[Effects of different removal disturbance intensity on plant diversity of Bursaphelenchus xylophilus-invaded Masson pine community].

The study on the plant diversity of Bursaphelenchus xylophilus-invaded Masson pine community under effects of different removal disturbance intensity showed that the species diversity indices (richness, Shannon-Wiener index and evenness) of arbor layer decreased in the sequence of broad-leaved stand after the removal of all infected pine trees in the pure pine stand in Fuyang > lightly infected Masson pine - Schima superba mixed stand in Fuyang > uninfected stand mixture of Masson pine and Castanopsis fargessi as the control > lightly infected pure Masson pine stand in Fuyang > Quercus variables stand formed after selective removal of infected pine trees from a mixed Masson pine and Q. variables stand in Zhoushan Islands > pure young Masson pine stand formed after the removal of all infected pine trees from a pure Masson pine stand > pure Liquidambar formosana stand after the removal of infected pine trees from a pure pine stand in Zhoushan Islands > mixed stand consisted of Pinus thunbergii and the Masson pine in Zhoushan Islands > moderately infected Masson pine stand in Zhoushan Islands. All the three indices of shrub layer did not show any significant differences among different communities, except for the pure pine stand in Zhoushan Island, which were the lowest. The three indices of herb layer were higher in pure young Masson pine, Q. variables stand, and L. formosana stand than in other stands. The Masson pine forest at different geographical situation and with different harm extent had distinct disparity, as well as that in different disturbance degree and restoring manner. The "Index of Disturbing Intensity of Stump and Fallen Woods" or IDISF was created to represent the disturbance degree of tree removal on plant diversity. It was found that for both less and more removal disturbing degree, the relationship between species diversity indices and IDISF followed the "Mid-altitude bulge" theory. Specifically, both excessive and insufficient removal of infected trees would cause the decline of plant species diversity in certain degree. Covariance analysis of IDISF indicated that different IDISF had no significant effects on the species diversity of arbor layer, but had different effects on that of shrub and herb layers, which could be used to assess the changes in species diversity of different Masson pine communities after the invasion of pine wood nematode.