Use of lidar to study changes associated with Spartina invasion in San Francisco Bay marshes

Extensive alteration of the tidal salt marshes of San Francisco Bay has created an urgent need to preserve the few remaining areas of relatively pristine tidal marshes. The dynamics of these marshes can be quantified and mapped using the high vertical and horizontal point density of airborne laser scanners (lidar) if their data quality is adequate. We evaluated lidar's ability to characterize wetland topography and vegetation structure, with emphasis on measuring short-term changes associated with the invasive Spartina. Measurable errors between flight lines and between laser returns were observed. By comparing lidar datasets with ground measurements we found that lidar did not reach the ground underneath vegetation. Nonetheless, change detection using digital surface models showed that Spartina markedly affected the accretion–erosion patterns of the shoreline and the water drainage patterns on the mudflat. With some exceptions, Spartina patches showed evident expansion patterns with rates of up to 2.5 m/year. Our study indicates that lidar has a great potential to discriminate Spartina species and marsh components, and to quantify sediment dynamics associated with the Spartina invasion, and changes in Spartina structure and biomass.