Study On The Invasibility And Resistance To Bursaphelenchus Xylophilus In Pine Forest Ecosystems

Bursaphelenchus xylophilus, one of most important invasive alien species around the world, can lead to lethal PNW (Pine Wilt Disease, Pine Wood Nematode) which quickly spread and heavily destruct pine forestry resources, nature landscape and ecosystem in China. There are myriad of literatures concern about its breakout mechanism and control measurement, and recently, some reports on the resistance mechanism of ecosystem against B. xylophilus's invade. However, few researches are carried out to study the resistance of post-invaded forest type against B. xylophilus's reinvade. This kind of research is valuable to reveal post-invaded succession dynamics and forest inventory and provide reliable reference for management.Two recovered ecosystem of P. mansoniana and P. thunbergii are chosen, and divided into 4 categories by the percentage of pine in the whole community: 1, pure (p>80%); 2, pine:hardwood (the pine mixed broadleaf forest with 7:3 ratio,6:4 ratio and 5:5 ratio). The impacts of B. xylophilus's reinvasion of different extents upon the 4 kinds of ecosystem community structure and function are analyzed. The results are following:(1) Influence on ecosystem community structure:the plant diversity (arbor, brush and herb) of pure forest are lower than that of mixed ones. The arbor diversity of P. mansoniana and P. thunbergii decreased suffering reinvasion of B. xylophilus. The brush diversity of pure P. mansoniana decreased while mixed one increased. The herb diversity shows inverse trend of the brush. When under slight invasion of B. xylophilus, the fluctuation range of mixed forest diversity was smaller than that of pure ones and the masson pine mixed broadleaf forest with 7:3 as well as 5:5 ratios are most stable. When under sever B. xylophilus stress, diversity of pure forest is most fluctuated, while the masson pine mixed broadleaf forest with 5:5 ratio and the black pine mixed broadleaf forest with 5:5 ratio are most stable ones. (2) Influence on ecosystem community function is reflected by diameter growth, volume growth and biomass:Diameter growth, volume growth and biomass of pure P. mansoniana and P. thunbergii are higher than those of mixed forests. When under B. xylophilus reinvasion, biomass of both kinds of pines decreased, the most stable ones are the masson pine mixed broadleaf forest with 5:5 ratio and the black pine mixed broadleaf forest with 5:5 ratio as well as, and the most fluctuated one is pure forests.(3) Influence on insect community: insect diversity of recovered P. mansoniana are higher than those of P. thunbergii; pure forests insect diversity are lower than mixed forests and phytophagous insect take the most part, parasitic ones the least. When under B. xylophilus reinvasion, insect diversity fall, and natural enemy increased, phytophagous group decreased. the masson pine mixed broadleaf forest with 5:5 ratio and the black pine mixed broadleaf forest with 5:5 ratio are the most stable, and pure forest are most fluctuated.In general, among forest types which formed by pine ecosystem resilience process, mixed ones are more resistant than pure ones not only in plants diversity, insect diversity but also in forest growth, biomass and community composition. In pure forest type, P. mansoniana is more resistant than P. thunbergii, while in mixed forests, the black pine mixed broadleaf forest with 5:5 ratio are most resistant. Understanding of forest spatial structure and mixed pattern with hardwood can guild artificial renewal.