Fragmentation and Loss: A GIS View of the Mojave Desert Tortoise Habitat

Landscapes are ever changing or being changed by natural forces or by human activities. The changes, over time, frequently result in more complex and fragmented landscape structures. Much of the fragmentation is due to human activities, primarily roads. Landscape indices, tools that identify and quantify landscape structure, provide statistical analysis of how the landscape is fragmented by roads and what, if any, habitat loss resulting from road-avoidance behavior might be present. The interpretation of the landscape indices can give scientists clues to where limited resources can be directed to preserve the habitat. The desert tortoise habitat was chosen as the subject for a baseline assessment of fragmentation and habitat loss in theMojave Desert. The desert tortoise is highly sensitive to changes in its environment. In 1990, the tortoise was listed as Threatened due to dramatic decreases in its population over only a few decades. The reasons for the listing included deterioration and loss of habitat. The desert tortoise continues to be studied for changes in population that might indicate broader problems for all species in theMojave Desert. This project involved the statistical analysis of the desert tortoise habitat, using Patch Analyst 3.1, a landscape analysis program incorporating landscape indices, ArcView 3.3, and ArcGIS 9.1 to model the desert tortoise habitat and provide a baseline assessment of fragmentation due to roads and potential for habitat loss resulting from road-avoidance behavior in the desert tortoise habitat. Preliminary analysis of the landscape-level statistics suggests that the Mojave Desert is highly fragmented, particularly in the western Mojave Desert of California. Roads, particularly highways and secondary roads impose significant barriers to movement, although how this might affect the desert tortoise, with its small home range, remains to be determined. The evidence of greater road-avoidance distances based on the figures from a von Seckendorff Hoff and Marlowe (2002) study, produced evidence of loss of habitat, especially for near highways and secondary roads. Overall, it appears that the Mojave Desert tortoise habitat is extremely fragmented, with large potential for significant habitat loss resulting from the human need for more roads