Size and Biomass Relationships for Five Common Northern Chihuahuan Desert Plant Species (General NOTES‪)‬

Allometric equations are commonly utilized to estimate plant biomass from measured species attributes such as height, canopy width, and root collar diameters. These same attributes are also commonly measured as part of plant community surveys where they may be used as stand alone variables to determine dominance within a community. Published allometric relationships that estimate biomass from plant size and shape for desert plants (Smith & Ludwig 1976; Neuenschwander et al. 1978; Felker et al. 1982; Hughes et al. 1987) are mostly limited to dominant or agriculturally important species. The scarcity of allometric equations coupled with the diversity of desert plant species make estimation of biomass accumulation and productivity difficult (Navar et al. 2001). Therefore, more information is needed on plant size and biomass relationships in order to refine plant production estimates in deserts for conservation of plant communities and wildlife. Allometric equations were developed for several common Chihuahuan species for the purpose of estimating standing crop from plant characteristics typically collected in plot surveys. Maximum height, basal diameter (root collar at ground surface or grass clump in the case of Bouteloua ramosa), and maximum canopy diameter were measured for five species during May 2000. At Big Bend National Park (BBNP), two to three samples of B. ramosa and Agave lechuguilla were harvested at four different sites for a total of ten plants per species. Plants were clipped at ground level. However for A. lechuguilla, roots 1 mm in diameter (estimated visually) were also harvested by carefully excavating soil beneath the plants with a shovel and gently removing soil from the roots by hand. In general, root systems of A. lechuguilla were found to be shallow with lateral roots extending two to three times the width of the plant canopy. The four sites were mostly homogeneous, characterized as lowland grass and shrub communities. Canopy cover measured for the sites was variable, ranging from 17 to 76%. All samples for each species collected were pooled for statistical analysis (S-Plus, MathSoft, Inc., Cambridge, Massachusetts).