Wild and Free-Roaming Horses and Burros Current Knowledge and Recommended Research. (1980) / Chapter Skim
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EFFECTS OF EQUIDS ON OTHER ECOSYSTEM COMPONENTS
EFFECTS OF EQUIDS ON OTHER ECOSYSTEM COMPONENTS
Pages 131-171
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From page 131... ...
Each land unit is capable of carrying some potential array of vegetative species if not excessively disturbed. As recognized and defined in PL 95-5l4, the "range condition" on a site at any point in time is "the present state of vegetation...in relation to the potential plant community for that site, and the relative degree to which the kinds, proportions, and amounts of vegetation in a plant community resemble that of the desired community for that site." To establish and maintain some level of range condition would appear to be a desirable management goal for each land unit.
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From page 132... ...
4. Impacts on range nutrition and feeding ecology created by wild equids and associated domestic and native ungulates.
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From page 133... ...
suggested that under the Wild and Free-Roaming Horse and Burro Act of l97l, horses and burros living in areas where a year-round forage supply was unavailable would cause serious range deterioration that would lead to reduced grazing capacity for wild ruminants and domestic livestock. Subjective observations such as the foregoing are generally based on years of professional experience and may possibly depict the reality of the horse and burro problem.
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From page 134... ...
studied burros in Bandelier National Monument and concluded that foraging by a population estimated to number from l07 to l20 individuals had led to degradation of some 4,000 ha of rangeland. He postulated the following order of disappearance of perennial grasses in pinyon-juniper communities overgrazed by burros: (l)
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From page 135... ...
There is also a need to monitor range impacts with greater sensitivity than is presently possible with existing techniques, which were developed largely for use with domestic livestock. Since scientific information on specific grazing impacts by wild horses and burros is scarce, additional perspective may be gained through exploration of the relatively extensive literature on grazing impacts by livestock.
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From page 136... ...
This table summarizes a small sample of long-term grazing experiments that have either been conducted in plant-community types where wild horses now occur, or that have focused on plant species locally important elsewhere on wild horse ranges. No comparable studies were found that dealt with the blackbrush-grass or Mojave desert scrub vegetation types now occupied by feral burros.
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From page 137... ...
) Use Stocking Rates tAUD/acrelLight Moderate Heavy Key Forage Species Plant Utilisation Levels t%)
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From page 138... ...
Given comparable stocking rates, differences in precipitation notwithstanding, declines in range condition in the Oregon study would likely have been larger. Even with the prevailing conditions observed, the important species elk sedge (Carex geyeri)
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From page 139... ...
showed that heavy spring grazing of sagebrush-bunchgrass range by sheep in Idaho led to a deterioration of range conditions, including replacement of bluebunch wheatgrass (Agropyron spicatum) by annual cheatgrass (Bromus tectorum)
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From page 140... ...
During wet years, grazing capacities of the two ranges were similar, but in dry years, they were 60 percent less on the cheatgrass range. Thus, maintenance of plant communities with a major component of perennial vegetation appears desirable not only from the standpoint of long-term site stability, but also from the viewpoint of a dependable forage supply for grazing animals.
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From page 141... ...
It is not stretching the correspondence between concept and reality too far to suggest that interspecific competition can be created by administrative fiat. If the decision is made to limit the number of grazing animals on a given tract of land to a certain number of animal unit months (AUM: see Table 3.l for definition)
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From page 142... ...
The important point may be whether sheep are sufficiently wideranging to be unaffected by the burro vegetation damage close to water holes (which most authors agree takes place) , or whether vegetation consumption and alteration extend far enough out from water holes to affect appreciable fractions of sheep home ranges.
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From page 143... ...
In the desert scrub vegetation of the Tonto Platform and Rampart Cave area, where burro use was intermediate, rodents were more numerous in the impact than in the control area, and were composed in large part of disturbance species in the family Cricetidae. In the riparian-plant community of the canyon's inner gorge, where burro use was heavy and vegetation damage extreme, rodent populations in the impact areas were far smaller than those in the control plots.
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From page 144... ...
describes a situation in the White Mountains on the California-Nevada border. Up to 25 years ago, when wild horses were scarce in the region, bighorn sheep occupied all parts of White Mountain Peak, which rises to l4,000 feet, including the foothills on the east side of the mountain.
