Soil Condition Of Herb And Shrub Stage Of Vegetation Secondary Succession In The Hilly-Gullied Loess Region

Vegetation restoration is the key task of ecological construction in the loess plateau of China. There has been many research and publications about the impact of vegetation restoration on soil quality in this region. However, quite fresh research was done on how soil quality affects on vegetation restoration. In this thesis, taking the soil-vegetation system as the research object, using an approach of spatial sequence instead of temporal sequence, through sampling in the root zone of selected typical vegetation communities in herb and early shrub succession stages, combining with field investigations and laboratory test, we studied soil physical properties, nutrients and trace elements in the soil profile of the five kinds of herbal community and seven kinds of shrub trees. Based on this, suitable soil condition and the key soil factors for the secondary succession from herb to shrub were identified. The research was meaningful for understanding the interactive effects of soil and vegetation, and the results could be a reference for artificial controlling of speed up the process of vegetation restoration succession. Main conclusions are as follows:1. The characteristics of vegetation community restoration in the different types of landforms were clarified in the hilly-gully loess region of China. The corridor function of vegetation fence along the edge of the gully and the patch distribution of vegetation in the gully were demonstrated. With hill closing measurement carried out about 20 years, vegetation succession has expressed a healthy proceeding succession trend with a great abundances and diversity. At present in the side of life forms of plant communities, herbage plants were the major, especially perennial herbage, while shrub and arbor trees also have importance position. Shrub and arbor trees have importance influenced on the diversity and structure of plant communities and so on. Patch pattern of vegetation distribution was prominence in the gullies. Differences were found between the construction pattern of importance values of shrub and arbor trees in different direction gullies. We also found that the South-north gully was more uniform than the west-east gully. There were some differences in the similarity of vegetation species in different gully direction; however, these differences were mainly affected by some coexistence species and ancient species.2. The characteristics of soil physical properties of herb and early shrub stage in vegetation secondary succession were clarified. In the herb stage of vegetation secondary succession, the soil physical properties have been improved, and improvement effect of the physical properties of the soil surface was better than the other soil layers. But there was no linear relationship between the changes of soil physical property and succession time. With the herb community succession, the trend of different soil physical changes. Soil physical properties of natural grassland were better than artificial grassland. With the exception of soil moisture, soil bulk density, porosity, stability, infiltration and water stable aggregates of shrub were better than Bothriochloa ischaemum. It showed that improvement of soil physical properties by herb communities succession provided a basic soil physical conditions for shrub trees ecesis and development. Different shrub trees needed different proper soil physical condition of ecesis.3. The characteristics of the soil nutrient of herb and shrub stage in vegetation secondary succession were clarified. With the herb community succession, soil nutrients showed an improving tendency in general. Different soil nutrient factors in the profile varied differently. It seems that soil nutrient status was controlled by the dominant species of the community rather than successional time. Soil nutrient status of early shrub was better than herb stage. It demonstrated that it needs more restricted nutrient condition in early shrub stage than herb stage. Different shrub trees had different condition on selection and adaptability of ecesis.4.The characteristics of the soil available trace elements of herb and shrub stage in vegetation secondary succession were understood. In the herb stage, contents of different kinds of soil available race elements were different. It showed that Mn> Fe> Cu> Zn. Between 0~10cm and 10~20cm soil layers, changes of contents of Zn and Mn were significantly different, however, no significant difference was found in the contents of Cu and Fe. With the herb community succession, available Zn and Mn contents showed an increasing trend, available Cu content had a waving change, available Fe content appeared the trend from increasing to decreasing. In the early shrub stage, contents of different kinds of soil available race elements were different. It showed that was Mn> Cu> Fe> Zn. Changes trend of different kinds of soil available race elements in the profile were different. Between 0~10cm and 10~20cm soil layers, the change of available Fe content was significant, the change of available Cu, Mn and Fe content were not significant. Different shrub trees were difference in the need and adaptability of the soil available trace elements contents. In the early shrub stage, there was a significant linear relationship between soil available trace elements and soil nutrient, as well as soil pH, but except available Cu. 5. Suitable soil condition and the key soil factors for the secondary succession from herb to shrub were identified. In the early shrub stage of vegetation secondary succession, minimum critical values of soil physicals (except soil moisture) and soil nutrient factors were higher than herb stage in general. The range of the soil nutrient contents (except total phosphorus) in the early shrub was bigger than herb stage. The minimum critical value of soil available Mn in the early shrub was higher than herb stage. The range of the soil pH and the soil available trace elements were in general bigger than herb stage. The three factors of soil nutrient accumulations, environment of soil material exchange and soil permeability, which were identified using principal analysis, could basically reflected soil condition information of the herb stage. Availability of nutrient elements, soil nutrient accumulations and soil perviousness could basically reflected soil condition information of the early shrub stage. Organic matter, pH and porosity had great influence on soil condition of the herb community stage and might be the key soil factors in the herb stage. Available Zn, soil P elements and bulk density had significant influence on soil condition of the early shrub stage, which might be the key soil factors in the early shrub stage.