Ecological remote sensing of invasion by perennial pepperweed

Hyperspectral and LiDAR remote sensing have the potential to address a wide variety of ecological questions. We present results of three ecological applications of remote sensing data to study the invasion of the San Francisco Bay/Sacramento-San Joaquin River Delta by Lepidium latifolium (perennial pepperweed). Lepidium is a noxious Eurasian weed aggressively expanding in the western US; understanding the ecology and management options for this weed are priorities. Hyperspectral image data has been used to map Lepidium distributions in several sites of the Bay/Delta annually over 2004-2007. Annual distribution maps allow quantification of Lepidium spread and dispersal: on Bouldin Island, the infestation has increased by 50% in three years; new patches were detected as far as 500m from preexisting ones. We have generated habitat distribution/susceptibility models for Lepidium at the Rush Ranch Open Space Preserve with data extracted from the hyperspectral distribution maps and environmental variables derived from hyperspectral and LiDAR datasets. This analysis found that Lepidium occurrence at this site is primarily a function of the distances from a channel and the upland-marshland margin. Finally, hyperspectral datasets of Rush Ranch and Cosumnes River Preserve revealed substantial spatiotemporal variation in Lepidium phenology. Variables extracted from the remote sensing datasets explained 33-56% of the spatial variation in phenology at these sites and interannual phenologic differences at the Cosumnes River Preserve were closely related to hydrology. Our results highlight the importance of microtopography and water availability to Lepidium distribution and phenology, increasing our understanding of this invasive species and informing better management