Soil Stability Requirements for the Gallatin Elk Winter Range

Packer, Paul

Objectives of a study, begun in 1956, in the Gallatin River valley in Montana on a winter range grazed by elk (Cervus canadensis) were: (1) to determine the effects, on plant cover and soil conditions, of seeding and protection from elk grazing; and (2) to develop useful soil stabilization criteria for watershed protection. Plots were installed to measure ground cover density, soil bulk density, and soil eroded by high-intensity rainfall. Some plots were protected from elk use by fencing; others remained exposed. Some protected and unprotected plots were seeded to a mixture of grasses; others were not. Some grazed and seeded plots exhibited and retained nearly pristine plant cover (average density 97 percent) and soil conditions because surrounding natural snowdrift areas had prevented their use by elk. From 1958 through 1960, ground cover density increased from 26 to 73 percent on protected and seeded plots; from 33 to 62 percent on protected plots having native cover; from 24 to 52 percent on grazed and seeded plots, principally by stooling of plants; and from 26 to 33 percent on grazed plots having native cover. From 1959 through 1960, lowest bulk densities, 0.70 and 0.72, were found on the pristine plots. Bulk density on protected and seeded plots improved from 1.13 to 1.03; on protected plots having native cover, from 1.19 to 1.16; and on the grazed and seeded plots, from 1.40 to 1.25. Grazed plots having native cover deteriorated from 1.27 to 1.32. During the summers of 1959 and 1960, under the impact of six rainstorms having maximum 5-minute rainfall intensities of from 0.80 to 1.80 inches per hour, the amount of the eroded soil on the plots increased rapidly as the ground cover density decreased below 70 percent and as the bulk density of the soil increased above 1.04 g/cc. Erosion increased with increased intensity of rainfall, accelerating most rapidly on sites having less than 70 percent ground cover. Conclusions drawn from this study are: (1) protection from elk grazing followed by seeding has effected plant cover and soil improvements on the experimental plots; (2) management objectives for restoring and maintaining soil stability on this elk winter range include ground cover densities of at least 70 percent and soil bulk densities no greater than 1.04 g/cc; and (3) these objectives are expected to remain relatively stable even under the impact of higher rainfall intensities.

Soil Stability Requirements for the Gallatin Elk Winter Range

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