Impact of Cattle Grazing and Summer and Winter Drought on Soil Mite Populations in the Northern Chihuahuan Desert

EPA Grant Number: U915582
Title: Impact of Cattle Grazing and Summer and Winter Drought on Soil Mite Populations in the Northern Chihuahuan Desert
Investigators: Taylor, Hilda S.
Institution: The University of Texas at El Paso
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 1999 through August 1, 2002
Project Amount: $85,124
RFA: STAR Graduate Fellowships (1999) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems


The objectives of this research project are to: (1) determine if soil mites can be used as bioindicators of disturbance and recovery in desert ecosystems; and (2) determine the impact of these disturbances on mites. The disturbances include multiple environmental (natural and anthropogenic) stressors. Investigations on how these stressors interact to impact desert soil ecosystems is essential to the development of adequate rangeland management practices, and to an understanding of desertification. Hypotheses will be tested using biodiveristy indices, population densities, and community composition comparisons.


This experiment was originally set up in 1993-1994 to investigate the effects of environmental stressors on ecosystem properties and processes, and is part of an Environmental Protection Agency (EPA) study of multiple stressors in arid ecosystems. The treatments are as follows: summer drought plots under "rain-out" shelters for the 4-month rainy season, winter drought plots under "rain-out" shelters for 8 months, and nutrient depletion. The plots are treated with glucose to stimulate microbial growth, which immobilizes the nutrients in the microbial biomass. Treatment through shrub removal includes cutting shrubs to the ground. Any sprouts are treated with herbicide. Livestock grazing is intense; it is at the rate of 40 head/hectare for 24 hours. The timing for fire-treated plots that were burned early in summer coincides with the first convectional storms of the year and the first potential for natural fire. The experimental design consists of a complete randomized block with six plots per block. The treatments have been assigned at random as the main effects in each of the blocks. Subplots (within each plot) have been assigned the following subtreatments at random: burn, nutrient depletion, burn and nutrient depletion control, winter rainout, summer rainout, and rainout control. The collection of soil mites was initiated on June 6, 1997, during the third year, which is the end of the exposure to the multiple stressor treatments, and is the beginning of the 3-year recovery period.

Expected Results:

This research project will show that multiple stressors will have a greater impact on soil biota than a single stressor. The results from this study can expand our understanding of the ecological processes in desert environments, and can be incorporated into technologies (methodologies) currently being used to manage and assess resource conditions in rangelands.

Supplemental Keywords:

soil mites, desert grasslands, cattle grazing, environmental stressors, desert soil ecosystems, anthropogenic stressors, natural stressors.

Progress and Final Reports:

  • 2000
  • 2001
  • Final