Impacts Of Different Disturbances On The Vegetation Restoration Of Abandonded Farmland

In China,'Grian for green'program is a key government forest restoration program which aims to replant forest or grassland on agricultural lands with a slope of over 25 degrees. However, larger areas of abandonded farmland which failed to achieve vegetation restoration distributes extensively in the west of China, due to divers reasons. Because the ways of abandonded farmland managment and using are various, the plant communities succession in abandonded farmland which resulted from different anthropogenic disturbances are various as well. However, few studies focus on the impacts of different disturbances on vegetation succession in abandonded farmland. The changes of plant community in abandonded farmland are the key indicator for measuring and evaluating the forest restoration and ecological consequences of the'grain for green'program. Characteristics of plant community reflect the direction and the speed of vegetation restoration. Therefore, it is distinctly important for properly managing abandonded farmland and realizing the aim of vegetation restoration, to examine and analyze the situation of vegetation restoration after conversion of farmland under different disturbances in certain stage.We hypothesized that different disturbances could result in significant difference of vegetation restoration effects in abandonded farmland, while the difference can be indicated by quantitative assessment index on plant community structure, function and dynamic. Here we choosed abandonded farmland with same de-farming time, coincident soil condition, and close topography and geomorphology condition as study object in Weixi County, northwest of Yunnan Province, and divided abandonded farmland into 3 sample plot, grazing land, fenced land and protected land, according to the different disturbance types. Then we analyzed how the biodiversity, aboveground biomass, and growth of Pinus yunnanensis seedlings of plant community in abandonded farmland changed, which resulted from ecological restoration under different disturbances, and discussed influence of different disturbances on vegetation restoration succession in abandonded farmland. Conclusions were as follows:(1) Plant species composition, dominant species, life form structure, community structure and species diversity were all different in abandonded farmland under different disturbances. The sizes of Margalef richness index and Shannon-Wiener diversity index of plant species in abandonded farmland under grazing, being fenced and being protected disturbances in order were grazing land> fenced land> protected land. With the disturbance intensity increased, species richness and species diversity showed the trend of increase firstly, and then decreased, which supported the intermediate disturbance hypothesis (IDH). Protecting and fencing disturbance both would benefit abandonded farmland to keep high level of plant species biodiversity, especially fencing disturbance. On the contrary, grazing disturbance would result in plant species loss significantly, and would not benefit to keep plant species biodiversity.(2) The aboveground biomass sizes of plant community in abandonded farmland under 3 types of disturbances in order were protected land> fenced land> grazing land. The aboveground biomass in grazing land was lowest, while the aboveground biomass in protected land was higher than others significantly (P<0.05). In other words, protecting disturbance would benefit abandonded farmland to restore biomass. On the contrary, it was low of aboveground biomass of community in abandonded farmland under grazing and fencing disturbance, and would not benefit to restore biomass.(3) The growth quality of Pinus yunnanensis seedlings in abandonded farmland under different disturbances in order were protected land> fenced land> grazing land. The growth of Pinus yunnanensis seedlings both in protected land and fenced land were better than that in grazing land significantly. Grazing with high disturbance intensity could restrain the growth of Pinus yunnanensis seedlings in abandonded farmland, and prevent the community from developing to the direction of progressive vegetation succession.(4) Protecting and fencing would positive affect the vegetation restoration in abandonded farmland, while over grazing precent vegetation from restoring, and even bring about vetetation degradation. For maintaining biodiversity and natural ecosystem operating normally in abandonded farmland, the influence of disturbance process must be considered in biodiversity protection, productivity maintainance and vegetation restoration, and choose more reasonable and effective ecological management measures.