Photo: Sagebrush & Pronghorn Antelope near Pinedale, Wyoming. © 2019 Delena Norris-Tull.
Potential Impacts of Climate Change on Rangelands
Research summary and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, October 2021.
Sheley, Hamerlynck, and Boyd (2017) report that, “Rangelands cover nearly one-half of the Earth’s land surface and provide life sustaining goods and services to about one-third of the global population. Low and variable rainfall combined with often infertile soil make the world’s rangelands highly susceptible to degradation, invasion (by weeds), and global climate change. The inability to establish healthy plant communities is cited by stakeholders as the single largest barrier to implementing restoration and turning the tide against the hundreds of thousands of hectares of sagebrush steppe lost to invasive plants each year. Despite over a century of research, rangeland science lacks a comprehensive understanding of the ecological processes influencing seedling establishment.” [Refer to the section on Rangeland Restoration, within the sections on Innovative Solutions, for a description of the management practices this team of scientists recommends].
Swanson, Sheley, & James (Jan., 2020), carried out a fascinating experiment on the effects of drought on sagebrush steppe habitat. Because “plant reproduction is highly sensitive to stress from severe weather,” they wanted to test the question, “Do shrubs improve reproductive chances of neighbors across soil types in drought?” In an eastern Oregon sagebrush-bunchgrass steppe, they compared the reproductive success of various perennial native bunchgrass species in two different soil types (well drained fine sandy loam, and very cobbly loam), and three moisture regimes (moist, ambient, and drought). They compared areas with Big Sagebrush present with areas with shrubs removed. “Analysis revealed species varied significantly in their response (to shrubs) across treatments… Drought conditions incited the strongest facilitated response among species” (Swanson, et al., 2020).
At the cobbly loam site, “three out of five species were facilitated in drought conditions compared with one out of five species” at the fine sandy loam site. These results suggest that as climate change advances, and drought conditions increase, some native perennial grass species may be more tolerant to the changes, if native sagebrush shrubs are available to provide protection.
“Sagebrush shrubs extract soil moisture at deeper levels than perennial bunchgrasses… and have been shown to increase surface soil moisture… and nitrogen uptake into inflorescences through hydraulic lift” (Swanson, et al., 2020).
“One of the most striking findings in this study is that there was very little variation in response of species across sites in the treatments with the shrub neighbor but significant variation across sites when sagebrush was removed... We propose a possible cause for this result is that shrubs buffer environmental differences across population locales. This finding has important implications, because it supports the notion that shrubs expand the range of a species distribution…and the potential for shrubs to serve as reproductive climate refugia” (Swanson, et al., 2020).
Lars Baker, retired Fremont County, Wyoming, Weed and Pest District Supervisor, pointed out the following: “We have removed nutrients from the soil, over the decades of farming and ranching. So now much of our land is poor for farming. Weeds are the direct result of how humans have disturbed the land. Native sagebrush range developed over thousands of years. Now that we have disturbed it, we cannot restore it simply by stopping irrigation. The problems we have today with cheatgrass are due to the fact that we have caused so much destruction to the ecological systems.
“Wyoming tried to grow dry-land wheat, but there is not enough rainfall for this to be successful. It failed. So now when we plant native grass seed, they often will not grow, because there is no longer enough rainfall.”
- Sheley, R., Hamerlynck, E., Boyd, C. (Project Team). (2017). Project Annual Report. Range and meadow forage management research: Burns, OR. USDA, Agricultural Research Service.
- Swanson, E.K., Sheley, R.L., James, J.J. (Jan., 2020). Do shrubs improve reproductive chances of neighbors across soil types in drought? Oecologia, 192(1): 79-90.