Anthropogenic impacts of restoration and wildfire on sagebrush distribution

Historically, vast areas of cold desert in the Western United States were defined by the abundance of one keystone plant species: sagebrush. The iconic sagebrush plant with its aromatic greenish-gray leaves and gnarled woody trunk provides a range of ecosystem services. For example, sagebrush is the main food source for the West’s unique wildlife species, including sage grouse and pygmy rabbits.

The big sagebrush (left) dominates vast stretches of iconic landscapes in Western North America (right). Photo by Dr. Trevor Caughlin.

Despite their importance, sagebrush plants are disappearing from western landscapes, threatened by wildfires, invasive species, and urban growth. To curb the degradation of this imperiled ecosystem, land managers have spent hundreds of millions of dollars to restore sagebrush populations across their historic range in the Great Basin. The threats to sagebrush ecosystems raise the question of how sensitive sagebrush cover is to human impacts, both positive and negative. Answering this question is complicated by the enormous range of environmental conditions in the Great Basin, from Badwater Basin, the lowest point in North America, to Mount Whitney, the tallest mountain in the contiguous United States. Across the range of natural variation in the Great Basin, how important are human impacts for sagebrush?

Our new paper addresess the question of how human impacts have altered the distribution of sagebrush plants across >200,000 square miles of western land. In collaboration with agency partners at the United States Geological Survey, we assembled a record of data on sagebrush plants, fire history, and restoration treatments spanning nearly 30 years. We then applied mapping and mathematical models to tease apart the importance of wildfire and restoration from climate and topography. We found that wildfire history had negative impacts on sagebrush comparable to the effects of geographic variation in elevation, rainfall, and temperature. This result emphasizes the threat that changing wildfire frequency pose to ecosystem health in the Western United States.

At the same time, we found cause for hope. Restoration action can have a positive impact on sagebrush ecosystems. This was a surprising result, because the 35-year record of restoration treatments included a very wide range of management actions, from planting seedlings to invasive species removal. Altogether, these results point the way for models and mapping to inform conservation of an imperiled habitat.

The modeling approach provided by the researchers is applicable across a range of ecosystems and species. As human impact on nature grows, land managers need reliable methods to guide species conservation and ecological restoration in the face of global change threats. For example, fire frequency is increasingly altered by environmental change in the Great Basin, where millions of acres of public rangelands have been actively managed over the last 75 years. Similarly, a number of international initiatives have set targets to restore ecosystems to hundreds of millions of acres of degraded land worldwide. We demonstrate how documenting decades of land management history can help scientists understand human impacts on ecosystems.

Requena‐Mullor, J. M., K. C. Maguire, D. J. Shinneman, and T. T. Caughlin. (In Press). Integrating anthropogenic factors into regional-scale species distribution models — a novel application in the imperiled sagebrush biome. Global Change Biology.