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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #307928

Research Project: Assessment, Conservation and Management of Rangelands in Transition

Location: Northwest Watershed Research Center

Title: Hydrologic impacts of woodland encroachment and tree removal in Great Basin sagebrush steppe

Author
item Williams, Christopher - Jason
item Pierson, Fred
item AL-HAMDAN, OSAMA - University Of Idaho

Submitted to: Society for Ecological Restoration Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/25/2014
Publication Date: 10/6/2015
Publication URL: http://handle.nal.usda.gov/10113/1300256
Citation: Williams, C.J., F.B. Pierson, and O.Z. Al-Hamdan. 2014. Hydrologic Impacts of Woodland Encroachment and Tree Removal in Great Basin Sagebrush Steppe. Presented at the 2014 Joint Regional Conference of the Society for Ecological Restoration, Northwest and Great Basin Chapters, Collaborative Restoration: From Community Efforts to Landscape Scales, October 6-10, 2014, Redmond, Oregon.

Interpretive Summary:

Technical Abstract: Extensive woodland expansion in the Great Basin has generated concern regarding the ecological impacts of tree encroachment on sagebrush (Artemisia spp.) rangelands. This study used rainfall and concentrated flow experiments and measures of vegetation, ground cover, and soils at three sites to investigate hydrologic and erosion impacts of woodland encroachment and tree-removal restoration treatments on sagebrush-steppe. Prior to tree removal, each site exhibited a degraded intercanopy with high rates of runoff and erosion. Areas underneath tree canopies (tree zones) generated low runoff and erosion rates, but occupied only 25% of the area at each site. Falling trees into the intercanopy did not affect vegetation, ground cover, runoff, or erosion over one growing season. However, placement of mulched tree debris into interspaces between shrubs and trees enhanced infiltration and reduced erosion following whole-tree mastication. Fire removal of litter and herbaceous cover increased tree zone runoff and erosion at two sites, but had minimal impact at the other site. Site differences were attributed to burn severities and site-specific erodibilities. Burning increased erodibility within the intercanopy, but did not affect intercanopy cumulative runoff from the high-intensity rainfall simulations. One year following fire, erosion from overland flow experiments was greater on burned than unburned tree zones, and erosion for burned tree zones was significantly greater for the sites with higher burn severity. Fire-induced increases in erosion persisted for tree zones at all sites two years post-fire. In contrast, enhanced herbaceous cover on burned intercanopy plots two years post-fire reduced fire impacts on intercanopy erodibility at each site. The net impact of burning included an initial increase in erosion risk, particularly for tree zones, followed by improved hydrologic function within the intercanopy two growing seasons post-fire. The overall results indicate that erosion from late-succession woodlands is reduced primarily through herbaceous and ground cover recruitment with the intercanopy.