Graduate Thesis Or Dissertation
 

Plant community and soil relationships on some rangelands of northeastern Nevada

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  • Relationships between sagebrush-dominated plant communities and soil-site characteristics were examined on 372 relatively undisturbed rangeland sites of the Humboldt National Forest, in northeastern Nevada. Plant species production data were analyzed by TWINSPAN to develop a hierarchical, floristic-based community type (C.T.) classification. Seventeen C.T.s were identified in this analysis and named by their dominant shrub and grass species. Shrub species were more effective than grass species, which in turn were more effective than forb species in discriminating between C.T.s. Soil temperature and moisture data, collected between 1983 and 1986 on 35 rangeland sites, indicated that aridic soil moisture regimes dominated the study area. The average number of days when soil temperature and moisture were not limiting to plant growth ranged from 28 days on Artemisia arbuscula sites to 70 days on mixed mountain brush sites. Soil temperature and moisture parameters were effective in discriminating between most plant C.T.s, yet their effectiveness varied considerably among types. Soil physical and chemical properties were examined at each of the rangeland sites used in the TWINSPAN analysis. The C.T.s identified in that analysis followed an apparent gradient of increasing soil fertility. A. nova C.T.s commonly occupied the lowest fertility sites. Moderate soil fertility sites supported A. arbuscula, A. longiloba, and A. tridentata ssp. wyomingensis C.T.s. Artemisia tridentata ssp. tridentata and ssp. vaseyana C.T.s occurred on sites with the highest soil fertility levels. Discriminant analysis indicated that 68 percent of the rangeland sites sampled could be correctly assigned to their appropriate C.T. based upon soil and site properties. The percent of sites correctly classified ranged from 25 percent within the A. tridentata ssp. tridentata/Festuca idahoensis C.T. to 100 percent in the A. longiloba/ F. idahoensis C.T. Soil and site factors most useful in discriminating between C.T.s were mollic epipedon thickness, elevation, subsoil clay content, total rock content, percent slope, and total soil depth. This method of relating individual soil and site factors to vegetation provides a useful approach for testing the validity of floristic based ecosystem classifications.
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