Species Diversity And Community Characteristics Of Secondary Vegetation In Haitan Island

For exploring the species-distance relationship and the species diversity and characteristics of secondary vegetation in the research area of Haitan Island.Three line transect methods(a total of 9 sample lines)and standard sample methods(a total of 29 samples)were selected for vegetation survey in two inland mountains(Ruiling Shan and Dongyu)and one seaside mountain(Baiquan Shan)in Haitan Island.Using methods of curve fitting,important value calculation,group average clustering,species diversity index calculation,canonical correlation analysis and redundancy analysis to explore the differences of vegetation survey by the line transect methods and the species composition,community types and the relationship between species diversity and environmental factors of secondary vegetation in the research area.so as to provide reference for research of line transect method?vegetation construction and ecological protection in Haitan Island.The main conclusions are as follows:1.The cubic function model(y=A+B*x+C*x~2+D*x~3),exponential function model(y=a-b*c~x),power function model(y=a*x~b)are used to fit the circular line-transect,cross-shaped line-transect,v-shaped line-transect.The results showed that there was a significant correlation between the line-transect distance and the species number(R~2>0.9,P<0.01).The circular line-transect can get the most species number and the distance correspondingly longest.2.A total of 284 species of vascular plants belonging to 236 genera and 90 families were found in research area of Haitan Island.There are 3dominant families:Compositae?Gramineae?Leguminosae,and it is notable in dominant families,but the the dominant phenomena of genera are not obvious,and most of them are minor genus.Acacia confusa?Casuarina equisetifolia are the dominant species in tree layer of forest community,and Dodonaea viscosa?Elaeagnus oldhami etc.are the dominant species in shrub community while some samples's dominant species is not so clearly classified.The dominant species composition of understory vegetation in forest community is affected by human disturbance and habitat heterogeneity.3.Group average clustering are use to divide the secondary vegetation in research area,it consists of 6 formation types and 9 association types.The main vegetation types included Form.Acacia confusa?Form.Casuarina equisetifoli.?Mixed shrub and Dodonaea viscosa shrub?Form.Acacia confusa+Casuarina equisetifolia?Elaeagnus oldhami shrub.The association types included Casuarina equisetifolia-Lantana camara+Agave americana-Bidenspilosa,Casuarinaequisetifolia-Sageretia thea-Oplismenus undulatifolius+Conyza bonariensi,Casuarina equisetifolia-Spinifex littoreus+Bidens pilosa,Acacia confusa-Dodonaea viscosa-Dianella ensifolia,Acacia confusa-Elaeagnus oldhami-Bidens pilosa,Acacia confusa-Sageretia thea-Praxelis clematidea,Acacia confusa+Casuarina equisetifolia-Casearia glomerata-Cyclosorus parasiticus,Dodonaea viscosa-Dianella ensifolia,Elaeagnus oldhami–Bidens pilosa,Mixed shrub?4.The life form spectrum and the leaf characteristics presented the feature of the high proportion of therophytes(21.81%~26.70%),nano-phanerophytes(36.72%~40.43%),non-sclerophyll(85.31%~89.53%),non-entire leaves(52.66%~58.64%),single leaves(82.20%~83.62%)and microphyll(61.26%~62.77%),which showed the adaptation of life form and leaf functional traits to the environment(strong breeze and poor soil)in research area.In addition,the high proportion of therophytes also is a indication of secondary properties of the vegetation in research area.5.The species diversity level of Acacia confusa forest was higher than that of Casuarina equisetifolia forest in the research area,and close to that of the same vegetation type in it's nearby latitude Subtropical islands.The species diversity level of mixed shrub vegetation is higher than that of Acacia confusa forest.The result of canonical correlation analysis(CCA)ordination showed that:Altitude(P<0.05),soil available potassium(P<0.05),soil total nitrogen(P<0.05),pH(P<0.05),slope aspect(P<0.05)were the main environmental factors affecting species composition and community distribution of secondary vegetation in the research area.The redundancy analysis(RDA)ordination showed that soil available potassium(P<0.05)and soil total nitrogen(P<0.05)were the main environmental factors affecting the species diversity index of secondary vegetation in the research area.Soil available potassium and soil total nitrogen were the main environmental factor affecting the secondary vegetation plant communities.The CCA and RDA's explanation variance was about 25%,there are still 75%of the factors that can not be interpreted,it may be attributed to some environmental factors which were not to be selected,such as human interference.