetland mapping was conducted by two technicians based on aerial imagery photo interpretation during the winter of 2014. Multiple years of true color and color infrared National Agriculture Imagery Program imagery were used to map and classify target wetlands based on color signature, texture, vegetation density, slope, and expert knowledge of park wetlands. Other key data that were used to inform mapping decisions included meadow field survey data, the YOSE vegetation map, wetland mapping data from the SIEN Wetland Ecological Integrity pilot study, and the National Wetlands Inventory data. All mapping was done using Environmental Systems Research Institute ArcGIS 10.1 software with versioning that allowed the two technicians to work simultaneously on the same feature class. A total of 1,605 wetland polygons and 557 points of peat-accumulating areas were created. Seventeen polygons represent fens, 297 represent fen-meadow complexes, and the remaining 1,291 represent wet meadows within YOSE. The total area of wet meadows, fen-meadow complexes, and fens mapped was 4,307 ha, which is 1.4% of the total acreage of the park. Overall classification accuracy was estimated to be 63% (90% CI = 56–70%) based on field assessments of 139 polygons that included both target wetlands mapped by this project, as well as areas that were mapped as seasonal or perennial wetlands on the YOSE vegetation map, but were deemed to not meet the definition of a target wetland for this project. When only target vs. non-target status was considered, mapping accuracy improved to 84%, indicating that most of the mapping errors occurred when trying to distinguish among target wetland types (fen, wet meadow, or fen-meadow complex). When these error rates are taken into account, the estimated area of fen and wet meadow habitat in YOSE is 3,730 ha (1.2% of the total area of the park). The products from this project will allow managers to better understand the distribution and current status of fens and wet meadows within YOSE. This information is already being used to aid several NPS planning and monitoring efforts including the SIEN Wetland Ecological Monitoring Protocol.

Wet meadow and fen mapping of Yosemite National Park: A photo interpretation mapping project of wetland resources

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