| Machilus thunbergii was the most widely distributed evergreen tree species in the islands of Eastern China.M.thunbergii community was one of main community types of zonal evergreen broadleaved forest in the islands of Zhejiang Province.However,little was known about this community due to lack of comprehensive investigation.A 1 hm2 M.thunbergii community fixed plot was established in Zhoushan islands.In the plot,all woody species at least 1cm in diameter at breast height were mapped,tagged,and identified to species,and their geographic coordinates were recorded following a standard field protocol.The niche characteristics and interspecific association of dominant species,species and functional diversity,community structure,floral characteristics and species composition were analysed.The results showed that there were 2030 genotype individuals,belonging to 39 species,39 genera,and 29 families.The flora displayed an apparent tropical characteristic,and there was a transitional characteristic from tropical floristic to temperate floristic element.The statistics of important value showed that M.thunbergii,Celtis sinensis,Liquidambar formosan,Zanthoxylum ailanthoides,Styrax confusus and Cyclobalanopsis glauca were dominant species.As a whole,the distribution of size class and height class of woody species in M.thunbergii community appeared as reverse "J shape".The age structures of C.sinensis populations were declining type.The age structures of L.formosan and Z.ailanthoide populations were stable type.The age structures of S.confusu and C.glauca populations were growing type.Shannon-Wiener index,Simpson index and Pielou evenness index of M.thunbergii community was 2.288,0.806,0.625.The major life form was deciduous tree species for adapting to strong wind,drought and barren environment.The major leaf-size class of community plants were small and medium leaves.The major flowering time of community plants were summer and spring.The major fruit type of community plants was drupes.The age structures of M.thunbergii populations were growing type.Individual mortality of M.thunbergii population was higher in middle and big size class.The niche breadth of M.thunbergii,C.sinensis,L.formosan were broader than other species,with Levins and Hurlbert' niche breadth values of 2.428,1.335,1.286 and 0.956,0.788,0.653,respectivelt,while Platycarya strobilacea,Lindera glauca,Maclura tricuspidata had narrower niche breadths.There were 22 species pairs with niche proportional similarity more than 0.5,accounting for 20.95%of the total pairs.The broader niche of two species had,the bigger of their niche proportional similarity was.The species with broad niche could had big niche overlap with another species with narrow niche.On the contrary,tne species with narrow niche could had low niche overlap with another species with broad niche.Significantly positive correlations existed among the 15 dominant species,which suggested that the community structure was stable.The X2 test showed that among the total 105 species pairs,2 species pairs exhibited significantly positive association and 2 species pairs exhibited significantly negative association.101 species pairs did not show significant association.The X2 test and association coefficient showed that species pairs with positive association were more than that with negative association.Therefore,the interspecific association of dominant species of M.thunbergii community in Zhoushan islands was relatively loose with certain independent at low extent.The community was close to climax community.Based on the through studies of community characteristics and species diversity,the succession and historical change of M.thunbergii community in Zhoushan islands was illustrated,which provided a scientific foundation for the restoration and management of the vegetation in Zhoushan islands. |
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