The Study On Plant Diversity And Regional Vegetation Characteristics In Coastal Hilly Areas On The East Of Hainan Island

The coastline of Hainan Island is about 1823 km,the eastern coast of it has plain sandy coasts,muddy estuary coasts and coastal hilly coasts from Mulantou in the north of Wenchang City to Meilian Village in the west of Sanya City,and the coastal hills are distributed with abundant plants of coastal tropical vegetation and elfin forest including coastal elfin forest,shrub forest and grass and so on.At the same time,the coastal hills are one of the areas with developed economy and frequent human activities,and the plant diversity in the coastal hills has also been negatively affected to a certain extent.In order to further protect the vegetation in the coastal hilly areas,and coordinate the relationship between protection and development,therefore,it is great practical and ecological significance to study on plant diversity and community characteristics in coastal hilly area on the east coast of Hainan Island.This study took the plant community in the coastal hilly area on the east coast of Hainan Island as the research object,and used the combination of route method and sample method to carry out field investigation.On this basis,the floristic composition of the community was compared and analyzed according to the traditional floristic method.Species richness index(d _GL),Shannon-wiener index(H),Simpson index(P)and Pielou's evenness index(E)were used to characterize plant diversity,and RDA analysis and Monte Carlo test were used to analyze the relationship between plant diversity and main environment factors.Then variance ratio method(VR)and M.Godron stability measurement method were used to explore the changing trend of community stability in time and space.Finally,X² test,Pearson correlation coefficient and Spearman's rank correlation coefficient were combined to explore the change characteristics of community interspecific relationship in time and space.The results were as follows:(1)The composition of coastal flora:there were 11,638 trees and shrubs(2.50 hm²) with height?1.5 m in the coastal hilly area of the east coast of Hainan Island,belonging to 69 families,219 genera and 361 species,the distribution types of families and genera on the east coast were diverse,the geographical elements of the flora were complex and tropical nature was strong,and the proportion of tropical genera increased gradually along the latitude from north to south.No matter in the eastern coast or in each region,the dominant species of the community were obvious,and there were both similarities and differences among the dominant species in different regions,and the species similarity was higher in the areas close to each other.(2)The relationship between plant diversity and main environmental factors:on the whole,the plant diversity index of coastal hilly area on the east coast of Hainan Island was 4.806,which was similar to that of tropical montane evergreen forest(4.87)in Bawangling National Nature Reserve on Hainan Island.From the perspective of each region,the diversity level of the five cities and counties were similar,Wenchang City was slightly higher,Qionghai City was the second,Sanya City was the third,Wanning City was the fourth,and Lingshui County was the lowest.And the RDA analysis and Monte Carlo test of diversity and topographic factors further showed that the response of plant diversity to topography was different in different regions,but altitude(P=0.002,F=17.3)and slope(P=0.04,F=4.9)were the most important topographic factors affecting plant diversity on the east coast,and diversity was positively correlated with altitude and negatively correlated with slope.The relationship between plant diversity and hydrothermal factors indicated that plant diversity in coastal hilly areas on the eastern coast of Hainan Island was significantly positively correlated with annual precipitation(P=0.011),while negatively correlated with annual average temperature(P=0.033).Although the responses of plant diversity to hydrothermal conditions were different in different regions,the responses of plant diversity in coastal areas to annual precipitation were similar,that was,plant diversity increased with the increase of annual precipitation,and the construction of protected areas promoted the protection of diversity to a certain extent.The relationship between plant diversity and precipitation in Sanya City showed that the level of plant diversity was different in different regions and different vegetation types,the results of positive correlation between plant diversity and annual precipitation further confirmed that there was a certain similarity in the response of plant diversity to precipitation in coastal hilly areas,that was,there was a positive correlation between plant diversity and annual precipitation.(3)The comparative study on the stability of plant communities in coastal hills:A comparative study on the stability of plant communities in the same area and at different times(taking Tongguling plant community in Wenchang City as an example)showed that:the VR value of plant communities was 1.386 and the intersection point of the community stability was(31.055,68.945)in 2011,the VR value of plant communities was 1.935 and the intersection point of the community stability was(30.823,69.177)in 2018,so the VR value of the community in 2011 and 2018 were far away from 1,and the VR value of 2018 was larger,and the coordinate of the stable intersection point was closer to the equilibrium point(20,80),that was,the community develops in a more stable direction with the passage of time.A comparative study on the stability of plant communities in the different areas at the same time showed that:the VR value of plant communities was 2.251 and the intersection point of the community stability was(32.408,67.592)in Qionghai City,the VR value of plant communities was 2.292 and the intersection point of the community stability was(32.622,67.378)in Wanning City,the VR value of plant communities was 1.490 and the intersection point of the community stability was(32.914,67.086)in Lingshui County,the VR value of plant communities was 1.364,and the intersection point of the community stability was(33.034,66.966)in Sanya City,that meant,the community stability was different in different regions,and the stability decreased gradually from north to south along the latitude gradient.(4)A comparative study on the interspecific relationship of plant communities in coastal hills:The results of X² test,Pearson correlation coefficient test and Spearman's rank correlation coefficient test of interspecific relationship among plant communities in the same area at different times were consistent,which indicated that although most species in Tongguling plant community of Wenchang City in 2011 or 2018 had loose interspecific relationship,the interspecific relationship developed in the direction of stronger positive association,weaker negative association and increased positive-negative correlation ratio from 2011 to 2018,and this trend was consistent with the results of community stability.That meant a stable environment and less human disturbance were conducive to maintaining and promoting the stable development of the community structure,at the same time,the interspecific relationship of the plant community with stable structure would tend to be positive connection with the passage of time,and would develop in a more favorable direction of the community.The results of X² test,Pearson correlation coefficient and Spearman's rank correlation coefficient test for the comparison of interspecific relationships among plant communities in the different areas at same time were also consistent,indicating that although the interspecific relationships of most plants in different regions were loose,the negative association gradually increased,and the positive-negative correlation ratio decreased gradually from north to south along the latitude gradient.And this change trend was consistent with the results of community stability,that meant the positive correlation among plant communities with high stability was closer,and the reasons for the differences in interspecific relationship included not only the biological characteristics of plants themselves,but also environmental factors and so on.