Modelling the variation in wood density of New Zealand-grown Douglas-fir

New Zealand Journal of Forestry Science

Table 5 Parameter estimates for the model Eq. (1) to predict breast height outerwood density from age and MAT, with associated standard errors and tests of significance

Parameter	Estimate	Std. error	t value	p value
a, pre-1970 North Island	381.6	36.3	10.52	<0.0001
a, post-1969 North Island	217.5	91.9	2.37	0.018
a, South Island	195.0	24.5	7.95	<0.0001
b, pre-1970 North Island	5.5	3.2	1.74	0.082
b, post-1969 North Island	24.0	7.7	3.10	0.0021
b, South Island	27.1	2.4	11.19	<0.0001
c	355	71	4.98	<0.0001
d	0.0764	0.0114	6.70	<0.0001

The model explains 52.8% of total variance and has a root mean square error of 24.8 kg m⁻³