Vegetation map of Virgin Islands National Park, St. John, United States Virgin Islands

Thanawastien, Tiara; Whelan, Kevin; Shamblin, Robert; Giannini, Helena; Patterson, Judd; Ruiz, Pablo

doi:10.36967/nrr-2293266

In 2009, the National Park Service (NPS) Vegetation Mapping Inventory funded the NPS South Florida Caribbean Network (SFCN) to evaluate the accuracy of a vegetation map produced by the University of the Virgin Islands (UVI) Eastern Caribbean Center, Conservation Data Center for Virgin Island National Park (VIIS). The UVI vegetation map of VIIS was completed in 2001 and was based on aerial imagery from 1994. VIIS park staff felt that the UVI vegetation map was relatively accurate, but recognized that no formal accuracy assessment of the product had occurred at the time of its creation. The report that follows details the methods used by SFCN to 1) assess the accuracy of the 1994 UVI vegetation map of VIIS, and 2) create a new vegetation map for VIIS using aerial imagery from 2006-07 and Light Detection and Ranging (LiDAR) data. In addition, it contains an analysis of the UVI and SFCN vegetation maps, the accuracy assessment results for both vegetation maps, the vegetation classification key used, and the photo-interpreter key used on the SFCN vegetation map. Both the UVI and SFCN vegetation maps of VIIS relied on aerial imagery and photo-interpreters to delineate vegetation communities. However, the SFCN vegetation map had the benefit of having LiDAR data available; a technology and data source not readily available when the UVI vegetation map was produced. In addition, the SFCN vegetation map benefited from technological advances in aerial image acquisition that significantly improved the quality and resolution of imagery used; GPS that allowed precise spatial location determination; and GIS science that permitted the viewing, layering, and manipulation of multiple data sources simultaneously. The SFCN vegetation map also benefitted from the use of digital orthophotographs that take into account the surface elevation, topography, of the earth and camera tilt. The UVI vegetation map has an estimated map accuracy of 45.9% with a lower 90th Percentile Confidence Interval of 38.5% while the SFCN vegetation map accuracy is estimated at 87.9% with a lower 90th Percentile Confidence Interval of 82.0%. The SFCN vegetation map has approximately 2.1 times more detail, in the form of individual patches, than the UVI vegetation map does, 1,430 vs 686 patches, respectively. Mean patch size and maximum patch size are smaller in the SFCN vegetation map than in the UVI vegetation map. This results in the SFCN vegetation map being less homogeneous than the UVI map even though the total number of community types mapped are nearly identical, 27 vs 29.

Vegetation map of Virgin Islands National Park, St. John, United States Virgin Islands

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