Date of Award:

1-1-1977

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Advisor/Chair:

Gerald F. Gifford

Abstract

The objectives of this study were to 1) determine the effects of livestock grazing and periods of rest from grazing on infiltration and erosion rates of unchained woodland; chained, debris-in-place; and chained, debris-windrowed pinyon-juniper sites; and 2) utilize these measurements in developing guidelines for grazing management of pinyonjuniper rangelands that protect or improve the hydrologic condition of the watershed. The study was conducted on sandy loam soils in southeastern Utah during the summers of 1971 and 1972.

Runoff and erosion were artificially induced from small plots by simulating rainfall with the Rocky Mountain infiltrometer. Infiltration rates, erosion rates, and selected vegetative and edaphic parameters were measured on each plot. Forage removal by clipping and soil compaction subtreatments were applied to randomly selected plots in an effort to simulate the forage removal and trampling activities of livestock. Analysis of variance techniques were used to determine the effect on infiltration and erosion rates of forage removal and soil compaction subtreatment, grazing and varying periods of rest from grazing, and chaining treatments with similar grazing histories. Multiple regression techniques were used to evaluate the influence of vegetative and edaphic factors on infiltration and erosion.

Forage removal and soil compaction subtreatments had no consistent effect on infiltration rates. However, the clipping and compaction subtreatments were an instantaneous application of forage removal and soil pressure and thus may not adequately represent long term, accumulative conditions imposed by actual grazing.

Areas rested from livestock grazing since 1967 had significantly higher infiltration rates than grazed areas on unchained woodland and chained, debris-in-place sites. Grazed plots consistently had the lowest infiltration rates although this lower rate was not significantly different from infiltration rates measured on areas protected from grazing since 1969 or 1971. Grazing did not consistently affect infiltration measured on chained, debris-windrowed sites. Infiltration rates increased on all three vegetative conditions as the period of rest from grazing increased.

None of the 21 soil and vegetative variables included in this study were identified by multiple regression models as consistently explaining significant amounts of variation in infiltration rates. Results of this study indicate that the primary value of multiple

regression models is not to predict changes that will occur in infiltration because one management alternative is selected over another, but to help explain significant differences measured between treatments.

Erosion rates were not significantly affected by forage removal subtreatments, but a trend indicates that erosion increases on plots when above ground vegetation is removed by clipping. No consistent relationship between -erosion rates and soil compaction subtreatments was found.

A trend toward increased erosion rates on grazed areas was found. No consistent relationship between erosion rates and the various periods of rest from grazing was recorded. Thus, any rest from grazing appears to reduce the erosion potential from pinyonjuniper sites.

In summary, pinyon-juniper rangelands can be improved for livestock by chaining and seeding without causing a deterioration in watershed condition. However, to achieve these objectives, the sites to be treated must be carefully evaluated and the appropriate chaining, plant debris disposal, and seeding techniques identified. And following vegetative conversion, the areas must be properly grazed.

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