Humans have dramatically altered wildlands in the western United States over the past 100 years by using these lands and the resources they provide. Anthropogenic changes to the landscape, such as urban expansion and development of rural areas, influence the number and kinds of plants and wildlife that remain. In addition, western ecosystems are also affected by roads, powerlines, and other networks and land uses necessary to maintain human populations. The cumulative impacts of human presence and actions on a landscape are called the “human footprint.” These impacts may affect plants and wildlife by increasing the number of synanthropic (species that benefit from human activities) bird and mammal predators and facilitating their movements through the landscape or by creating unsuitable habitats. These actions can impact plants and wildlife to such an extent that the persistence of populations or entire species is questionable.
The human footprint map focuses on shrubland ecosystems and combines models of habitat use by synanthropic predators (“top-down” effects) and the risk of invasive plant presence (“bottom-up” effects) to estimate the total influence of human activities. Humans have dramatically altered wildlands in the western United States over the past 100 years by using these lands and the resources they provide. Anthropogenic changes to the landscape, such as urban expansion, construction of roads, power lines, and other networks and land uses necessary to maintain human populations influence the number and kinds of plants and wildlife that remain.
We developed the map of the human footprint for the western United States from an analysis of 14 landscape structure and anthropogenic features: human habitation, interstate highways, federal and state highways, secondary roads, railroads, irrigation canals, power lines, linear feature densities, agricultural land, campgrounds, highway rest stops, land fills, oil and gas development, and human induced fires. We used these input layers to develop seven models to estimate the total influence of the human footprint. These models either explored how anthropogenic features influence wildlife populations via changes in habitat (road-induced dispersal of invasive plants, oil and gas developments, human induced fires, and anthropogenic habitat fragmentation) or predators densities (spatial distribution of domestic and synanthropic avian predators). The human footprint map is a composite of these seven models. The final map consists of a 180 meter resolution raster data set with 10 human footprint classes.
Modeling the human footprint across large landscapes also allows researchers to generate hypotheses about ecosystem change and to conduct studies in regions differing in potential impact. Because funding for restoration and conservation projects is limited, and because there is little room for errors in the management of species of concern, land managers are able to maximize restoration and conservation efforts in areas minimally influenced by the human footprint. As such, the human footprint model is an important first step toward understanding the synergistic effects acting on shrublands in the western United States.
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