Variables influencing law enforcement off-road route proliferation on an arid site

Off-road vehicle impacts are a common and often severe form of disturbance in arid and semiarid lands around the world. Determining the underlying impetus behind the generation of new routes may allow better management of their impacts. We hypothesized that six variables may have predictive power: distance from slopes greater than 34% (impassible slopes), distance from unauthorized routes, slope, view from authorized routes (driving to places that cannot be seen), distance from authorized routes, and elevation. Route proliferation in the San Cristobal Valley, Arizona, USA, a site with border enforcement travel but without recreational use, was measured using remotely sensed imagery and 7014 km of unauthorized routes were identified. Two variables were significant (p<0.05, R²=0.57) predictors of route proliferation: distance from slopes greater than 34% and distance from unauthorized routes. For each kilometer distant from the slope, route density decreased by a factor of two and, for each 100 m distant from unauthorized routes, route density decreased by a factor of five. Slope, view from authorized routes, distance from authorized routes, and elevation were also tested but were not significant and were not included in the model. Unauthorized route density appears at least partially predictable and analysis of geographic variables may offer a way to prioritize route management decisions.