A growth-effective age-based periodic site-index for the estimation of dynamic forest site productivity under environmental changes

Table 5 Evaluation of the contributions of site index (\(SI\)) and periodic site index (\(pSI\)) in the periodic mean annual stand dominant height increment model (\(\Delta H\), Eq. 10) and in the volume increment model (\(\Delta V\), Eq. 11) using (i) the existing SI model of Assmann and Franz (1965) and (ii) the new SI model (Eq. 1) by splitting the data set into training (70%) and validation data (30%)

Sources	Eq.	SI	Training data				Validation data
Sources	Eq.	SI	\(R^2\)	\(RMSE\)	\(AIC\)	n	\(R^2\)	\(RMSE\)	\(AIC\)	n
Existing SI model	\(\Delta H\) (Eq. 10)	\(SI\)					0.743	0.097	−9964	5435
	\(\Delta H\) (Eq. 10)	\(pSI\)					0.793	0.087	−11,138	5435
	\(\Delta V\) (Eq. 11)	\(SI\)					0.428	5.022	33,002	5435
	\(\Delta V\) (Eq. 11)	\(pSI\)					0.471	4.829	32,578	5435
New SI model	\(\Delta H\) (Eq. 10)	\(SI\)	0.742	0.097	−6936	3804	0.744	0.096	−3006	1631
	\(\Delta H\) (Eq. 10)	\(pSI\)	0.812	0.083	−8135	3804	0.855	0.072	−3936	1631
	\(\Delta V\) (Eq. 11)	\(SI\)	0.442	4.917	22,932	3804	0.406	5.232	10,046	1631
	\(\Delta V\) (Eq. 11)	\(pSI\)	0.447	4.896	22,899	3804	0.433	5.112	9970	1631

R² Coefficient of determination, RMSE Root mean squared error, AIC Akaike information criterion, n Degrees of freedom

ISSN: 1297-966X