Fire, plant invasions, and erosion events on western rangelands

Authors: Pierson Jr, Frederick; Williams, Christopher - Jason; Hardegree, Stuart; Weltz, Mark; Stone, Jeffry; Clark, Pat

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2011
Publication Date: 9/13/2011
Citation: Pierson Jr, F.B., Williams, C.J., Hardegree, S.P., Weltz, M.A., Stone, J.J., Clark, P. 2011. Fire, plant invasions, and erosion events on western rangelands. Rangeland Ecology and Management. 64(5):439-449. DOI: 10.2111/REM-D-09-00147.1.

Interpretive Summary: Landscape plant community transitions across western United States rangelands have altered fire regimes and present large-scale environmental consequences relative to rangeland hydrology. Extensive conversion of shrublands to annual grasslands has increased the spatial extent and frequency of fires in wildland settings and along the urban-wildland interface. The shift in fire regimes to larger-scale, more frequent and severe burning amplifies the spatial and temporal exposure and vulnerability of these rangeland landscapes to greater runoff and erosion and poses significant risks to habitat, water quality, property, and human life. This paper explores the potential hydrologic impacts of large-scale plant community transitions and altered fire regimes and proposes a conceptual framework for assessing post-fire hydrologic risk and recovery. Fire effects on rangeland hydrologic vulnerability are presented through a review of published field studies from semi-arid rangeland and forested sites. The manuscript provides an extensive review of fire effects on rangeland hydrology and highlights the need for additional research in lieu of the of ongoing altered fire regimes on western rangeland landscapes.

Technical Abstract: Millions of hectares of rangeland in the western United States have been invaded by annual and woody plants that have increased the role of wildland fire. Altered fire regimes pose significant implications for runoff and erosion. In this paper we synthesize what is known about fire impacts on rangeland hydrology and erosion, and how that knowledge advances understanding of hydrologic risks associated with landscape scale plant community transitions and altered fire regimes. The increased role of wildland fire on western rangeland exposes landscapes to amplified runoff and erosion over short- and long-term windows of time and increases the risk of damage to soil and water resources, property, and human lives during extreme events. Amplified runoff and erosion post-fire are a function of fire-induced changes in site characteristics (i.e. ground cover, soil water repellency, aggregate stability, surface roughness) that define site susceptibility. We suggest that overall post-fire hydrologic vulnerability be considered in a probabilistic framework that predicts hydrologic response for a range of potential storms and site susceptibilities and that identifies the hydrologic response magnitudes at which damage to values-at-risk are likely to occur. We identify key knowledge gaps that limit advancement of predictive technologies to address the increased role of wildland fire across rangeland landscapes. Our review of literature suggests quantifying interactions of varying rainfall intensity and key measures of site susceptibility, temporal variability in strength/influence of soil water repellency, and spatial scaling of post-fire runoff and erosion remain paramount areas for future research to address hydrologic effects associated with the increased role of wildland fire on western rangelands.