The Plant Characteristics In Abandoned Lands And Changi Ng Trend Of Width Between Agro-forest Ecosystems Under Different Abandoned Years

The full start of implementation of the Grain for Green Project in2002is China’s most ambitious ecological restoration and reconstruction works. This project has some impacts on land use and covers, thereby causing some changes of landscapes and ecosystems, especially the spatial pattern of mountain agro-ecosystems and natural ecosystems. In this study, we select two sampling sites on northwest Yunnan Province, Weixi County, which have same soil and topograpHy conditions but under different abandoned years. On the basis of community methods, we investigate the spatial distribution pattern of species diversity and determine the position and width of ecotone between abandoned farmlands and Yunnan pine forest under different abandoned years. Then to explore plant community structures、growth forms、the relationship between species diversity and geographical sites and the change trend between different ecosystems.Results are as follows.(1) The three-year abandoned land mainy compose of herb community. Teraceae and Poaceae are two dominate families. Annual herb Artemisia carvifolia is constructive species. Perennial herb Arthraxon laceolatus, annual herb Bidens bipinnata and small shrubs Desmodium yunnanense are three dominant species. The nine-year abandoned land has clear layer pHenomenon-tree, shrub, grass layer. Asteraceae, Poaceae and Rosaceae are three dominate families. In grass layer, Perennial herb Arthraxon laceolatus, Heteropogon contortus and annual herb Hypericum japonicum are three dominate species. In shrub layer, Chamaenerion nepalensis and Rubus yunnanicus are two dominate species. In tree layer, Pinus yunnanensis is dominate species.(2) The species composition and community structure in nine-year abandoned land are more rich and complex than that in three-year abandoned land which coincidence with the general community succession law. In study area, the abandoned lands take just nine years to return to the complex structure of the community. It shows that in this area, natural recovery is an effective mode of vegetation recovery. (3) Both in three-year and nine-year abandoned lands, the trend of species richness and Shannon-wiener index shows that ecotone> Yunnan pine forest>abandoned land. The trend of Pielou index shows that Yunnan pine forest>ecotone>abandoned land. Ecotone has the maximum value of CD and Cody index, minimum value of CP index.(4) Along the abandoned land and Yunnan pine forest transect, the change trend of soil pH shows that ecotone>abandoned land>Yunnan pine forest, the change trend of organic matter shows that ecotone>Yunnan pine forest>abandoned land. The soil in two abandoned lands are acidic(5.39-6.57), and the value of pH and organic matter both show that three-year abandoned land is lower than that in nine-year abandoned land. This can prove that forest has a better ability in keeping soil nutrients, the Grain for Green Project has a significant role of improving soil quality.(5) The important value of species can explicitly determine the position and width of the ecotone, and when the size of MSWD is six, the value of SED can clearly shows the position and width of ecotone. The width of ecotone in three-year and nine-year sampling sites are27m and50m. The result has a good coincidence in determining the position and width of ecotone using soil pH and organic matter indicatiors. On nine-year sampling site, the position and width of ecotone are the same when using soil and species indicators. The width of ecotone between abandoned land and Yunnan pine forest is keeping changing. As the growth of abandoned year, the width is broadening, the type of plant community in abandoned land can eventually recover to Yunnan pine forest.