Community Succession And Heavy Metal Variation In Robinia Pseudoacacia Tree Rings On Abandoned Escarpment

In this paper, escarpment sites abandoned in different years were taken as the researchareas. Typical samples were selected in each site type and the succession series were identified.In addition, Robinia pseudoacacia tree rings were taken as records for heavy matals variation indifferent succession stages. The comunity characters and heavy matal variation were sumerizedfor each succession stage. This study has great significance on the ecology restoration and itseffect estimate. The main conclusions are as follows:1. The succession series were identified4stages: junior succession stage(4a～7a), juniorsuccession and substitution stage(7a～18a), substitution stage (18a～44a)and approximateclimax stage(44a～75a). The succession series in detail are as follows: Lespedeza bicolor,Boehmeria nivea+Arthraxon hispidus, Artemisia argyiâ†'Broussonetia papyrifera, Ulmuspumila+B. nivea, Spiraea salicifolia+A. hispidus, A. argyi, Youngia japonicaâ†'Ailantusaltissima, Robinia pseudoacacia+B. papyrifera, S. salicifolia+A. argyi, Semiaqulegiaadoxoidesâ†'A. altissima, R. pseudoacacia, Pistacia chinensis+Flueggea suffruticosa, B.papyrifera, Ziziphus jujuba+S. adoxoides, Euphorbia pekinensis.2. In the growing structure, with the increase of years, percentage of herb andannual&biennial plants decreased, while percentage of arbor and shrub species increasedgradually. The numbers of family, genus and species show a trend from increase to decrease.Dominance index decreased, while diversity and evenness index increased. The communitiesbecome more and more stable, and the compositions of community species have zonalcharacteristics.3. With the increase of years,the temperate proportion is more and more in the flora ofabandoned quarries. In the quarry abandoned for75years, the temperate is the majordistribution type of the flora and the tropic counts for certain proportion,which indicates theflora in this stage has transitional charaeteristics from tropic to temperate.4. Heavy metal variation in different stages of community succession are as follows: Injunior succession stage, immature soil cann't make heavy metals change into the forms avaiablefor plants. In junior substitution stage, some kinds of heavy metals began to be changed intoforms avaiable for plants, such as Cu, Pb, Zn, Ni, and Cr. In senior substitution stage, heavymetal environment were further improved. In stable succession stage, most heavy metals wentback to normal level. Difference in type and content of heavy metals and complexity in theirtransfermation progress lead to different time they go back to normal level. Most of them havereturned to normal since the escarpment abandoned for about50years.