Species variables or environmental variables as indicators of forest biodiversity: a case study using saproxylic beetles in Maritime pine plantations

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Table II

Results of PLS regressions with deadwood volume and diversity variables as predictors of the species richness of saproxylic beetles (RMSEP: root mean squared error of prediction).

Minimum diameter	Models	Nb of variables	RMSEP	R²	P
1 cm	All independent variables	34	6.2	0.74	0.941
	Important variables (VIP > 1)	14	5.2	0.72	< 0.001
	Diversity variables	4	6.2	0.57	< 0.001

10 cm	All independent variables	23	5.8	0.74	0.080
	Important variables (VIP > 1)	12	5.4	0.69	< 0.001
	Diversity variables	4	5.8	0.62	< 0.001

15 cm	All independent variables	20	5.7	0.75	0.066
	Important variables (VIP > 1)	10	5.4	0.68	< 0.001
	Diversity variables	4	5.4	0.68	< 0.001
	Diversity variables without decomposition class No. 1	4	5.7	0.63	< 0.001
	Diversity variables without decomposition class No. 2	4	6.5	0.54	< 0.001
	Diversity variables without decomposition class No. 3	4	5.9	0.63	< 0.001
	Diversity variables without snags	2	5.8	0.64	< 0.001
	Diversity variables without stumps	2	6	0.57	< 0.001
	Diversity variables without downed dead wood	2	6.4	0.56	< 0.001

20 cm	All independent variables	13	6.6	0.56	0.021
	Important variables (VIP > 1)	8	6.3	0.59	< 0.001
	Diversity variables	4	6.4	0.55	< 0.001