Historical Surface Cover Analysis of the Point Conception Headland Bypass Dune System at the Jack and Laura Dangermond Preserve, CA

Abstract:
<p>Aerial imagery from 1929-2023 shows increasing vegetation cover across the surface of the Point Conception headland bypass dune system (HBDS) at the Jack and Laura Dangermond Preserve (JLDP). Ice plant (<i>Carpobrotus edulis</i>), an invasive succulent, currently has widespread surface cover and likely has expanded since 1929. The rate of vegetation expansion and amount of surface cover change across the HBDS had yet to be quantified, though the results provide important context to an ongoing restoration project at the JLDP. Increased vegetation cover is hypothesized to have stabilized the dunes which limits aeolian activity, sediment transport from the northern source beach to downwind southern beach, and related ecological processes. The purpose of this work is to map and calculate areal and percent surface cover changes in vegetation, bare sand, and infrastructure from 1929 to 2023. Aerial images were georeferenced to selected ground control points for comparison of surface classifications over time. Each image surface classification was trained in ArcGIS Pro using 30 samples for each surface type. Pixels were classified using the Image Classification tool where a supervised classification was run for each image. Faulty pixels were manually corrected and change detection maps were generated using the Raster Calculator. The results of this work provide insight to the current and historical stability trends of the HBDS. These results are important to inform the efforts of a dynamic dune restoration at the JLDP, as knowledge of past dune mobility can provide context for current restoration performance and goal expectations.</p>

Keywords: restoration, coastal, GIS, dunes, headland bypass dune system, surface classification

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