26th Annual Meeting and Symposium of the
Desert Tortoise Council, March 16-18, 2001
Abstracts

POSTER

Using GIS to Model Desert Tortoise Habitat in Southwestern Arizona

Betsy Wirt¹, Nancey Favour², Tom Potter³, Ken Lee⁴, and Carnell Council II^4
1Luke Air Force Base, 56 RMO/ESMN, 6605 North 140th Drive, Luke, AFB 85309
²Organ Pipe Cactus National Monument
³US Forest Service; ⁴BTG Inc. AES

Southwestern Arizona has large parcels of land managed by a variety of Federal Agencies with few natural resource management personnel. Limited time and resources for agency biologists are common complaints. Having a realistic model of desert tortoise habitat provides a valuable reference for protecting desert tortoises while also planning new projects and prioritizing management activities. Using GIS, we developed a model of tortoise habitat in Organ Pipe Cactus National Monument and the Barry M. Goldwater Range in southwestern Arizona. Data layers for the model include vegetation (paloverde-cacti-mixed scrub series), elevation (greater than 300M and less than 1067m) and slope (less than 70 %). Potential tortoise habitat required all three qualifiers be met, otherwise the area was considered non-potential tortoise habitat. Potential habitat areas were further divided into high quality and low quality tortoise habitat by trying to capture potential sheltersite areas. Buffering 20 meters on washes from the USGS 7.5' hydrography theme created an estimator for caliche cavities, creating the potential sheltersites qualifier. We attempted to test the model using frequency of tortoise sign locations found during field surveys that intersected with the habitat model. Observations were identified within the high, low, or unsuitable habitat model classes. The transect data applied to the model shows that it captured most of the habitat appropriately. The model is not perfect and further validation of the model is appropriate, however is a realistic estimate of desert tortoise habitat in this region.