San Juan Island National Historical Park vegetation classification and mapping project report

Rocchio, F.; Crawford, Rex; Copass, Catharine

The National Park Service (NPS) Vegetation Inventory Program (VIP) is an effort to classify, describe and map existing vegetation of national park units for the NPS Natural Resources Inventory and Monitoring Program. The Washington Natural Heritage Program (WNHP), working in cooperation with the North Coast and Cascades Network (NCCN), has completed a vegetation classification and map of San Juan Island National Historical Park (SAJH). Every vegetation type within the park was classified and mapped to at least the NVC Alliance level, and many were classified and mapped to the Association level. Classification data collection occurred simultaneously with field-based mapping. Collection of new data occurred in 171 plots and was designed to fill known gaps in the existing classification, to document the occurrence of known associations, and to identify previously unrecognized associations. A vegetation key was developed to enable future users to identify plant associations or alliance types in the field. New or edited summary descriptions were written for all plant association or alliance types. There were 49 alliances classified as occurring within SAJH. Forested alliances accounted for 31%, shrubland/herbaceous alliances totaled 67%, and the single sparse alliance accounted for 2% of the total number of alliances. An additional nine map units were used for Cultural and Non-vegetated cover types. Three “Alliance” level units were documented for cultural vegetation including one unit for Agromorphic and two units for Developed vegetation classes. There were also an additional six map units identified for non-vegetated cover types.Nearly 43% of the vegetation alliances were classified as ruderal types, indicating that past land use has resulted in numerous novel vegetation types dominated by non-native vegetation or combinations of native species with no similar type existing in ‘natural’ landscapes. The most frequent alliance and the alliance covering the greatest area (317.3 ha or 784.2 acres) is the Pseudotsuga menziesii - (Arbutus menziesii) Forest and Woodland Alliance. The Symphoricarpos albus Pacific Coast Shrubland Alliance was the most frequent and most abundant shrub alliance. The Holcus lanatus - Poa pratensis - Elymus repens Provisional Ruderal Alliance dominated the herbaceous areas (104.8 ha or 259.1 acres). The validation and accuracy assessment process are external to development of the map and provides a neutral evaluation of the map and were accomplished by Rex Crawford, WNHP ecologist who played no role in the mapping project prior to these tasks. Validation and accuracy assessment took place at 354 sample points. The accuracy assessment at the alliance-level has an overall accuracy of 82.0 ± 5.2% (90% confidence intervals). The Kappa index was 82.1% ± 3.5% (90% C.I.). This meets the accuracy requirement of 80% established by the National Park Service Vegetation Inventory Program.

San Juan Island National Historical Park vegetation classification and mapping project report

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