Pyrogeography of the Western Great Plains: A 40-year history of fire in semi-arid rangelands

Authors: McGranahan, Devan; Wonkka, Carissa

Submitted to: Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2024
Publication Date: 1/17/2024
Citation: McGranahan, D.A., Wonkka, C.L. 2024. Pyrogeography of the Western Great Plains: A 40-year history of fire in semi-arid rangelands. Fire. 7(1). Article 32. https://doi.org/10.3390/fire7010032.
DOI: https://doi.org/10.3390/fire7010032

Interpretive Summary: Using publicly-available wildfire records from 1992-2020, we show that ignition by humans was the dominant cause of wildfires in the four ecoregions of the Western Great Plains. The Northwestern Plains had the most burned area and the greatest number of incidents -- consistently around or above 1000 incidents per year since 1992 -- with the majority in July. The High Plains showed the greatest increase in annual fire frequency, never reaching more than 200-300 per year 1992-2009, and averaging above 1000 incidents per year since 2010. Rural Western Great Plains landscapes are a mosaic of public and private land ownership, and an increasing impact of wildfire on public grazinglands -- which are often situated within other jurisdictions or ownership -- will likely have an impact on rural livelihoods.

Technical Abstract: This study describes spatial and temporal patterns in fire across the US Western Great Plains over the last 40 years. Although pyrogeographic studies have explored the nexus of fire patterns in relation to the bio-physical environment and socio-ecological trends, most of this research has focused on forested ecosystems and regions long known for conflict between wildfire and human development, especially at the wildland-urban interface. But evidence suggests large wildfire activity is increasing in the US Great Plains, and the Western Great Plains -- a Land Resource Region comprised of four ecoregions, Northwestern Plains, High Plains, Nebraska Sandhills, and Southwestern Tablelands -- not only contains some of the largest areas of rangeland in the US, but also the highest concentration of public land in the Great Plains. As such, the Western Great Plains provides an opportunity to explore fire activity in primarily rural landscapes with a combination of public and private ownership, all dominated by rangeland vegetation. We combined several publicly-available datasets containing fire records between 1992-2020 to create two databases, one with georeferenced point data on 60,575 wildfire events in the region, and another with georeferenced perimeter data for 2,665 fires. Ignition by humans was the dominant cause of fires. The Northwestern Plains had the most burned area and the greatest number of incidents -- consistently around or above 1000 incidents per year since 1992 -- with the majority in July. The High Plains showed the greatest increase in annual fire frequency, never reaching more than 200-300 per year 1992-2009, and averaging above 1000 incidents per year since 2010. Few long-term trends in human population, weather, or fuel metrics appear strongly associated with fire patterns in any ecoregion, although the years 2006, 2012, and 2017 stood out for their levels of fire activity, and these years often frequently logged extreme values in wildland fuel metrics. These relationships merit much closer examination in the Western Great Plains, because like other rangeland-dominated landscapes, the fine fuels that comprise these wildland fuelbeds are much more responsive to fine-scale changes in moisture conditions. Rural Western Great Plains landscapes are a mosaic of public and private land ownership, and an increasing impact of wildfire on public grazinglands -- which are often situated within other jurisdictions or ownership -- will likely have an impact on rural livelihoods.