Sagebrush (Artemisia species) habitat, an intricate, species-rich mosaic of different sagebrush species and a remarkably diverse assemblage of grasses, forbs, and other shrubs, once covered about 170 million acres (69 million ha) across the Western United States (fig. 4.3.1). Noss et al. (1995) note that sagebrush habitat is an imperiled ecosystem because of its degradation, fragmentation, or removal by humans (Connelly et al. 2011), including conversion to agriculture (Leonard et al. 2000) compounded by other factors such as invasion by nonnative annual grasses, encroachment by junipers and piñon pines, improper grazing, and climate change (Davies et al. 2011) that interact in complex ways (see Finch et al. 2015). Additional discussion about climate impacts on sagebrush rangelands can be found in Chapter 6.1 (Wright, this synthesis, Ecological Disturbance in the Context of a Changing Climate: Implications for Land Management in Northeastern California).