Methods of modelling relative growth rate

Forest Ecosystems

Table 3 Characteristics and model statistics of four British Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco) yield tables (Edwards and Christie 1981 ) relating to initial spacing 1.7 m × 1.7 m and crown thinning

Yield class	dg (cm)		b	c	Volume (m ³ ∙ha ⁻¹ )		Top height (m)		Mean diameter ( d g)
Yield class	Min.	Max.	b	c	*Bias*	*RMSE*	m	*RMSE*	*RMSE*
24	12.8	76.7	−0.03240	5.68749	0.00011	0.00185	3.64234	0.00153	0.00658
18	12.2	60.9	−0.03147	5.65227	0.00014	0.00181	3.46283	0.00151	0.00560
12	12.4	43.5	−0.02988	5.43637	0.00004	0.00075	3.20122	0.00124	0.00793
8	11.7	32.5	−0.03095	6.16601	−0.00003	0.00072	3.06830	0.00092	0.00757

dg – quadratic mean stem; b, c – model parameter of the Chapman-Richards model of relative growth rate; m – allometric coefficient for estimating the relative growth rate of top height. Bias and RMSE relate to relative growth rates.