The infuence of wildfire on invasive plant abundance and spatial structure in eastern ponderosa pine savanna

Authors: DONOVAN, VICTORIA - University Of Nebraska; Wonkka, Carissa; ROBERTS, CALEB - University Of Nebraska; WEDIN, DAVID - University Of Nebraska; McGranahan, Devan; TWIDWELL, DIRAC - University Of Nebraska

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2023
Publication Date: 9/25/2023
Citation: Donovan, V.M., Wonkka, C.L., Roberts, C.P., Wedin, D.A., Mcgranahan, D.A., Twidwell, D. 2023. The infuence of wildfire on invasive plant abundance and spatial structure in eastern ponderosa pine savanna. Plant Ecology. Online. https://doi.org/10.1007/s11258-023-01355-9.
DOI: https://doi.org/10.1007/s11258-023-01355-9

Interpretive Summary: Non-native plant invasion has been linked to fire across much of the western U.S.; however, relationships between fire and invasive species can vary. In eastern ponderosa pine savannas, it is unclear how an increasing number of wildfires have influenced plant invasions. We sampled invasive plant species across a three wildfires that occurred different numbers of years ago to determine (1) the status of plant invasion, (2) if invasive plant species are more common in burned areas, and if (3) time since fire and (4) fire severity influence invasive species occurrence and cover. We found complex relationships between wildfires and invasive species in eastern ponderosa pine savanna that differed from typical generalizations made between invasive plants and fire. Cheatgrass was by far the most dominant invasive species sampled, followed by Kentucky bluegrass and smooth brome. Cheatgrass and Kentucky bluegrass were more common in burned areas. Kentucky bluegrass cover was found to decrease with time since fire. Cheatgrass occurrence was higher in low and moderate severity burned areas than in unburned locations. While cheatgrass occurred at a similar number of sample sites in unburned and high severity burned areas, cheatgrass cover was lower at high severity burned sites compared to unburned sites. Our results show variability in wildfire-invasive plant dynamics in eastern ponderosa pine savannas and the importance of making environment-specific decisions tied to invasive species management in response to wildfire.

Technical Abstract: Fire can alter the trajectory for plant invasions; however, invasive plant responses to fre vary among regions and species. It is unclear how recent increases in large, mixed-severity wildfres in eastern ponderosa pine forests of North America have infuenced patterns in plant species invasion. We sampled invasive plant species across three mixed-severity wildfre perimeters over 3666 sample sites in eastern ponderosa pine of western Nebraska, USA. Our analysis sought to determine whether invasive species occurred more frequently and at greater abundance in burned areas, and whether either frequency of occurrence or abundance of invasive plants could be explained by fre severity. We found complex relationships between mixed-severity wildfre and invasive plant species. Cheatgrass (Bromus tectorum) was the most common invasive species sampled, followed by Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis). Cheatgrass and Kentucky bluegrass were more common in burned areas. Cheatgrass occurrence was higher in low and moderate severity burned areas than in unburned locations. While cheatgrass occurred at a similar number of sample sites in unburned and high severity burned areas, cheatgrass cover was lower at high severity burned sites compared to unburned sites. Our results emphasize variation in invasive plant species occurrence and cover in relation to fre in eastern ponderosa pine savannas and the importance of making ecosystem specifc decisions regarding invasive species management in response to wildfre