Estimating Twig and Foliage Biomass of Sagebrush, Bitterbrush, and Rabbitbrush in the Great Basin

Abstract

Shrub crown characteristics useful in regression equations for predicting two biomass components (annual production and fine fuels) were identified for six shrubs common to the Great Basin. Shrub characteristics most useful in these equations were maximum and minimum crown diameter, and crown denseness and depth. Prediction equations were developed for each species or subspecies included in this study. Additionally, biomass equations were developed for combined species or subspecies of morphological similarity within the Artemisiu genus. As early as 1958, Evans and Jones addressed the practical importance of a method for determining forage production in which clipping or mowing was not necessary. Since then, much attention has been directed toward developing methods for predicting shrub production from easily measured crown dimensions. Volumetric or crown area relationships based on crown height and diameters have been described for serviceberry (Amelanchier alnifolia) by Lyon (1968), for eight Chihuahuan desert shrubs by Ludwig et al. (1973, and for big sagebrush (Artemisia tridentata wyomingensis) by Rittenhouse and Sneva (1977). Brown and Marsden (1976) and Alexander (1978) developed equations for predicting fuel loadings from height and percent crown cover measurements. Various stem diameter measurements were used as biomass predictors by Ohmann et al. (1976), Brown (1976), and Grigal and Ohmann (1977). Davis et al. (1972) related forage production to ring widths for several salt desert shrub species. Thus, the value and practicality of such methods has been well documented. The sagebrush taxon, Artemisia, constitutes the most abundant and widespread shrub component of ecosystems in the Great Basin and provides a source of food and cover for livestock and wildlife. Taxonomic difficulties exist within this genus at the species, subspecies, and variety levels. Although ecological differences have been described (Winward and Tisdale 1977), field identification of sagebrush species is often difficuh to determine. This is especially true between low and black sagebrush (A. arbuscula and A. nova) and the subspecies differentiations for big sagebrush (A. tridentata ssp. tridentata, A. tridentata spp. vaseyana, and A. tridentata spp. wyomingensis). A reliable dimension analysis technique for determining canopy biomass components in which species differences were not necessary would expedite field data collection and data analysis procedures. The primary objective of this study was to identify shrub crown characteristics which could be used to predict two shrub biomass components (annual production and fine fuels) and to formulate reliable prediction equations from these characteristics. The seconAuthors are research assistant and assistant professor, Renewable Natural Resources Division, University of Nevada Reno, 1000 Valley Road, Reno, Nevada 8951% and research forester, Intermountain Forest and Range Experiment Station, Renewable Natural Resources Center, 920 Valley Road, Rena, Nevada 89512. This research represents the contributions of the Nevada Agricultural Experiment Station Journal Series Number 446. Financial support from the IntermOUntain Forest and Range Experiment Station is acknowledged. dary objective was to evaluate the reliability of the prediction equations when shrub species of similar form were grouped together. Methods and Procedures Fifty-nine study sites were selected to represent the major shrub communities associated with the pinyon-juniper vegetation in the Great Basin. The study included the following taxa and number of sample shrubs: Artemisia tridentata tridentata (n=lO) ARTRTR Basin big sagebrush Artemisia tridentata vaseyana (n=54) ARTRVA Mountain big sagebrush Artemisia tridentata wyomingensis (n=50) ARTRWY Wyoming big sagebrush