Allometric Equations for Predicting Above-ground Biomass of Tamarix in the Lower Colorado River Basin

Abstract

Allometric equations are essential for quantitative study of aboveground biomass. The paper presents an effort in acquisition and validation of allometric equation for salt cedar (Tamarix spp.), a species that has been criticized for its invasion and negative impacts on the riparian ecosystem in the western United States. In the summers of 2009 and 2011, biomass destructive samplings were conducted to harvest and collect salt cedar samples at Cibola National Wildlife Refuge, Arizona. The allometric equations were developed by establishing the relationship between aboveground biomass with average basal diameter, tree height, and total basal area. The validity and the strength of the allometric models were examined with the adjusted coefficient of determination (r²), standard error of estimate (SSE), and Akaike Information Criterion (AIC). Total basal area was identified as the best predictor for salt cedar biomass, followed by tree height. Average basal diameter was a poor predictor. In linear equations, total basal area accounted for 78.4 percent of the total variation in aboveground biomass. In logarithmic equations, tree height and total basal area together explained 87.7 percent and yielded the small AIC and SSE. These equations will advance the quantitative estimation of salt cedar biomass and provide useful information for studying evapotranspiration, water consumption, and carbon storage.