The human footprint in the west: A large-scale analysis of anthropogenic impacts

Anthropogenic features such as urbanization, roads, and power lines, are increasing in western United States landscapes in response to rapidly growing human populations. However, their spatial effects have not been evaluated. Our goal was to model the human footprint across the western United States. We. rst delineated the actual area occupied by anthropogenic features, the physical effect area. Next, we developed the human footprint model based on the ecological effect area, the zone in. uenced by features beyond their physical presence, by combining seven input models: three models quanti. ed top- down anthropogenic in. uences of synanthropic predators ( avian predators, domestic dog and cat presence risk), and four models quanti. ed bottom- up anthropogenic in. uences on habitat ( invasion of exotic plants, human- caused. res, energy extraction, and anthropogenic wildland fragmentation). Using independent bird population data, we found bird abundance of four synanthropic species to correlate positively with human footprint intensity and negatively for three of the six species in. uenced by habitat fragmentation. We then evaluated the extent of the human footprint in relation to terrestrial ( ecoregions) and aquatic systems ( major rivers and lakes), regional management and conservation status, physical environment, and temporal changes in human actions. The physical effect area of anthropogenic features covered 13% of the western United States with agricultural land ( 9.8%) being most dominant. High- intensity human footprint areas ( class 8 - 10) overlapped highly productive low- elevation private landholdings and covered 7% of the western United States compared to 48% for lowintensity areas ( class 1 - 3), which were con. ned to low- productivity high- elevation federal landholdings. Areas within 1 km of rivers were more affected by the human footprint compared to lakes. Percentage human population growth was higher in low- intensity human footprint areas. The disproportional regional effects of the human footprint on landscapes in the western United States create a challenge to management of ecosystems and wildlife populations. Using footprint models, managers can plan land use actions, develop restoration scenarios, and identify areas of high conservation value at local landscapes within a regional context. Moreover, human footprint models serve as a tool to stratify landscapes for studies investigating. oral and faunal response to human disturbance intensity gradients.