|Mullen Fire affected area near Pelton Creek road. Photo Credit: Tanner Hoffman.
“Recovery of Below- and Above-ground Biodiversity Following the Mullen Wildfire” is an ongoing project at the University of Wyoming focusing on interactions between plants and belowground microorganisms. Microorganisms are organisms that are invisible to the naked eye such as bacteria and fungi. The goal of this project is to gain a better understanding of the post-fire recovery of soil microbial and plant communities, and how cheatgrass and herbicide application affect this process. This work is done in collaboration with the USDA Forest service as they monitor vegetation recovery, and apply the herbicide Indaziflam (Rejuvra) to Mullen fire affected areas that are susceptible to invasion by cheatgrass (Bromus tectorum).
The number of wildfires in the western United States has steadily increased over the last few decades, which has been mainly attributed to land management, fire suppression and changes in climate. Wildfires have historically acted as a key component to maintaining the aboveground biodiversity of arid and semi-arid landscapes. However, increases in invasive plant species are becoming more common post-fire likely due to increases in freeze-free seasons, alterations in winter precipitation patterns, and the lengthening of fire seasons. In Fall 2020, the Mullen Fire burned over 175,000 acres in the Medicine Bow National Forest in Southeastern Wyoming. The Burned Area Emergency Response program (BAER) indicated that over 110,000 acres contain moderate to severe soil burn severity. Burned soils will have drastic changes in above- and belowground biology.
Soil microorganisms form complex relationships with plants, serving as key players in maintaining plant health and functionality in natural ecosystems. In particular, mycorrhizal fungi and plants act in a mutualistic fashion; the fungi acquire nutrients and water for plants, in return for energy resources from the plant. Plant-microbe interactions may be significantly altered by the presence of invasive plants, which are more likely to invade ecosystems after severe disturbances such as wildfire. Cheatgrass , in particular, is thought to be able to outcompete native grasses during an ecosystem’s recovery from wildfire because it does not need mycorrhizal fungi like native grasses do. This is compounded by mycorrhizal fungal abundance and diversity, which can be greatly reduced after a fire. Cheatgrass can have a myriad of negative effects on an ecosystem, including decreases in the abundance and biodiversity of native grasses and small mammals, and increasing the susceptibility of ecosystems to fire.
|Left: Early season (late spring/early summer) cheatgrass. Right: late season (mid to late summer/fall) cheatgrass. Photo: Linda van Diepen
Although chemical herbicides are often prescribed for cheatgrass control, many fail to consistently control it. In addition, herbicides applied to control cheatgrass often have negative impacts on native grasses. In 2016, Indaziflam, a broad spectrum pre-emergence herbicide, was approved for use to aid in the restoration of natural areas, including fire rehabilitation areas. In the summer of 2021, Indaziflam was applied to Mullen Fire affected areas in the Medicine Bow National Forest to combat cheatgrass.
In an ongoing effort to untangle the intricacies of how soil microorganisms respond to wildfire, non-native plant invasion, and herbicide application, we need your help!
Top: Arbuscular mycorrhizal fungi (AMF) is associated with sagebrush and grasses, including cheatgrass. The fungus enters the root cells of the plant and forms tiny arbuscles, or tree-like structures. Bottom: Ectomycorrhizal fungi is associated with coniferous trees. The fungus surrounds the root cells of the plant, but does not penetrate the cells. Photos: top - Linda van Diepen; bottom - Tanner Hoffman.