| Table 6. The comparison of the results using the optimal models without and with the original Hegyi and improved Hegyi_I involved for sunny-steep, sunny-gentle, shady-steep and shady-gentle slope forests (a, b, c, f and g are model parameters; STE is the standard error of the estimated parameter; RMSE and R2 respectively are root mean square error and coefficient of determination between the observed and estimated values of H; SSR is the sum of squared residuals; and the symbol * implying the model parameter statistically is significantly different from zero at the significant level of 0.05). | ||||||||
| Model characteristics | Model parameter | Model evaluation | ||||||
| a (STE) | b (STE) | c (STE) | f (STE) | g (STE) | RMSE | SSR | R2 | |
| Sunny-steep slope | ||||||||
| *4.253(0.362) | –0.249(0.908) | 1.341 | 154.550 | 0.622 | ||||
| *10.198(0.906) | –0.921(1.083) | 0.071(0.063) | 1.330 | 152.192 | 0.628 | |||
| *3.693(0.463) | 1.712(1.367) | *–0.182(0.086) | 1.312 | 148.219 | 0.638 | |||
| Sunny-gentle slope | ||||||||
| *16.817(0.924) | *1.591(0.178) | *0.109(0.019) | 1.444 | 200.078 | 0.754 | |||
| *16.858(0.981) | *1.542(0.283) | *0.107(0.022) | 0.006(0.026) | 1.443 | 199.967 | 0.754 | ||
| *17.259(0.967) | *1.119(0.130) | *0.093(0.016) | *0.015(0.004) | 1.348 | 174.524 | 0.786 | ||
| Shady-steep slope | ||||||||
| *4.094(0.195) | *0.359(0.017) | 0.834 | 73.031 | 0.818 | ||||
| *4.415(0.245) | *0.339(0.018) | *–0.022(0.009) | 0.811 | 69.059 | 0.828 | |||
| *4.864(0.279) | *0.316(0.018) | *–0.017(0.004) | 0.759 | 60.472 | 0.849 | |||
| Shady-gentle slope | ||||||||
| *14.119(0.581) | *2.184(0.355) | *0.169(0.026) | 1.356 | 255.579 | 0.706 | |||
| *14.301(0.645) | *1.928(0.402) | *0.162(0.029) | –0.298(0.250) | 1.363 | 258.098 | 0.703 | ||
| *13.906(0.504) | *2.850(0.569) | *0.191(0.027) | *–0.044(0.021) | 1.341 | 249.868 | 0.712 | ||