Location: Northwest Watershed Management Research
Title: Hydrologic response of sagebrush steppe to woodland encroachment and subsequent tree removal: implications for assessing sagebrush steppe hydrologic stability and resiliency Authors
Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 25, 2011
Publication Date: January 29, 2012
Citation: Pierson, F.B., Williams, C.J., Kormos, P.R., and Al-Hamdan, O.Z. 2012. Hydrologic Response of Sagebrush Steppe to Woodland Encroachment and Subsequent Tree Removal: Implications for Assessing Sagebrush Steppe Hydrologic Stability and Resiliency. In: Abstracts of the 65th Annual Meeting of the Society for Range Management, January 29 - February 3, 2012, Spokane, WA. Technical Abstract: Woodland encroachment into sagebrush-steppe potentially amplifies runoff and erosion by altering site characteristics that dictate site hydrologic state. The amount and distribution of ground cover, soil erodibility, and climate (site productivity) dictate inherent resilience of a site relative to soil and water retention. Resource conserving sagebrush-steppe typically maintains 40-50% ground cover, has low erodibility, and resists soil loss by water. Tree encroachment into sagebrush-steppe promotes water and soil loss by increasing bare ground connectivity, and amplifying runoff generation. Initial tree encroachment (Phase I) minimally impacts runoff and erosion, but continued encroachment (to Phase II-III) may cause a shift from a resource-conserving to a non-conserving state. Sites on soils with inherently low infiltration and high erodibility may rapidly transform to a non-conserving state (particularly under drought conditions) as tree dominance (Phase III) promotes bare interspace (area between trees) expanse/connectivity. Tree removal is most often aimed at improving shrub and herbaceous cover and structure, which increases infiltration and aggregate stability. This study evaluated: 1) the hydrologic effects of tree encroachment into sagebrush rangelands, 2) the short-term (0-2 years) effects of tree removal on hydrologic stability, and 3) variations in hydrologic resilience following tree removal across three woodland invaded sagebrush rangelands in the Great Basin, USA. Our results demonstrate the importance of considering ecological sites and inherent hydrologic properties (i.e., infiltration, soil erodibility) when choosing tree removal strategies and reveal potential hydrologic benefits of Phase I-II tree removal versus consequences of Phase III tree removal or long-term conversion of sagebrush-steppe to woodland dominance.