Fire and land cover change in the Palouse Prairie\u2013forest ecotone, Washington and Idaho, USA

Penelope Morgan,Max Nielsen-Pincus,John T Abatzoglou,James P Riser Ii,Stephen C Bunting,Eva K Strand,Emily K Heyerdahl,Mara Johnson

doi:10.1186/s42408-019-0061-9

Abstract

BackgroundPrairie–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.ResultsHistorically, the ecotone was a matrix of prairie with extensive savanna and some forest. More than half of the ecotone area was prairie, which is now dominated by agriculture, with some residential development. The 16% of the landscape that was pine savanna is now forest or shrubs, agriculture, perennial vegetation under the Conservation Reserve Program, or developed; no savanna now exists. Forests covered 12% of the ecotone and these are still mostly forest. 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.ConclusionsFire was far more frequent historically than currently. Conservation, restoration, and other ongoing land-use changes will likely result in more continuous vegetation and hence fuel for fires. Lightning and people may ignite fires that therefore spread readily in the future. 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.

Highlights

Prairie–forest ecotones are ecologically important for biodiversity and ecological processes
lightning-ignition efficiency (LIE) exhibits seasonal and interannual variability due to variations in fuel moisture and abundance; we considered a single LIE for each 4-km grid cell by tabulating the total number of lightning strikes and lightning-caused fires ignited within each grid cell for May to September, 1992 to 2015
Residential development has led to conversion from agricultural fields to other land cover (Pocewicz et al 2008) with conservation implications (Goldberg et al 2011)

Summary

Introduction

Prairie–forest ecotones are ecologically important for biodiversity and ecological processes. Prairie–forest ecotones have been greatly altered by human activity (Samson and Knopf 1994; Bowman et al 2011; Harvey et al 2017). Both prairies and adjacent forests have been reduced in extent and health through agriculture, livestock grazing, fire exclusion, and residential development (Samson and Knopf 1994; Pocewicz et al 2008), which has likely affected primary productivity, hydrology, and many ecosystem services. Fires were and are ecologically important in prairies on every continent (Bowman et al 2009) as they reduce tree encroachment and foster biodiversity Lawson) forests were more frequent near prairies than far from them (Brown and Sieg 1999). Conver et al (2018) suggested that prairie–forest ecotones may have been corridors for fire to spread into forests

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