Jennifer Zavaleta, M.S. 2012
Texas Tech University
Dr. David Haukos
Dr. Clint Boal
Grasslands Charitable Foundation
Texas Tech University
Location: Eastern New Mexico
Completion: March 2012
Study area in eastern New Mexico, showing application of tebuthiuron and grazing treatments
(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.
Zavaleta, J. 2012 Effects of grazing and herbicide treatments to restore degraded
sand shinnery oak grasslands. Thesis, Texas Tech University.