Distribution Pattern And Determinants Of Species And Functional Diversity Of Woody Plants In Zhoushan Islands

Biogeographic patterns and driving mechanisms of species diversity and functional diversity are important for biodiversity conservation and ecosystem function restoration.As a special biogeographic region,islands are rich in biological resources.It becomes a natural laboratory to test the theory of biogeography and ecological evolution.According to the classical theory of island biogeography,island area and distance from the mainland are the key factors influencing the biodiversity of islands.Some studies have shown that both species diversity and functional diversity are affected by factors such as climate.At present,there are few studies on the distribution pattern and driving mechanism of island species diversity and functional diversity in the context of intense human activity.We used the abundance data of woody plants in 47 islands in Zhoushan region,including 107 plots investigated by the statistical sample method and 262 plots investigated by the typical plot method.Eight functional traits were measured,including tree height,specific leaf area,mean leaf area,leaf dry matter content,specific twig length,twig water content,twig wood density,and Huber value.The island area was derived from the Chinese island record,and the distance from the mainland was collected to extract climate data(annual average temperature,water vapor pressure,wind velocity and aridity index)from corresponding sites.Besides,remote sensing images were used to interpret land use types of islands and quantify the intensity of human disturbance.On this basis,we discussed the biogeographic patterns and influencing factors of island woody plant species diversity and functional diversity.First,Pearson's correlation analysis was used to test the relationship between all variables.Then,multiple regression analysis and variance decomposition were used to further reveal the impacts of island attributes,climate factors and human disturbance intensity on species diversity and functional diversity and the relative importance.The main results are as follows:(1)The biogeographic pattern of species diversity of island woody plants conformed to the theory of island biogeography,that was,the species diversity increased with the island area and decreased with the distance from the mainland.Besides,the distribution of evergreen and deciduous species was not significantly correlated with island area(p>0.05),and there was a significant positive relationship between the deciduous tree species in forests and the closest distance from the mainland(p<0.01).(2)The distribution of species diversity of island woody plants was significantly affected by aridity index(p<0.001),less affected by wind velocity.Species richness increased significantly with human disturbance intensity(p<0.001).In forests,the proportion of deciduous species was low(p<0.001),the drier the island,the more the distribution of deciduous tree species.Besides,human disturbance caused more deciduous tree species to renew in shrub.(3)Island species diversity was primarily affected by distance from the mainland and was also limited by drought.The distance from the mainland and the wind mainly affected the distribution of deciduous tree species in forests.Species diversity and distribution of evergreen and deciduous species on the islands were not affected by human disturbance(p>0.05).(4)The functional diversity of islands was also positively correlated with the island area and negatively correlated with the distance from the mainland.In larger islands,evergreen plants with higher tree height and denser twig and lower water content were more common.The remote islands were dominated by the deciduous plants with lower twig density,higher leaf area,and twig water content.(5)The functional diversity of island woody plants decreased significantly with wind and drought(p<0.001).In the islands with higher wind velocity and drier habitats,plants had lower tree height and leaf area,and larger leaf dry matter content.The functional diversity also increased with the human disturbance intensity,and islands with greater human disturbance had more evergreen trees.(6)The functional diversity of island woody plants was mainly affected by island attributes and climatic factors.Among them,the functional diversity of shrubland was easily affected by drought.Community functional composition was mainly driven by climate,such as wind and drought,which had significant effects on leaf traits and tree height.The specific twig length and huber value of shrub were affected by the distance from the mainland.The results showed that the diversity distribution of woody plants in Zhoushan islands still conformed to the classical theory of island biogeography under the condition of severe human disturbance.Island area and distance from the mainland were the main determinants of species diversity of woody plants in Zhoushan islands.Functional diversity of woody plants in Zhoushan islands was mainly affected by island area,distance from the mainland,wind and drought.Community functional composition was most affected by wind and drought,and human disturbance had no significant effect on the distribution pattern of island species diversity and functional diversity.