Summary
Much desert grassland in southeastern Arizona (southwest USA) has been subject to livestock grazing for over a century. National Audubon’s Appleton-Whittell Research Ranch Sanctuary (3,160 ha of desert grassland and oak Quercus woodland) had livestock removed in 1968. Prior to1968 it was moderately cattle-grazed yearlong. Adjacent (and similar) areas support continuous moderate livestock grazing thus providing an opportunity for study of vegetation response to livestock removal. Both areas are grazed by white-tailed deer Odocoileus virginianus and pronghorn antelope Antilocapra americana.
In 1969 in a 400 ha area of the Sanctuary (Bald Hill), 25 (10 x 10 m) permanent plots (approximately 400 m apart, marked with steel posts) were surveyed. Within each, canopy cover of vascular plant species was estimated in 10 randomly located (40 x 40 cm) quadrats. The plots were resurveyed in 1984.
In 1984, a second study location (Sanctuary Border) was selected to allow comparison with an adjacent continuously grazed area (Manila Allotment). The Allotment has been grazed yearlong with 120-140 head of cattle since 1910 (comparable to this Sanctuary locality prior to livestock removal). Six plots were established at 120 m intervals along the Sanctuary border fence. Two 20 m transects were located on each side of (and parallel to) the fence at each plot (30-35 m from the fence to reduce possible fenceline effects, e.g. cattle concentrations). In each transect, canopy cover was estimated in 20 (20 x 50 cm) quadrats. Species were grouped into midgrass, shortgrass, forbs, and shrubs.
Vegetation changes on Bald Hill 16 years after livestock removal included increases in total vegetation cover (29% in 1969 vs. 85% in 1984) and species richness (diversity). In 1969, 22 species were recorded in quadrats, compared to 49 in an equivalent sample size in 1984.
In the Sanctuary Border area on both sides of the fence, cover of midgrass, shortgrass, forb and shrub species groups significantly increased; total vegetation cover was similar between grazed and ungrazed areas. Cover of midgrasses was significantly higher in the Sanctuary (primarily due to increased plains lovegrass Eragrostis intermedia). No such differences were apparent for the other species groups. Blue grama Bouteloua gracilis became the most abundant species on livestock grazed and non-livestock grazed areas.
Observations of vegetation cover increases (in both grazed and ungrazed transects) suggest that longer-term changes in vegetation may be occurring due to factors other than livestock grazing (e.g. precipitation).
As well as increases in plant species diversity observed in the Sanctuary, diversity of animal groups studied (birds, small mammals and grasshoppers) also increased subsequent to livestock removal.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:
https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume42/Number4/
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