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Microtopography and Grazing in Desert Range Land: A Lesson in Statistics Versus Reality in the Field

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Abstract:This presentation summarizes two experiments on the effects of grazing on soil microtopography in a Chihuahuan Desert rangeland. In the first experiment, we measured the effect of three consecutive years of short duration <48 hours per year) intense grazing (20--40 yearling cows per hectare) and shrub removal on microtopography. Microtopography were measured in 18 plots (treatments). Treatments were a combination of two factors: (I) three levels of grazing (winter-grazed, summer-grazed, and not grazed), and (2) two levels of habitat structure (shrubs-removed and shrubs-intact). Mesquite (Prosopis glandulosa) shrubs were removed from half of the plots (9 out of 18 plots ). In the second experiment, three grazing gradients from water point, measurements were made using a modified erosion bridge at three distances (50 m, 450 m, and 1050 m) from water points.

From Experiment I, we found that the average height of the micromounds, the average depths of intermound depressions, and the number of micromounds were significantly reduced on the grazed plots. There were significant differences in average micromound heights and intermound microdepression depths attributable to the season of grazing. Microtopography was significantly reduced on grazed plots from which shrubs were removed, compared to ungrazed plots, and grazed plots with shrubs present. Grass canopy reduction, and destruction of the micromound structure in a short duration, plus intense grazing, results in erosion of micromounds and in-filling of intermound depressions. The loss of microtopography coupled with reduction in vegetation height and cover resulting from short.
From Experiment 2, we found that microtopography of plots at 450 m from water was not significantly different from that recorded at 50m. Microtopography of plots that were 1050 m from water points was significantly different from that of plots nearer water points. Strong correlation between microtopography and the cover of long-lived perennial grasses (R 2 = 91% ) was found, such dependence could be used assessing the trend in organic matter content that is in concordance with that of microtopography .Loss of microtopography from the impact of livestock in biospheres exacerbates erosion processes and contributes to desertification.
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Citation:Nash, M. S. Microtopography and Grazing in Desert Range Land: A Lesson in Statistics Versus Reality in the Field. Presented at Landscape Ecology Branch (LEB) Seminar Series, Las Vegas, NV, November 12, 2003.
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Contact: Chris Siebert - (702) 798-2234 or siebert.christopher@epa.gov
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Division: Environmental Sciences Division
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Branch: Landscape Ecology Branch
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Product Type: Abstrct/Oral
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Presented: 11/12/2003
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Related Entries:
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Bullet Item Landscape Indicators of Surface Water Conditions
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