Methods of modelling relative growth rate

Forest Ecosystems

Table 2 Characteristics and model statistics of four Sitka spruce ( Picea sitchensis (Bong.) Carr.) trees at Cefn Du (plot 1), Clocaenog Forest (North Wales, UK)

Tree #	*dbh* (cm)		b	c	Volume (m ³ )		Total height (m)		Stem diameter ( *dbh* )
Tree #	Min.	Max.	b	c	*Bias*	*RMSE*	m ₁	*RMSE*	m ₂	*RMSE*
2000	6.4	32.2	−0.05251	6.12877	0.00303	0.02478	2.82205	0.01309	1.07431	0.02211
3000	4.2	28.3	−0.05057	6.44977	0.00307	0.01646	2.63452	0.00633	1.04791	0.01835
4000	4.9	32.6	−0.04667	6.40575	0.00249	0.02401	2.78971	0.01296	1.13672	0.01294
5000	6.6	38.7	−0.00822	3.68512	0.00024	0.01248	2.66006	0.01105	1.17268	0.01218

dbh – stem diameter at breast height at 1.3 m above ground level; b, c – model parameter of the Chapman-Richards model of relative growth rate; m ₁, m ₂ – allometric coefficients for estimating the relative growth rates of total height and stem diameter, respectively. Bias and RMSE relate to estimates of relative growth rates.