Validation of the Weibull-derived Gini coefficient for quantifying the inequality of the aboveground biomass...

The Gini coefficient (GC), derived from the Lorenz curve in economics, has been widely applied to quantify the inequality in biological size distributions. Although the GC can be theoretically obtained from distribution functions, previous studies have not cross-validated the distribution-derived GC with empirically determined GC values for important traits such as the aboveground biomass of plants. Here, we used aboveground fresh mass (FM) of >2800 culms from 50 bamboo species with 29-142 culms per species to test whether the FM, as a representative of aboveground biomass, adheres to a normal, log-normal, two-parameter Gamma, or two-parameter Weibull distribution, and compared the distribution-derived GC with the observed GC calculated using the polygon method (denoted as G_P ). The Gamma and Weibull distributions provided better fits for most species compared to the normal and log-normal distributions. However, the regression between the Weibull-derived GC and G_P was stronger and more robust than that between the Gamma-derived GC and G_P . This cross-validation between the theoretical and observed Gini coefficients confirms that the Weibull distribution is the best fit for bamboo FM data, and provides a validated inequality measure (i.e., the Weibull-derived GC) that may be extended to other clonal plants or monocultures exhibiting determinate growth (e.g., certain herbaceous crops), but further validation is needed for species with different life histories, particularly those with indeterminate growth.