Investigators:
Jennifer Zavaleta, M.S. 2012
Texas Tech University

Project Supervisors:
Dr. David Haukos
Dr. Clint Boal

Funding:
Grasslands Charitable Foundation
Weaver Ranch
Texas Tech University

Cooperators:
Charles Dixon
Willard Heck
Jim Weaver

Location: Eastern New Mexico

Completion: March 2012

Status: Completed

Objectives:
(1) Determine the community response to tebuthiuron and grazing treatments used to restore sand shinnery oak grasslands.
(2) Assess the temporal response of the community to the treatment combinations over a 12-year period.
(3) Compare resulting vegetation composition to historical standards.

Results: The sand shinnery oak (Quercus havardii) mixed-grass community is an isolated, relict habitat located within short-grass prairie of the Southern High Plains. With the introduction of center-pivot agriculture, unmanaged grazing, oil and gas exploration and suppression of the natural fire regime, the vegetation composition of the shinnery oak community has changed during the past century. Land managers have used herbicides (e.g., tebuthiuron) and a variety of grazing systems as tools to manage shinnery oak. Results show that at relatively low levels of tebuthiuron (0.60 kg/ha) and subsequent moderate grazing system, sand shinnery oak can be reduced and maintained at near historical levels without reapplying tebuthiuron because the tested management approach allowed grasses to remain competitive in the system. There was 91% less shinnery oak in untreated areas. The removal of shinnery oak made environmental soil moisture more available for grasses and forbs to germinate and grow. Grasses increased by 149% and forbs increased by 257% in treated areas as compared to untreated areas throughout the study period. In terms of visual obstruction, there was both an herbicide and grazing effect in April such that visual obstruction increased by 30% in treated areas as compared to untreated and decreased by 6.5% in grazed areas as compared to non-grazed areas. There was no significant herbicide effect of overall abundance of small mammals. However, there was a significant grazing effect such that there was 23% more abundance of small mammals in grazed areas as compared to non-grazed areas, which was likely driven by kangaroo rats. Areas that were treated with tebuthiuron and had moderate grazing statistically reached historical standards only during one year, but showed trends that were comparable to historical standards throughout the study compared to other treatment combinations. The largest difference between treated areas and historical standards was that treated areas had more forbs. The change from a shrub monoculture to a mixed-grass prairie changes the plant composition and structure and provides more niches for invertebrates, mammals and herptiles to fill.

Products:
Zavaleta, J. 2012 Effects of grazing and herbicide treatments to restore degraded sand shinnery oak grasslands. Thesis, Texas Tech University.