Transportation planning is one of the most significant challenges facing the Bureau of Land Management (BLM) and the National Park Service (NPS) as the agencies develop a management plan for the Arizona Strip Resource Area. The plan for this area is especially critical because it will determine the direction of management for the next twenty years at two of the BLM’s new national monuments — Grand Canyon-Parashant and Vermilion Cliffs. Transportation features such as roads and other routes ensure access for recreation and public safety. But those activities must be balanced against the responsibility to protect the area’s resources — including the wildlife and plant species (many of them imperiled) and geological, archaeological, historic, and cultural attributes that are listed in the proclamations for Grand Canyon-Parashant and Vermilion Cliffs national monuments.
A large body of scientific studies indicates that roads can and do have significant negative effects on resources such as those in the monuments of the Arizona Strip. We completed a spatial analysis of the area to assess the potential effects that two different transportation systems are likely to have on habitat for five wildlife species — the desert tortoise, mountain lion, bighorn sheep, pronghorn, and mule deer. The transportation systems are: (1) the BLM’s Route Inventory, which contains an extensive network of existing and reported routes across the Arizona Strip; and (2) the Conservation Route Proposal, which is the network supported by the Arizona conservation community and developed from an on-the-ground survey of Grand Canyon-Parashant and Vermilion Cliffs.
Among the results:
- The BLM Route Inventory includes approximately 7,524 miles of roads across the Arizona Strip at an average route density between 1 and 2 mi/mi2.
- Under the BLM Route Inventory, only 6 percent of the Arizona Strip and only 10 percent of monument lands are more than 1 mile from a road.
- Findings suggest that the BLM Route Inventory is extensive enough to have substantial negative effects on all five of the selected wildlife species.
- At least 62 percent of desert tortoise habitat in Grand Canyon-Parashant National Monument is within 0.5 miles of a route. Tortoise populations tend to decrease within this parameter.
- From 53 percent to 75 percent of mountain lion habitat has a route density higher than 1 mi/mi2 and/or lies within 0.3 miles of a road — conditions documented as detrimental for mountain lions.
- Twelve percent to 28 percent of all bighorn sheep habitat lies within 0.09 miles to 0.25 miles of a route. Sheep are disturbed by human activity on routes within these parameters.
- At least 55 percent of pronghorn habitat and 41 percent of mule deer habitat are located within 0.25 miles of a route. Pronghorn and deer avoid areas this close to a route and cannot use habitat fully.
- The Conservation Route Proposal, on the other hand, contains 822 miles of routes at an average road density of 0.4 mi/mi2 in the monuments and desert tortoise Areas of Critical Environmental Concern.
- Even under the Conservation Route Proposal, 44 percent of monument land is more than 1 mile from a road, and only 18 percent is more than 2 miles from a road.
- While considerably smaller in relation to road mileage and density than the BLM Route Inventory, the conservation proposal will not provide sufficient habitat for some of the selected wildlife species, desert tortoise in particular.
We urge BLM to model its transportation network on the basic precept of the Conservation Route Proposal: that is, protection of large core areas that will support populations of imperiled and other wildlife species across their range in the Arizona Strip and adjacent lands. Such areas will also serve important purposes in addition to protecting wildlife, such as conserving other resources and wilderness character. Specifically, the transportation plan should:
- Provide large blocks of core habitat more than a mile from a road within desert tortoise habitat.
- Reduce road mileage in mountain lion habitat to densities less than 1 mi/mi2. This would require the closure of many routes in the BLM Route Inventory.
- Reduce road mileage in bighorn sheep, pronghorn, and mule deer habitat to levels in the Conservation Route Proposal so that core habitat areas are more than 0.25 miles from a road. Again, this requires substantial reductions in the routes included in the BLM Route Inventory.
- Use our landscape fragmentation metrics to guide management decisions regarding transportation routes for other wildlife species. Goals are to reduce road density and edge effects and increase core areas to provide greater habitat security.
- Establish priorities and adopt best-practice procedures to close and reclaim roads and other routes.
We also recommend that the BLM incorporate the detailed guidance presented at the end of this report as the agency develops its transportation plan. Essential elements include:
- Generate transportation network scenarios based on directives in the monument proclamations, reliable data, and high-quality analysis.
- Assemble wildlife habitat use information in compliance with agency obligations to use accurate, high-quality scientific information in analyses.
- Generate landscape fragmentation metrics to represent the best available science.
- Integrate the results of analyses into management plan alternatives and use them as the basis for selecting the preferred alternative, as well as for defining a road closure plan, mitigation and adaptive management.