Additivity of nonlinear tree crown width models: Aggregated and disaggregated model structures using nonlinear simultaneous equations

•Developed crown width (CW) systems using nonlinear simultaneous equations (NSE).•Compared disaggregated and aggregated model structures and other additive approaches.•NSE accounted for inherent correlations among the CW components efficiently.•NSE ensured additivity properties of CW and its components models efficiently.•NSE with one-step proportional weighting system led to highest prediction accuracy.