| A Comparative Study on Understorey Vegetation Diversityof Eucalyptus Plantation in Hainan IslandAbstractEucalyptus is generally planted in South China for the characteristic of fastgrowing, strong resistance to disadvantage and broad usage. However, land degradation of Eucalyptus Plantation ecosystem has become a teething problem for its?simple structure and poor biodiversity of understorey vegetation, which associated with the neglecting the influence of understorey vegetation. Understorey vegetation is an important component of Eucalyptus Plantation ecosystem. This paper intend to find the critical factors which influence diversity of understorey vegetation on the basis of comparative analysis of the flora component, species and plant diversity of understorey vegetation and study on the biomass of vegetation. This make a foundation for developing a appropriate growing understorey vegetation. Furthermore, it provide a theoretical basis for the sustainable management of Eucalyptus Plantation. The following give the main results of this research.There are 224 of wascular bundle plant altogether in the plots investgated which belong to 65 families and 153 genera separately. 88 species of wascular bundle plants which occupy 39.3% are woody plants. while 136 species of which occupy 60.7% are herbs. Shrub-vegetation and pure grass are the types of understorey vegetation structure.The species of Myrtaceae, Malvaceae and Euphorbiaceae are dominant shrubs,while the species of Compositae,Rubiaceae and Gram ineae are dominant herbs. Plots including the richest kinds of species can reach 37, while plots with the poorest can reach 4 of 153 plots investgated( 10 X 1 0m2).2.Diversity index of woody plants is the highest of understorey vegetation in Tunchang of the Island. The species richness S, Shannen-wiener index H?and Simpson index D is 25, 1.3567 and 0.9557 separately. These three indexes can reach 1, 0.0000 and 0.0000, lowest in coastal plafform. Three diversity indexes of herbs in mixed forest model Eucalyptus exserta Xpinus caribea are 18, 1.1538, 0.9201, which are the highest.Diversity index H~ and D of herbs are 0.2603 and 0.1896, the lowest values appearing in Eucalyptus Plantation of Datong,Tunchang, where Dicranopteris ampla dominates. Generally, for woody plants, the higher the S is, the bigger the corresponding H?and D are, but for herbs, things is just opposite ,especially forIIIEucalyptus forest in young period.3.Diversity index H?and D of woody plants have significant correlationship with soil moisture, annual rainfall, available N and P of soil, but none of these factors have significant correlationship with the H?and D of herbs. Annual rainfall is the first factor influencing on the diversity index of understorey shrub, soil moisture follows, and then available N.Species of woody plant and herb have the highest diversity index in the mixed model of Eucalyptus exserta XPinus caribea. But it can抰 be certain that understorey vegetation of mixed model must be the most appropriate type for maintaining the productivity of Eucalyptus Plantation and its sustainable management. Continuous planting and interplanting are two impediments to the increase of the diversity of herb and woody plant.Diversity of undershrub and herb plant have no significant correlationship with Eucalyptus stand age, that is to say, Eucalyptus stand age has no influence upon the growth and development of understorey vegetation.Comparison with several kinds of Eucalyptus stands, the highest diversity index H?and D of undershrub appear in 11-years Acacia stand, where index H and D are secondary to 9- years Eucalyptus I2ABL.4.For above-ground biomass of understorey vegetation in Eucalyptus plantation, the fact is that herb has more of it than woody plant does, especially in young stand. With the plantatio&s aging, difference of above ground biomass between herb and woody plant become small. There are dominant species in understorey vegetation of Eucalyptus plantation, the younger the plant...
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