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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #228009
Title: Hydrologic and erosional impacts of pinyon and juniper encroachment into sagebrush steppe communities of the Great Basin, USA.

Author
item Pierson Jr, Frederick
item Kormos, Patrick
item Williams, Christopher - Jason

Submitted to: International Soil and Water Conservation Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2008
Publication Date: 5/18/2008
Citation: Pierson Jr, F.B., Kormos, P.R., and Williams, C.J. 2008. Hydrologic and erosional impacts of pinyon and juniper encroachment into sagebrush steppe communities of the Great Basin, USA. In: Proceedings of the 15th International Congress of the International Soil and Water Conservation Organization, May 18-23, 2008, Budapest-Hungary. CD-ROM.

Interpretive Summary: Historical research of pinyon and juniper woodland expansion in the western United States suggests woodland encroachment into sagebrush steppe may reduce shrub and herbaceous cover and increase the expanse of interspace areas (areas between shrub and tree canopies). Studies from woodland sites in southwestern United States indicate surface runoff and erosion rates are highest from interspace areas and lowest near bases of shrubs and trees protected by canopy and litter. Rainfall simulation over small (0.5 m2) and large (13 m2) plot scales and concentrated flow experiments were applied across a ground cover gradient to determine whether critical thresholds exist in ground cover that significantly influence infiltration, runoff, and erosion in pinyon and juniper woodlands. Preliminary results indicate runoff and erosion from pinyon and juniper woodlands are greater from shrub-interspace (shrub areas with varying amounts of interspace) than tree (tree areas with minor amounts of interspace) patches and that the impacts of woodland encroachment on runoff and erosion likely depend on the influence it has on interspace extent and connectivity. The results provide land management agencies and private land owners a measure of the relative contributions of shrub, tree, and interspace areas to runoff and erosion in pinyon and juniper woodlands, provide insight into the potential hydrologic impacts of woodland encroachment into sagebrush steppe ecosystems in the Great Basin, USA, and establish a baseline data set for future evaluation of the hydrologic effects of woodland control treatments.

Technical Abstract: ersion of sagebrush steppe to pinyon and juniper woodlands has been linked to changes in plant community structure and composition, reduced forage production, altered wildlife habitat, and increased runoff and erosion. The Sagebrush Steppe Treatment Evaluation Project (SageSTEP, www.sagestep.org) was implemented in 2005 as a 5 year interdisciplinary research study to evaluate restoration methodologies for sagebrush rangelands degraded by woodland and annual grassland encroachment over a six state area of the Great Basin, USA. The hydrology component of SageSTEP focuses on the relationships between changes in vegetation and ground cover and runoff/erosion processes. Rainfall simulation over small (0.5 m2) and large (13 m2) plot scales and concentrated flow experiments were applied across a ground cover gradient to determine whether critical thresholds exist in ground cover that significantly influence infiltration, runoff, and erosion in pinyon and juniper woodlands. Water drop penetration times were used to investigate the influence of soil water repellency on infiltration. Preliminary results indicate runoff and erosion from pinyon and juniper woodlands are greater from interspace than vegetated areas and that impacts of woodland encroachment on runoff and erosion likely depend on the influence it has on interspace extent and connectivity. Furthermore, static (soil properties, hillslope angle) and variable (soil water repellency) site characteristics may mitigate or enhance hydrologic impacts of woodland encroachment.