Fire needs annual grasses more than annual grasses need fire

Authors: SMITH, JOSEPH - University Of Montana; ALLRED, BRADY - University Of Montana; Boyd, Chad; Davies, Kirk; KLEINHESSELINK, ANDREW - University Of Montana; MORFORD, SCOTT - University Of Montana; NAUGLE, DAVID - University Of Montana

Submitted to: Biological Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2023
Publication Date: 9/23/2023
Citation: Smith, J.T., Allred, B.W., Boyd, C.S., Davies, K.W., Kleinhesselink, A.R., Morford, S.L., Naugle, D.E. 2023. Fire needs annual grasses more than annual grasses need fire. Biological Conservation. 286. Article 110299. https://doi.org/10.1016/j.biocon.2023.110299.
DOI: https://doi.org/10.1016/j.biocon.2023.110299

Interpretive Summary: Invasive annual grasses have degraded rangelands in the western U.S. Over 200,000 ha in the Great Basin are transitioning to annual grasslands annually. The transition from perennial to annual dominance is widely believed to be a product of fire; however, evidence for this is largely anecdotal. We used two long-term data sets, the Monitoring and Burn Severity and the Rangeland Analysis Platform, to investigate when the transition to annual grass dominance occurred. We found that 80% of the transitions to annual grass dominance occurred in the absence of fire. This suggests that annual grasses are highly competitive in these rangelands and that they can likely facilitate the transition in the absence of major disturbances. These results are of interest to rangeland managers, invasive plant managers, other scientists, and the general public.

Technical Abstract: Sagebrush ecosystems of western North America are experiencing widespread loss and degradation by invasive annual grasses. Positive feedbacks between fire and annual grasses are often invoked to explain the rapid pace of these changes, yet annual grasses also appear capable of achieving dominance among vegetation communities that have not burned for many decades. Using a dynamic, remotely-sensed vegetation dataset in tandem with remotely-sensed fire perimeter and burn severity datasets, we examine the role of fire in transitions to and persistence of annual grass dominance in the U.S. Great Basin over the past 3 decades. Although annual grasses and wildfire are so tightly associated that one is rarely mentioned without the other, our findings reveal surprisingly 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 predominantly reactive management (e.g., aggressive fire suppression and post-fire restoration in heavily-infested areas) to more proactive management (e.g., enhancing resistance and managing propagule pressure in minimally-invaded areas) is urgently needed to halt the loss of Great Basin sagebrush ecosystems.