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From page 145... ...
However, information is available on livestock grazing impacts, which should be similar to those wild equids. The following review deals with the influence of livestock grazing on vegetation, soil, infiltration, and water-quality parameters.
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From page 146... ...
found midgrass standing crop to be similar on moderately, continuously grazed and short-term grazed pastures (Figure 3.l)
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From page 147... ...
l47 To o o CM nr o o U)
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From page 148... ...
Wood's (l979) study in Rolling Plains, Texas reported organic matter to be highly correlated with infiltration rates and sediment production, but found little difference due to grazing treatment.
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From page 149... ...
These data were also used in developing a deterministic model for predicting infiltration rates under various livestock grazing regimes (Gifford and Hawkins l978, Hawkins and Gifford l979)
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From page 152... ...
l52 tn *
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From page 153... ...
. FIGURE 3.2 Relationships between infiltration rates (f )
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From page 154... ...
The impact of grazing on infiltration rates will vary depending on range condition. Generally, infiltration rates of a site improve as the site's range condition improves (Osborn l952, Rauzi and others l958, Leithead l959, Rauzi l960, Johnston l962, Rhoades and others l964)
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From page 155... ...
l55 -5 2 O M i CO i to 8 i to 1 o o tT)
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From page 156... ...
Dotted portions of each curve represent time periods after l0 minutes when an interaction between rock cover and trampling existed.
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From page 157... ...
Dotted portions of each curve represent time periods after 15 minutes when an interaction between grass cover and trampling existed. (From Dadkhah and Gifford, unpublished manuscript.)
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From page 158... ...
studied the influence of short-term; moderate, continuous; and very heavy, continuous grazing on sediment production at Edwards Plateau, Texas. He found no difference in sediment production between moderately, continuously grazed pastures and those grazed for a short amount of time (Figure 3.6 and 3.7)
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From page 159... ...
l59 N « sID s K I en «0 1 Sl CD Sc i•l- 4-> to OL Vt OJ « g.
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From page 160... ...
l60 o> Nouonaoyd (VH/SNOi)
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From page 161... ...
studied the influence of deferred rotation; rest rotation; moderate, continuous grazing; and no grazing on riparian habitat in the Blue Mountains, Oregon. He found that overwinter effects were more extreme than could be accounted for by livestock grazing.
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From page 162... ...
Bacteriological counts in runoff from both grazed and ungrazed pastures generally exceeded recommended water-quality standards. Runoff from the grazed pasture contained 5 to l0 times more fecal coliform than runoff from the ungrazed pasture.
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From page 163... ...
They found no detectable increase in coliform counts due to livestock grazing. Observed increases in bacteriological counts were due mainly to natural causes.
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From page 164... ...
To plan effective grazing management programs, the range manager needs to know more than merely which plant species are consumed or preferred by his grazing animals and the extent to which their diets overlap. He must also understand the temporal and spatial patterns of such grazing use, the relative degree of foliage removal on the major forage plants in the community, and the parts of various plants that are consumed.
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From page 165... ...
The actual size of these pastures will depend upon the present grazing capacity of the areas selected for study and the seasons and durations of the grazing periods.
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From page 166... ...
The stocking rates should be determined through consultation with professional range managers and scientists (BLM, USFS, Soil Conservation Service [SCS] , and university scientists and extension specialists)
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From page 167... ...
Likewise, few data have been recorded on the influences grazing livestock have on range hydrology for the western rangeland now supporting wild equids. To plan effective management programs, the rangeland manager needs to know the impact of wild equids, livestock, and/or wildlife on hydrologic parameters.
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From page 168... ...
The rainfall application rate should exceed infiltration rates, and raindrop size and terminal velocities should approximate a natural storm of the intensity simulated. A minimum of three runoff plots should be used per grazing treatment and vegetation-soil unit sampled.
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From page 169... ...
The following data should be collected from each runoff plot: Infiltration rate Sediment production Vegetational cover by species Bare ground cover Microtopography Soil bulk density Soil organic matter Soil aggregate stability Grass standing crop.
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From page 170... ...
Methodology The design of this study will depend to some extent on whether the grazing animals are using springs, established water holes, or live streams as a source of water. It would be desirable, if possible, to include riparian zones with the headwater originating in the pastures and in relatively good biological condition.
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