Wildlands that border Arizona's scenic Upper San Pedro River are covered with hardy grasses and rugged desert shrubs. But hungry cattle could easily overgraze these tasty, nutritious plants. In turn, overgrazing can lead to flooding and erosion.

To prevent that from happening, scientists at the Southwest Watershed Research Center at Tucson, Ariz., are readying a new, computer-based aid that the region's ranchers, wildlife managers and other specialists can use to safeguard this ecosystem. The researchers' invention converts — into numerical form — details about the rangelands. This information comes from satellite imagery, weather records and studies of how rangeland plants grow. The Tucson center is part of the Agricultural Research Service.