The study finds that wildfires are not the primary factor in the expansion of annual invasive grasses in the Great Basin

The study finds that wildfires are not the primary factor in the expansion of annual invasive grasses in the Great Basin

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Composition of pixels that transitioned to the grass-dominated annual group. Data are from 2,632 field monitoring plots measured from 2011 to 2020 under the AIM programme. Panel A shows leaf cover estimated using the point-line intersection method using all results (total cover can be >100%). Panel B shows the number of AIM plots with each combination of primary and secondary plant functional type, where primary and secondary indicate the plant functional types with the highest and second highest cover in the plot, respectively. credit: Biological conservation (2023). doi: 10.1016/j.biocon.2023.110299

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Composition of pixels that transitioned to the grass-dominated annual group. Data are from 2,632 field monitoring plots measured from 2011 to 2020 under the AIM programme. Panel A shows leaf cover estimated using the point-line intersection method using all results (total cover can be >100%). Panel B shows the number of AIM plots with each combination of primary and secondary plant functional type, where primary and secondary indicate the plant functional types with the highest and second highest cover in the plot, respectively. credit: Biological conservation (2023). doi: 10.1016/j.biocon.2023.110299

Scientists examined the assumption that wildfires are the primary factor driving the expansion of invasive annual grasses that dominate shrubs and grasslands in the U.S. Great Basin, and found that annual grasses are highly competitive even in the absence of major disturbances such as fire.

In fact, according to the study conducted by scientists at the U.S. Department of Agriculture (USDA) Agricultural Research Service and Wildlife Working Lands for researchers affiliated with the University of Montana (UMT), nearly 80% of the shrubs and grasslands in the Great Basin of the United States that have transitioned to dominance An annual on grass, it has done so without burning in the past ten years.

Native perennial grasses and shrubs play a critical role in arid and semiarid regions of the Great Basin of the United States, where they benefit wildlife, provide forage for livestock, and sequester carbon. The rapid spread of invasive annual weeds, including cheatgrass (Bromus tectorum), meadowgrass (Taeniatherum caput-medusae), red brome (B. rubens), Ventenata dubia, and others, has fundamentally changed these plant communities .

As annual grasses invade, they fill in the spaces between native perennial grasses and shrubs. This creates near-continuous fuel that dries out early in the growing season, allowing wildfires to ignite and spread and creating a grass fire cycle, contributing to the widespread dominance of invasive annual grasses and increasing the chances of wildfires. Previous studies have revealed that these grasses already dominate a fifth of the Great Basin’s grasslands, causing major ecological disturbances.

“We found that wildfires are not the primary driver of invasive annual grass expansion in the Great Basin, but they remain a major issue that can enhance annual grass abundance and negatively impact a wide range of ecosystem services and values ​​ranging from forage to livestock production,” said Chad Boyd, co-author. “Sagebrush is obligatory for wildlife habitats,” said research chief at the USDA Forage and Grassland Management Research Unit.

“However, annual weed management that focuses solely on wildfire suppression and post-fire recovery is unlikely to reverse the widespread shift to invasive annual weeds.”

The research team used dynamic datasets derived from remote sensing from 1994 to 2020 to analyze shifts in annual grass dominance in the Great Basin of the United States.

Datasets included fire perimeter and burn severity datasets obtained from the Burn Severity Trends Monitoring Program and maps of grass-dominated annual vegetation communities based on the Rangeland Analysis Platform.

Data examined over 26 years by scientists in the study show that wildfires are not the main factor driving the rapid expansion, decline, and control of native plant communities by annual grasses in the region. Adopting a preventive approach to managing invasive grasses before wildfires occur is essential to controlling the grass fire cycle and slowing transitions to annual grass dominance.

“Firefighters extinguish 97% of wildfires before they reach 1,000 acres, yet we are still surrounded by overgrown grass,” said Joe Smith, co-author and affiliate member of NRCS-Working Lands for Wildlife at UMT. “We need to get ahead of future fires by proactively defending healthy landscapes against cheatgrass expansion.”

The research is published in the journal Biological conservation.

more information:
Joseph T. Smith et al., fire needs annual grasses more than annual grasses need fire, Biological conservation (2023). doi: 10.1016/j.biocon.2023.110299

Magazine information:
Biological conservation

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