PS 45-197 - Is extreme fire the key to reversing grassland loss due to woody encroachment? A test in the tallgrass prairie.

Abstract: Over the last century, the invasion of woody plants has threatened grassland conservation worldwide. Woody encroachment in grasslands tends to decrease plant biodiversity, surface water availability, and limit cattle production. The expansion of woody encroachment is linked to changes in land management, especially the suppression of fire and removal of native herbivores. In the past, frequent low-intensity prescribed fires were enough to control the expansion of woody encroachment. However, prescribed fire alone is no longer able to control woody encroachment in areas where fire has been absent for three or more years. In this study, we evaluate if extreme fire (a high-intensity fire that exhibits unique behaviors) could be used to control woody encroachment. This study takes place at the Konza Prairie Biological Station in the Central Great Plains (U.S.A.). We took advantage of an accidental wildfire that occurred in April 2021 which burned under very dry and windy conditions, that are usually avoided when conducting a prescribed burn. In 2020 and 2022 we measured the diameters of woody vegetation in two watersheds that burned under two fire treatments: one that burned in the wildfire in 2021 (extreme) and one that underwent typical prescribed fire conditions (prescribed) in the same year. Before the wildfire in 2021, both watersheds burned on a four-year interval. Our results indicated that there was a significant increase in average shrub height between 2020 and 2022 in the prescribed watershed (p = 0.041), while there was no significant increase in height in the extreme watershed (p = 0.64). Stem densities increased significantly in the extreme fire watershed (p = 0.021), which reflects that many adult stems were killed, leading to coping strategies in the woody communities. The decrease in average height and increase in new stems could leave woody plants in the extreme watershed to be more susceptible to prescribed fire events in the future. This study will continue through the summer of 2024 when the watersheds will undergo the first prescribed fire after the wildfire. Finding new ways to manage woody encroachment will be crucial to conserve and protect grasslands in the future.