Study On Vegetation Restoration After Conversion Of Farmland To Forests In Hutou Mountain In Dazhai

Dazhai village locates at the foot of Hutou Mt. southeast of Xiyang County town, Shanxi Province. The village situates in hinterland of Taihang Mountains with a mean elevation of 1000m.Due to the erosions by the floods for a long time, water and soil of Dazhai have lost seriously and restrict its development to great extent. In order to change the bad ecological environment, Dazhai Village has begun to plant grass and trees on the desert hills since 1950s, and taken converting farmland into forest as an important task for a long time, so the coverage rate of forest increases from 30% at the beginning to 43.3% in 1998.Based on the plant community samples of Hutou Mountain in Dazhai, we applied some quantitative ecological methods to analyze the relationship between plant community and environment.On the one hand, the types, structure and distribution patterns of plant community in the process of vegetation restoration are studied by TWINSPAN and DCA. On the other hand, plant diversity is studied at the different stage of succession by some biodiversity indices, and the change between community structure and soil component is also analyzed.The results are as follows:(1) Plant communities are classified into 20 types by TWINSPAN, and the figure reflects the changes of the succession time. Along the direction of matrix diagonal, the succession time gradually decreases from the upper left angle to the lower right angle, which is consistent with the survey results and the restoration time.(2) DCA ordination of the 48 samples mostly reflects the relationship between the plant structure and the succession time. From the left to the right in the DCA ordination, the succession time for plant community types increases gradually, from the upper part to the lower part, the altitudes of the restoration lands decreases gradually, which is consistent with the results of TWINSPAN.(3) Having selected shrub and herbage as the main study object, the process of plant restoration in Hutou Mountain can be divided into three stages. In the first stage, the farmland is converted into forest since 1990s and 2002, and there is mainly annual herbage, and the representative communities are Bidens parviflora+ Setria viridis, Bidens parviflora + Puccinellia distans. In the second stage, the time of converting farmland into forest is 1970s, and there is some vivacious herbage, and the representative communities are Cotinus coggygris var.Pubescens+ Vitex negundo var.heterophylla—Bothriochloa Ischaemum+ Carex lanceolata, Vitex negundo var.heterophylla+ Sophora viciifolia—Carex lanceolata+ Artemisia annua. In the third stage, the time of converting farmland into forest is 1966, and some regional plants begin to appear, and the main representative communities are Cotinus coggygris var.Pubescens+ Ostryopsis davidiana—Carex lanceolata+ Dendranthema chanetii, Myripnois dioica+ Vitex negundo var.heterophylla+ Spiraea pubescens—Dendranthema chanetii+ Carex lanceolata.(4) With the increase of the restoration time ,the pH, the contents of Zn and Cu of the soil increase firstly and decrease secondly as a whole. As for the pH, it is always in the neutral range (7.05—7.32) , the contents of K and Mn of the soil decrease firstly and increase secondly. There is no obvious trend about the content of P. However, the main trends of N,organic and Fe are increasing.In summary, these results have some instructive values for the vegetation restoration and ecological reconstruction of the farmland converting into forest.