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ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #310178
Title: Mechanical mastication of Utah juniper encroaching sagebrush steppe increases inorganic soil N

Author
item YOUNG, KERT - New Mexico State University
item ROUNDY, BRUCE - Brigham Young University
item EGGETT, DENNIS - Brigham Young University

Submitted to: Applied and Environmental Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2014
Publication Date: 4/27/2014
Citation: Young, K.R., Roundy, B.A., Eggett, D.L. 2014. Mechanical mastication of Utah juniper encroaching sagebrush steppe increases inorganic soil N. Applied and Environmental Soil Science. 2014, Article ID 632757.

Interpretive Summary: Juniper trees have encroached millions of hectares of sagebrush steppe. Juniper mechanical mastication (tractors shredding standing trees) increases cover of understory species, but could increase resource availability and subsequently invasive plant species that are adapted to grow quickly when resources are available. We measured the effects of juniper mastication on soil nutrient availability in the Utah portion of the Great Basin. Mastication increased inorganic N across the treatment area and seasons by ending juniper tree uptake of soil resources but the high C and low N in the woody masticated-tree material resulted in less inorganic N than uncovered areas during late-summer through winter. Mastication does not appear to alter soil nutrient availability sufficiently to favor dominance of invasive annual grasses over perennial grasses. We expect both plant life forms to increase in cover following juniper mastication. These results suggest that the plant species growing on a site prior to mastication are likely to continue growing on the site after mastication.

Technical Abstract: Juniper (Juniperus spp.) has encroached millions of hectares of sagebrush (Artemisia spp.) steppe. Juniper mechanical mastication increases cover of understory species, but could increase resource availability and subsequently invasive plant species. We quantified the effects of juniper mastication on soil resource availability by comparing total C, total N, C:N ratio, Olsen extractable P, sulfate S, and pH using soil samples and inorganic N (NO3- + NH4+) using ion exchange membranes. We compared resource availability in paired masticated and untreated areas in three juniper-dominated sagebrush and bunchgrass ecosystems in the Utah portion of the Great Basin. Inorganic N was 4.7 times higher in masticated than untreated areas across seasons (P<0.001). Within masticated areas, tree mounds of juniper leaf scales and twigs served as resource islands with 1.9 times higher inorganic N and total C, and 2.8 times higher total N than bare interspaces across seasons (P<0.01). Bare interspaces had 3.0-3.4 times higher inorganic N than interspaces covered with masticated trees during late-summer through winter (P<0.01). Soil fertility changes associated with mastication were not considered sufficient to favor establishment of annual over perennial grasses, and we expect both to increase in cover following juniper mastication.