Relationships between Salt Marsh Vegetation and Surface Elevation in Coos Bay Estuary, Oregon

Abstract

Salt marsh habitats support a diverse array of estuarine species but are vulnerable to increased inundation resulting from sea-level rise. In order to characterize relationships between vegetation and elevation and inform assessments of risk to salt marsh communities from projected sea-level rise, we collected vegetation and elevation data at 42 salt marsh sites in Coos Bay Estuary, Oregon. For 1-m2 plots along transects from the bayside edge to the upland, we recorded height and percent cover of all plant species present. We determined plot location and elevation at 1-m intervals with a Trimble Pathfinder Pro XRS differential GPS and TOPCON GTS223 Total Station for comparison with existing LiDAR. Cluster analysis distinguished six vegetation groups. Two low marsh groups (average elevation 1.74 and 1.91 m) were characterized by swampfire (Sarcocornia perennis) with an average height of 31 cm, and saltgrass (Distichlis spicata) with an average height of 22 cm. Plots in the high marsh groups had average elevations ranging from 2.21 to 2.57 m and were characterized by tufted hairgrass (Deschampsia cespitosa) and Oregon gumweed (Grindelia stricta var. stricta), with an average height of 50 cm and 43 cm, respectively. Mid-marsh groups (average elevations of 2.01 and 1.99 m) were dominated by Lyngbye's sedge (Carex lyngbyei) with an average height of 64 cm. The data collected along these transects allowed us to assess LiDAR elevation accuracy, identify sites where LiDAR data require correction, and provide species-specific height data for correction of LiDAR in areas of dense vegetation.