NOAA/WDS Paleoclimatology - Heyerdahl fire data from Weitz, Palouse northwestern United States - IMPD USWEI001

Prairie-forest ecotones are ecologically important for biodiversity and ecological processes. While these ecotones cover small areas, their sharp gradients in land cover promote rich ecological interaction and high conservation value. Our objective was to understand how historical and current fire occurrences and human development influenced the Palouse Prairie-forest ecotone. We used General Land Office survey field notes about the occurrence of bearing trees to locate historical (1870s to 1880s) prairie, pine savanna, and forest at the eastern edge of the bioregion. We combined LANDFIRE Existing Vegetation classes to contrast historical land cover with current land cover. We reconstructed historical fire occurrence (1650 to 1900) from fire-scarred trees. We used fire and lightning records from 1992 to 2015 to interpret the role of people and lightning. Historically, the ecotone was a matrix of prairie with some pine savanna and forest (72%, 16%, and 12% of GLO points, respectively). The prairie and pine savanna have been largely converted to agriculture, perennial vegetation under the Conservation Reserve Program, or residential development while the forest has not been converted. Fires were historically frequent, occurring on average every 5 to 8 years at most sites. Lightning was not frequent but could likely have been sufficient to ignite fires that could spread readily given the rolling terrain and long fire season. Fire was far more frequent historically than currently. Lightning and people may ignite fires that spread readily in the future as conservation, restoration, and other land-use changes result in more continuous vegetation and hence fuel for fires. Understanding the past and potential future of fire in the Palouse Prairie bioregion may help us live with fire while conserving ecological values here and in similar prairie-forest ecotones.