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Contributed Talk

Session: : Invasion: Dynamics, Population Processes

COS 87-6 - Fire needs annual grasses more than annual grasses need fire.

Tuesday, August 8, 2023
11:15 AM – 11:30 AM PDT
Location: E142
Abstract: Rapidly expanding invasive annual grasses pose an urgent threat to sagebrush ecosystems of western North America where they displace keystone shrubs, alter natural fire regimes, and fuel catastrophic wildfires. The accelerating loss and degradation of sagebrush ecosystems resulting from positive feedbacks between invasive annual grasses and fire is increasingly seen as an existential threat to sagebrush obligate wildlife such as sage-grouse, yet halting this ecosystem transformation has vexed managers for decades. Using dynamic, remotely-sensed rangeland vegetation data, we track the 8-fold expansion of invasive annual grass dominance over the past 3 decades in the US Great Basin, highlighting the recent movement into higher elevations and north-facing aspects previously considered unlikely to experience such transitions. We then use remote sensing-derived wildfire perimeter and burn severity datasets to explore the role of fire in transitions to annual grass dominance. Although annual grasses and wildfire are so tightly associated that one is rarely mentioned without the other, our findings reveal widespread transformation of sagebrush ecosystems by invasive annual grasses in the absence of fire. These findings are discussed in the context of strategic management; we argue a pivot from primarily reactive management (e.g., fire suppression and post-fire restoration in heavily-infested areas) to proactive management (e.g., enhancing resistance and managing propagule pressure in minimally-invaded areas) is urgently needed to slow or reverse the loss of Great Basin sagebrush ecosystems.