Use of upper stem diameters in a polynomial taper equation for New Zealand radiata pine: an evaluation

New Zealand Journal of Forestry Science

Table 4 Diameter fit/prediction and volume prediction error statistics for the BASE, GB99 and M3_HABH taper models

Dimension	Model	Fitting data			Split-validation data			Independent-validation data
	Model	MB_dob (%)	MAB_dob (%)	RMSE_dob (%)	MB_dob/v (%)	MAB_dob/v (%)	RMSE_dob/v (%)	MB_dob/v (%)	MAB_dob/v (%)	RMSE_dob/v (%)
Stem diameters	BASE	0.143	4.254	5.802	0.696	4.313	5.788	1.603	5.060	7.052
	GB99	−0.429	3.561	5.208	−0.174	3.529	5.110	1.005	4.291	6.136
	M3_HABH	0.263	3.093	4.523	0.466	3.142	4.488	0.535	3.872	5.615
Total aboveground volume	BASE				1.133	5.515	7.720	1.371	5.322	7.408
	GB99				−1.316	3.768	5.247	0.525	4.683	6.372
	M3_HABH				0.768	2.729	3.824	−0.816	2.810	3.937
Volume to 14-cm top diameter (pulpwood volume)	BASE				0.784	5.328	7.553	0.707	5.092	6.989
	GB99				−1.586	3.671	5.153	−0.003	4.430	6.056
	M3_HABH				0.616	2.675	3.709	−1.232	2.863	4.140
Volume to 22-cm top diameter (sawtimber volume)	BASE				0.884	5.123	7.402	0.129	4.718	6.514
	GB99				−1.616	3.378	4.974	−0.472	4.038	5.697
	M3_HABH				0.763	2.861	3.982	−1.592	2.994	4.457

The percentages are based on the following overall means: (a) fitting data stem diameter means = 31.65 cm; (b) split-validation stem diameter means = 31.38 cm and tree volume mean = 2.528 m³ for total aboveground volume, 2.439 m³ for pulpwood volume and 2.310 m³ for sawtimber volume; and (c) independent-validation stem diameter means = 36.67 cm and volume mean = 3.649 m³ for total aboveground volume, 3.556 m³ for pulpwood volume and 3.429 m³ for sawtimber volume. The lowest MAB and RMSE values are shown in italics