Spatiotemporal mapping the usable space of free‐roaming equids across the western United States

Abstract Management of feral equids in the American West is hindered by the lack of a formal habitat map and monitoring system. To address this shortcoming, we developed a method based on annual metrics of water accessibility and forage availability to map the dynamic rangelands where free‐roaming equids (FRE) are found in the western United States. Usable space, defined here as an area that provides the necessary forage and water to sustain a population of free‐roaming equids annually, was mapped for the Bureau of Land Management (BLM) administered Herd Management Areas (HMA), an area covering 107,434 km 2 across 10 western states. We ranked usable space in 3 simple categories representing low, moderate, and high‐quality habitats annually during 1984–2021. The resulting maps displayed a high temporal correlation with the FRE locations derived from aerial population surveys conducted by BLM at triennial intervals across the distribution of FRE. Resultant maps can be used for monitoring changes in habitat, and detection of degradation/enhancement for each individual HMA on an annual basis. Lastly, we ranked mapping units based on their resilience to changes in precipitation and, therefore, the ability to maintain greater proportions of high‐quality habitats through time. From high to low, rankings for HMAs that retained the most high‐quality usable space were found in Nevada, New Mexico, Arizona, and California, whereas most of the low‐quality rankings were found in Oregon and Idaho. The approach described herein has utility for planning aerial surveys, establishing long‐term range monitoring stations, identifying areas for manipulating water availability, or siting habitat restoration activities.