|Williams, Christopher - Jason|
|KORMOS, PATRICK - Us Forest Service (FS)|
|AL-HAMDAN, OSAMA - University Of Idaho|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2015
Publication Date: 9/6/2015
Citation: Pierson Jr, F.B., Williams, C.J., Kormos, P.R., Al-Hamdan, O.Z., Hardegree, S.P., Clark, P. 2015. Short-term impacts of tree removal on runoff and erosion from sagebrush-steppe hillslopes. Rangeland Ecology and Management. 68:408-422.
Interpretive Summary: Pinyon and juniper (woodland) encroachment have altered the ecological structure and function of millions of hectares of Great Basin shrub-steppe rangelands. Encroachment by these species often reduces understory vegetation, increases bare ground, and amplifies runoff and erosion. Land owners and management agencies across the Great Basin are actively seeking guidelines to restore woodland-encroached rangelands through tree-removal treatments that promote understory vegetation. This study used rainfall simulations and measures of vegetation, ground cover, and soils to investigate short-term (2 yr post-treatment) woodland hydrologic and erosion responses to burning and mechanical tree removal at two woodland-encroached sites. Placing cut-downed trees into the intercanopy between trees had minimal immediate impact on infiltration and soil loss. Prescribed burning increased erosion at both study sites, but the amplified post-fire response was substantially greater at one site than the other due to site-specific soil properties. Fire-induced increases in erosion declined the second year after the fires due to intercanopy herbaceous plant recruitment. The overall results clearly indicate that restoration treatments aimed at reducing soil erosion from woodland-encroached rangelands should focus on intercanopy vegetation and ground cover recruitment, and that the effect of site-specific soil erodibility on erosion during the immediately post-treatment period should be considered when selecting treatment alternatives.
Technical Abstract: Tree-removal is often applied to woodland-encroached rangelands to restore vegetation and improve hydrologic function, but knowledge is limited regarding effects of tree removal on hydrologic response. This study used artificial rainfall and overland flow experiments (9-13 m2) and measures of vegetation and ground cover to investigate short-term (1-2 yr) responses to tree removal at two woodland-encroached sites. Plots were located under trees (tree zone) and in the intercanopy (shrub-interspace zone, 75% of area). Prior to tree removal, vegetation and ground cover were degraded and intercanopy runoff and erosion rates were high. Cutting and placing trees into the intercanopy did not significantly affect vegetation, ground cover, runoff or erosion one year post-treatment. Short-term effects of tree mastication on runoff and erosion were inconclusive. Fire removal of litter and herbaceous cover increased tree-zone runoff and erosion under high-intensity rainfall by four- and 30-fold at one site, but had minimal impact at the other site. Site response differences were attributed to variability in burn conditions and site-specific erodibility. Burning had minimal impact on shrub-interspace runoff and erosion from high-intensity rainfall. One year post-fire, erosion from overland flow experiments was two- to 13-fold greater on burned than unburned tree-zone and shrub-interspace plots, but erosion for burned tree zones was three-fold greater for the more erodible site. Two years post-fire, overland flow erosion remained higher for burned versus unburned tree zones, but enhanced intercanopy herbaceous cover reduced erosion from shrub-interspace zones. The net impact of burning included an initial increase in erosion risk, particularly for tree zones, followed by enhanced herbaceous cover and improved hydrologic function within the intercanopy. The overall results clearly indicate that erosion from late-succession woodlands is reduced primarily through recruitment of intercanopy herbaceous and ground cover.