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Show I U. K. Range Management Practices III. K. 1. Statement of the problem. Grazing is legislatively authorized throughout Glen Canyon National Recreation Area. Forty grazing allotments on the NRA are used by 75 permittees, and virtually all of the allotments pre- date the establishment of Glen Canyon NRA by many years. Allotments include about 80 percent ( 980,000 acres) of the land surface of the NRA, with an authorized use of 26,500 licensed animal unit months ( AUM). ( An AUM is a measure of the amount of grazing, in this case one cow and calf, on a range for one month.) Cattle are the predominant livestock species grazing on the NRA, although sheep formerly grazed in the area, feral horses are present in some canyons, and burros frequent portions of the NRA on the Navajo Reservation shore. Managed cattle allotments are typically used seasonally in fall, winter, and spring; also, most Glen Canyon grazing allotments extend beyond the park boundaries. In a few isolated areas, small numbers of unmanaged cattle that have escaped control of present or former permittees remain year- round. These animals are classified as feral cattle. Grazing leases are administered by the Bureau of Land Management ( BLM), using the same range management policies and procedures exercised on BLM- managed lands. In 1986, BLM and NPS agreed by Interagency Agreement to consult and cooperate to ensure that grazing management activities do not conflict with the management purposes of the NRA described in the unit's enabling legislation and General Management Plan ( NPS 1979). This requires that the National Park Service determine the potential effects of any proposed range management action on the values and purposes of the NRA. Range management practices potentially affecting water resources fall into four categories, as follows: • Land treatments-- Trees and shrubs are sometimes reduced on public ranges to increase forage production for cattle. Burning, chaining ( mechanical removal by drag chains), and herbicides are the most common land treatment methods. The effect on water resources results principally from lowered water retention and increased runoff. Sediment loads downstream may increase, especially during storms, and higher sediment loads may be deleterious where stream flow is sufficient to support benthic macroinvertebrates. If the treatment area is large, enough additional runoff may be generated to raise the magnitude of floods in downstream drainages, causing further ecosystem effects. The effect of herbicides on downstream waters is poorly documented. It is known, however, that herbicide residues are often present in water draining agricultural areas; such residues could therefore be expected in runoff from range areas where herbicides have been applied. Although the effects of a few discreet herbicide applications on rangeland may be transitory, caution is clearly needed, especially since some aquatic species are sensitive to low concentrations of some of the chemicals used ( Kosinski 1984; Nimmo 1985). 50 |
