The Relationship between Vegetation and Topographic Patterns in Coastal Dunes from LiDAR and Optical Remote Sensing

Abstract:

Vegetation plays a key role in barrier islands dynamics by moderating the effects of storms and sea level through sand stabilization and trapping. Vegetation establishment and growth are qualitatively known to depend on environmental factors that vary with elevation and distance from the shoreline, but we lack an adequate characterization of the spatial distribution of barrier island vegetation in relation to topographic determinants. In this study, we develop and apply remote sensing techniques to extend local field observations to larger scales and explore the relations between vegetation density and topography. We use hyperspectral and Lidar data from Hog Island (VA) to address the following questions: 1) Can we map dune vegetation species and density distributions using hyperspectral remote sensing? 2) Can we use LiDAR data to estimate canopy properties (Leaf Area Index, LAI)?, and 3) What are the relations between vegetation presence and topographic properties as they result from two-way ecogeomorphic interactions? Our results show that whereas mapping dune vegetation species using hyperspectral remote sensing is challenging, optical and LiDAR data can be successfully used to characterize overall vegetation density. A comparison between LAI and NDVI (Normalized Difference Vegetation Index), both estimated from remote sensing data, shows a coherent relationship and the spatial distributions of estimated LAI and NDVI agree with the fractional vegetation cover observed in the field. The results also suggest that cover density increases with distance from the shoreline. In the foredune area, vegetation is more sparse than other areas while it is densest on the back side of dunes. Analysis of NDVI and LAI from remote sensing observations can thus provide characterizations of topography and vegetation properties at the island scale, which will assist in shedding light on the interactions between vegetation and sediment dynamics that give rise to coastal dune systems.