While it is commonly believed that wildfires primarily drive the transformation of sagebrush ecosystems, a recent study reveals that the invasion and domination of native plant communities by annual grasses often progresses independently of wildfire.
The research team from USDA’s Agricultural Research Service (ARS) and Working Lands for Wildlife-affiliated researchers at the University of Montana found almost 80% of the grasslands in the Great Basin that have transitioned to the dominance of invasive grasses have done so without burning in the preceding 10 years.
“We found that wildfire is not the predominant driver of invasive annual grass expansion in the Great Basin, but it is still a major issue that can promote annual grass abundance and negatively impact a wide variety of ecosystem services and values ranging from forage for cattle production to sagebrush obligate wildlife habitat,” said Chad Boyd, co-author and research leader at the USDA ARS Range and Meadow Forage Management Research Unit. “However, annual grass management focused solely on wildfire suppression and post-fire restoration is unlikely to reverse widespread conversion to invasive annual grasses.”
In the West, invasive annual grasses like cheatgrass, ventenata and medusahead are causing trouble in sagebrush habitat. The Great Basin is feeling the impact as these invasive grasses reduce plant diversity, disrupt nutrient cycles and harm the habitat for wildlife dependent on sagebrush.
The study—published in the journal Biological Conservation—using data from the Rangeland Analysis Platform and on-the-ground surveys focused on lands managed by the Bureau of Land Management (BLM) in the Great Basin, reveals a trend: the production of invasive grasses has tripled since the early 1990s.
Historically, the sagebrush ecosystem had sparse understories and infrequent wildfires. However, invasive annual grasses have changed this landscape, increasing the risk of fires and making the recovery of sagebrush shrubs a lengthy process spanning decades.
From 1994 to 2020, a vast area of the Great Basin, equivalent to 12 times the size of Yellowstone National Park, transitioned to annual grass dominance. Notably, 77% of this transition occurred without burning in the previous decade, suggesting that fire is not necessary for these transitions.
The study suggests that efforts solely focused on wildfire suppression and post-fire rehabilitation won’t effectively slow the expansion of invasive annual grasses. Shifting from a reactive to a proactive approach, researchers are developing strategies to manage invasive annual grasses directly. Using new remote sensing-derived vegetation datasets, these strategies focus on products that empower managers to deliver interventions where they are most needed.
Proactive management strategies, such as the Defend the Core approach, aim to protect intact sagebrush cores from invasion by enhancing resistance and managing annual grass seed pressure. Promising interventions include new pre-emergent herbicides that suppress annual grasses for multiple years and adaptations in livestock grazing timing to fall and winter, which can reduce cover and density of annual grasses.
The study concludes that fire will continue to be a dominant factor impacting plant communities and the safety and economic well-being of the community.
“As such, there is a long and growing list of reasons why management of fire and fuels should remain a cornerstone of efforts to conserve sagebrush ecosystems,” the study read. “However, our analyses make clear that managing fire is not the same as managing annual grasses, and neglecting the latter will only compound the challenges of the former.”
Shifting from reactive fire-focused strategies to proactive management targeting invasive grasses is crucial to developing effective conservation and management plans for the sagebrush ecosystem. — Charles Wallace, WLJ contributing editor
