Type: report

Article abstract: Vernal pools are seasonal, depression-type wetlands which function as micro-habitats that support multiple rare, threatened and endangered species. Vernal pools largely occur on tops of mesas within the western half of San Diego County. Due to decades of expansive urban development, only 5% of the original vernal pool population exists today and many of the remaining pools are severely degraded and are at risk of being destroyed. Vernal pools are now considered sufficiently critical that local, state and federal laws require the protection of vernal pools even when they occur on private property. Successful stewardship of vernal pools is dependent on the ability to locate and monitor the status of the pools and the species that occur within them. Currently, the management and monitoring of vernal pools is performed through field surveys which is time consuming, costly, and limited in spatial coverage. Remote sensing offers the opportunity to derive valuable habitat information at spatial and temporal scales that are not possible with ground sampling. The utility of high spatial resolution, multispectral imagery was evaluated for multiple tasks associated with vernal pool mapping and characterization, including: locating unknown pools and delineating pool basin extents, mapping vernal pool plants, estimating pool depth, and characterizing land use and land cover adjacent to sensitive vernal pool habitats. ADAR 5500 multispectral imagery was acquired at multiple resolutions within two San Diego County study sites during February and May of 2001. The first site at Otay Mesa was reconstructed in 1998 as part of a land mitigation project and contains over 300 vernal pools within a small geographic area. Naturally occurring pools in this area were scraped and destroyed in the 1970s. The second site at Marron Valley contains a small number of naturally occurring vernal pools. This site is the subject of biological monitoring, as recent fires and many years of cattle grazing have degraded the habitat surrounding the vernal pools. An experiment was performed with multiple resolutions of imagery at both study sites to determine to optimum spatial resolution for identifying and delineating vernal pools. One foot resolution image mosaics at each site were aggregated to simulate 2 ft, 4 ft, 8 ft, and 16 ft spatial resolutions. Nine interpreters visually identified apparent vernal pools beginning with the lowest resolution imagery and then with progressively higher sp