Shrubs are the cornerstones of arid ecosystems in the West, mitigating soil erosion, fostering plant and animal biodiversity, storing carbon, and providing cover and forage for wildlife, such as the greater sage-grouse's recent addition to the candidate list of threatened species. These shrub-dominated ecosystems are being compromised, however, by increased fire frequency and size, coupled with encroachment of invasive plants. Subsequently, post-fire restoration has become a fundamental component for maintaining ecosystem function and resiliency in these shrublands.
Many of the restoration plantings currently used in the Intermountain West include big sagebrush seed collected from naturally occurring populations. In addition, increased wildfire frequency and the introduction of invasive annual grasses in the Mojave and Colorado Plateau have increased the need to restore blackbrush ecosystems. Shrubland restoration through wildland plantings is most effective when the plant materials used are site-adapted and have appropriate levels of genetic diversity promoting resilient ecosystems, now and in the future. Moving plant materials responsibly requires knowledge of how plant populations and species are adapted across variable environments.
Studies in which plants representing multiple populations of a single species are grown together in common environments provide a useful approach for ascertaining species limits. Two common gardens have been established for big sagebrush and blackbrush at the Great Basin and Desert Experimental Ranges in Utah, respectively. These experimental areas are ideal for these studies because of shrub-dominated naturally occurring vegetation, historical and ongoing weather data collection, and protection from livestock use.
To date, dramatic differences have been observed among big sagebrush and blackbrush populations in the experimental ranges' common gardens. For both species, mortality has varied from 0 to 100 percent after 3 years. In the case of blackbrush, DNA (deoxyribonucleic acid) data support common garden observations made by researchers, which suggests that this species has two ecotypes or metapopulations that group geographically to the Mojave Desert and Colorado Plateau regions. For example, mortality of Mojave plants at the Desert Experimental Range, which climatically resembles the colder Colorado Plateau, reached nearly 90 percent after a recent, unusually cold winter when compared with the 20-percent mortality rate for Colorado Plateau plants. These results help land managers make prudent, research-based decisions on seed transfer protocols in the event of climate change.