Table 2. Correlation matrix between PWD occurrence and natural factors.

	Altitude	Slope	Distance to river	Mean Temp. from May to Aug.	Duration of sunshine	Distance to forest fire	Distance to fumigation pile	Distance to thinning forest	No. of infected dead trees
Altitude	1.0000
Slope	0.6546a	1.0000
Distance to river	0.0720*	0.0030*	1.0000
Mean Temp. from May to Aug.	−0.4643*	−0.1916*	−0.1618*	1.0000
Duration of sunshine	0.1925*	0.0306*	0.2458*	−0.3821*	1.0000
Distance to forest fire	0.0937*	0.1345*	0.0834*	0.0285*	0.0236*	1.0000
Distance to fumigation pile	0.0560*	0.0613*	−0.0071*	−0.1097*	0.1097*	0.2522*	1.0000
Distance to thinning forest	−0.2173*	−0.0507*	−0.0267*	0.1684*	0.0400*	0.0341*	0.1109*	1.0000
No. of infected dead trees	0.6862*	0.4595*	0.1315*	−0.5084*	0.4997*	0.1432*	0.1966*	−0.0750*	1.0000

Values with asterisk indicate a significant correlation at the 0.05 level.