Sagebrush Shrub-steppe or Cheatgrass Prairie?

Although I work in irrigated agriculture, the views on my morning commute are all sagebrush, or the shrub-steppe as this native plant community is called. And cheatgrass, a lot of cheatgrass. Where there have been recent fires, stands of cheatgrass thrive. Sagebrush, the iconic plant of the shrub-steppe ecosystem, is having a hard time. The combined effects of fire frequency, climate change, and cheatgrass invasion have made sagebrush recovery an uphill battle. Will the shrub-steppe recover to its former subtle beauty, or should we get used to the cheatgrass prairie?

Sagebrush with mountains in the background
The shrub-steppe is in danger of becoming a cheatgrass prairie. It is estimated that only 12% of functional shrub-steppe habitat remains in Washington state. Licensed through Adobe Stock.

Cheatgrass Invasion

Map of the US with green highlighted counties
Figure 1. Cheatgrass is found in every US state. However, it is in the arid West that is the biggest problem. Map from EDDMaps.

The most serious threat to sagebrush recovery is the invasion of cheatgrass. Although the beauty of the shrub-steppe sagebrush is subtle, cheatgrass is ugly in comparison. Sagebrush smells wonderful after a rain. Cheatgrass seeds get in your socks. And cheatgrass is devious; putting your socks through the laundry does not kill the seeds (Lefcort and Lefcort, 2014). And its mean; cheatgrass out-competes native vegetation by using water and nutrients before native plants can (Archer et al., 2023). But there’s a worse effect than the grass and its seeds; fire.

Fire Frequency

Fire has always been a part of the natural cycle in the Western US. However, in recent decades, fire frequency has increased significantly, partly due to a combination of climate change, human activities, and cheatgrass or other invasive species. Cheatgrass has a shorter life cycle than most native plant species, especially perennials, allowing it to establish quickly after a fire and out-compete sagebrush seedlings. The early growth then dies quickly, increasing the fuel load and making the system more prone to frequent fires. With more frequent fires, sagebrush struggles to reestablish between successive burn events (Pilliod et al., 2021). This vicious cycle can end with cheatgrass forming dense near-monocultures, all but eliminating the chance of sagebrush recovery.

Habitat Loss

The resulting cheatgrass prairie is an impoverished habitat. Species like the Columbia Basin pygmy rabbit, already in danger because of habitat loss from land use change, could be put further at risk by loss of sagebrush habitat to cheatgrass. Other species, too, rely on the shrub-steppe environment. It could be a coincidence, but the marmots that I looked for every morning in a roadside rock pile (yes, marmots that live in the sagebrush) disappeared after a fire went through the area.

Climate Change

Climate change adds other challenges to the process of sagebrush recovery. Rising temperatures and changing precipitation patterns can lead to drier conditions, making it harder for sagebrush to establish and survive. Changes in the timing and intensity of rainfall can affect seed germination and the availability of water during critical growth periods. And increased evaporation rates can further dry the soil, hindering the growth of young sagebrush seedlings.

Recovery Timeline

The recovery timeline for sagebrush after a fire can vary significantly depending on several factors. Sometimes, sagebrush can resprout from underground buds or surviving root systems, leading to relatively quick recovery. However, if the fire is severe and kills the above-ground vegetation, sagebrush relies on seed germination to regenerate, which is a slower process. Under ideal conditions, it can take several years for sagebrush to reestablish, and in some cases, decades are required for the ecosystem to fully recover. With cheatgrass, hotter, drier weather, and more frequent fires, by some estimates it may take up to 80 years for the sagebrush to recover fully (Zaiats et al., 2023). Or it may never recover, at least not without some intervention on our part.

Human Intervention

While sagebrush has the capacity for natural recovery, human intervention can play a crucial role in aiding the process. Efforts such as reseeding with native sagebrush species, implementing strategic grazing management, and controlling invasive species can help restore the shrub-steppe. These restoration efforts must then be protected from fires or they will be wasted (Pilliod et al., 2021; Young and Clements, 2009).

“Once cheatgrass occupies a site, it retains its role indefinitely without extensive control measures,” Mack, 2011

Given the factors favoring cheatgrass establishment and the fact that cheatgrass has already established on so many acres across the Western US, the outlook is not good. Over 60 years of attempts to control the species have failed: tillage, herbicides, and seeding competitive species (native and non-natives). Biocontrol remains the one hope, but here again, there have been many failures. Cheatgrass-specific herbivore insects are not a good option as there are both native and introduced Bromus species that would probably also be affected. Fungi and bacteria may provide a better strategy, but so far, no breakthroughs. Restoration of soil biological crusts can stop or slow cheatgrass invasion, but as with the plants of the shrub-steppe, take many decades to get to this point. In a review of the topic, Mack (2011) concludes that without an effective biocontrol agent, the “cheatgrass juggernaut” is unstoppable.

Table of management strategies
A range of management strategies depending on the level of cheatgrass infestation. Table 4-2 from the Cheatgrass Management Handbook, University of Wyoming and Colorado State University.

Cheatgrass Prairies?

Really, I’d like to give some signs of hope. However, the future of the shrub-steppe is bleak, especially on private lands where low economic returns from the land prohibit investments in restoration of the sagebrush. What does this mean? More fires. Fewer native animals and insects, including those that help with pest management in nearby cropland (James et al., 2018). Given the current trajectory, we will have to get used to cheatgrass prairies.

References

Archer, D., D. Toledo, D.M. Blumenthal, J. Derner, C. Boyd, et al. 2023. Invasive annual grasses—Reenvisioning approaches in a changing climate. Journal of Soil and Water Conservation 78(2): 95–103. doi: 10.2489/jswc.2023.00074.

James, D.G., L. Seymour, G. Lauby, and K. Buckley. 2018. Identity and Seasonal Abundance of Beneficial Arthropods Associated with Big Sagebrush (Artemisia tridentata) in Central Washington State, USA. Insects 9(3): 76. doi: 10.3390/insects9030076.

Lefcort, H., and C. Lefcort. 2014. Cheatgrass (Bromus Tectorum) Seeds are Still Viable after Laundry Cycle. naar 34(4): 505–508. doi: 10.3375/043.034.0413.

Mack, R.N. 2011. Fifty years of ‘waging war on cheatgrass’: research advances, while meaningful control languishes. Fifty years of invasion ecology: the legacy of Charles Elton. Oxford, UK: Wiley-Blackwell: 253–265.

Pilliod, D.S., M.I. Jeffries, J.L. Welty, and R.S. Arkle. 2021. Protecting restoration investments from the cheatgrass-fire cycle in sagebrush steppe. Conservation Science and Practice 3(10): e508. doi: 10.1111/csp2.508.

Young, J., and C.D. Clements. 2009. Cheatgrass: Fire and Forage on the Range. University of Nevada Press.

Zaiats, A., M.E. Cattau, D.S. Pilliod, R. Liu, J.M. Requena-Mullor, et al. 2023. Forecasting natural regeneration of sagebrush after wildfires using population models and spatial matching. Landsc Ecol 38(5): 1291–1306. doi: 10.1007/s10980-023-01621-1.