Statistical analysis
The importance value of each tree, shrub and herb in each
plant plot was calculated with the following formulas
(Zhang and Oxley, 1994):
Tree IV ¼ ðRDen þ RF þ RDomÞ=300 (1)
Shrub-Grass IV ¼ ðRDen þ RF þ RCÞ=300 (2)
where Tree IV is the tree importance value, RDen is the
relative density, RF is the relative frequency, RDom is the
relative dominance, and RC is the relative coverage.
Species diversity indices were determined (Ma et al.,
1995) as Shannon–Wiener’s index of diversity
H ¼ ΣPi lnPi (