IDENTIFYING SPECIES HABITATS IN ARID SETTINGS USING REMOTE SENSING AND GEOMORPHIC ATTRIBUTES

The desert southwestern United States hosts habitats for several threatened and endangered species. One of these is the desert tortoise (Gopherus agassizii), which is found throughout the Mojave and Sonoran Deserts. In this application of remote sensing and geology, we use a combination of technology and ground-based surveys to determine the potential to predict potential habitats. Remote sensing would be especially useful in the large and remote land areas inhabited by these tortoises and the substantial variability of attributes that are favorable for habitats (shrub canopies of specific volume and area, presence of ledges, etc.). In this study, which takes place in the Boulder City (Nevada) Conversation Easement area (~35,500 hectares), we compare airborne Lidar data and color infrared imagery (CIR) to field measurements, including known tortoise habitats. Vegetation metrics using Lidar (5-7 points/m²) and CIR imagery (15 cm pixels) across the entire field area include percent cover, shrub height and area, NDVI, and the presence/absence of (topographic) ledges greater than 50 degrees. Field surveys, including the use of 1280 line transects (16 transects at each of 80 field plots undertaken in an earlier study) obtained information on percent ground cover, and species richness of perennial and ephemeral plant species. We then overlay these attributes atop digital soil maps and known locations of tortoise burrows, allowing us to create a predictive model of potential tortoise habitats. Results showed that the percent ground cover ranged from 5% on the distal/proximal portions of the alluvial fan to 25% on the mid-fan portions. Observed tortoise burrows are concentrated in areas with denser vegetation on relatively soil stable, mid-fan locations, with several located within or adjacent to ephemeral channels. Ongoing field surveys will provide data for further statistical analyses, but existing results indicate that the lidar data and CIR imagery created an effective digital representation of the desert ecosystem, which can be used for a variety of ecological and geological studies, including habitat assessment.