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United States Department of Agriculture

Agricultural Research Service

Research Project: DISTURBANCE ASSESSMENT AND MITIGATION OF GREAT BASIN RANGELAND Title: Hydrologic response of mechanical mastication in juniper woodland in Utah

Authors
item Cline, Nathan -
item Roundy, Bruce -
item Pierson, Frederick
item Kormos, Patrick
item Williams, Christopher

Submitted to: Society for Range Management Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: September 4, 2008
Publication Date: February 8, 2009
Citation: Cline, N.L., Roundy, B.A., Pierson Jr, F.B., Kormos, P.R., Williams, C.J. 2009. Hydrologic Response of Mechanical Mastication in Juniper Woodland in Utah. In: Proceedings of the 62nd Annual Meeting, Merging Trails: Culture, Science, and Innovation, Society for Range Management, February 8-12, 2009, Albuquerque, NM.

Interpretive Summary: Various vegetation control methods have been used to reduce juniper (Juniperus ssp.) woodland encroachment. Mechanical mastication (reducing trees to a mulch residue) has recently been used in some western states. We investigated the hydrologic impacts of rubber tire tracks from the masticating vehicle and mulch residue from juniper mastication on site with a 15% slope and gravelly loam soil on the Onaqui Mountains of Utah. Two successive rain simulations (64mm and 102mm per hour) were applied on 50 0.5 m2 plots (20 control, 20 tire tracked, and 10 mulch covered). Runoff, sediment yield, ground cover, and soil resistance to penetration were measured. Tracked interspace and tracked shrub microsites were more resistant to soil penetration than non-tracked microsites. Infiltration rates of grass interspaces (>5% grass on a plot) were significantly decreased on tracked plots while no significant change in infiltration rates were found on juniper mounds or on bare interspace plots. Tracking on shrub mounds had no effect on infiltration rates, but tracking significantly decreased the time to the start of runoff for tracked shrub mounds. Mulch residue significantly increased infiltration rates and decreased sediment yields on bare interspace plots. A non-linear regression between the average depth of mulch residue across plots and cumulative sediment produced during the simulation indicates that, on average, a layer as thin as 5 mm provides minimum sediment yields. We conclude that mechanical mastication should have minimal negative hydrologic impacts on similar soils and sites.

Technical Abstract: Various vegetation control methods have been used to reduce juniper (Juniperus ssp.) woodland encroachment. Mechanical mastication (reducing trees to a mulch residue) has recently been used in some western states. We investigated the hydrologic impacts of rubber tire tracks from the masticating vehicle and mulch residue from juniper mastication on site with a 15% slope and gravelly loam soil on the Onaqui Mountains of Utah. Two successive rain simulations (64mm and 102mm per hour) were applied on 50 0.5 m2 plots (20 control, 20 tire tracked, and 10 mulch covered). Runoff, sediment yield, ground cover, and soil resistance to penetration were measured. Tracked interspace and tracked shrub microsites were more resistant to soil penetration than non-tracked microsites. Infiltration rates of grass interspaces (>5% grass on a plot) were significantly decreased on tracked plots while no significant change in infiltration rates were found on juniper mounds or on bare interspace plots. Tracking on shrub mounds had no effect on infiltration rates, but tracking significantly decreased the time to the start of runoff for tracked shrub mounds. Mulch residue significantly increased infiltration rates and decreased sediment yields on bare interspace plots. A non-linear regression between the average depth of mulch residue across plots and cumulative sediment produced during the simulation indicates that, on average, a layer as thin as 5 mm provides minimum sediment yields. We conclude that mechanical mastication should have minimal negative hydrologic impacts on similar soils and sites.

Last Modified: 12/21/2014
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