Soil and hydrologic response to mastication of juniper woodlands

Nathan Cline, M.S. Candidate, Brigham Young University

Bruce Roundy

Fred Pierson

This study is looking at the impacts of juniper mastication (using a Bull Hog) on soil compaction and hydrologic response at the SageSTEP Onaqui site in Utah. This study measured differences in soil water infiltration rates between soils tracked by the Bull Hog tractor and those not tracked, as well as infiltration rates of soils covered and not covered with mastication residue.

The study site has a gravelly loam soil texture. Plots of two different sizes or scales were measured; microsites (0.5 m2 plots), and canopy/intercanopy sites (13 m2 plots). Rain simulations were applied at two different rates as part of a larger SageSTEP hydrology study. Pre-treatment data were collected in the summer of 2006. Bull Hog mastication of juniper trees took place in fall 2006. First-year post-treatment data were collected in summer 2007.

Study results show that plant microsites had higher infiltration rates than bare ground microsites between the plant microsites. Soils tracked by the Bull Hog had similar infiltration rates as untracked soils on this hill slope. Soils covered with residue had higher infiltration rates than bare soils. Compaction, as measured by penetration resistance, was greater on tracked than untracked soils for all microsites except tree microsites. Although Bull Hog tracking did compact soils, infiltration rates of both tracked and untracked soils were high in this study. Because compaction could reduce infiltration rates on other soils and sites with greater slopes and finer soil textures, land managers should monitor post-mastication responses and avoid mastication when soils have high soil water content.

Tracked bare ground microsite.	Mulch piles left behind by tree mastication.