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Quantitative Studies Of The Effects Of Trampling On Typical Steppe Of Huanxian In Eastern Gansu, China

Posted on:2008-02-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:H L LinFull Text:PDF
GTID:1103360215457977Subject:Grassland
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An animal exerts three main influences on pasture - it treads, removes leaves (defoliates), and excretes upon it. Continued overgrazing and erosion cause range degradation by excessive animal trampling. Published studies that have examined the effects of grazing often do not distinguish between effects arising from these separate activities. Little is known about the result of trampling-induced feedback among the soil environment, grass and their interdependency. In addition, more information is needed on the effects of animal trampling on the managed grazing ecosystems. In typical steppe of loess plateau regions, where the management objective is maintaining grassland ecosystem structure and function, the impacts of grazing trampling can be a serious problem. This was one of the reasons for conducting this study on trampling effects. The object of the study was to evaluate separately the effect of trampling in typical steppe of Huanxian County in eastern Gansu Province, China. A series of field experiments were conducted there, which lasted for two years. They were involved of trampling intensity observation of tailing up Tan-sheep rotational grazing trail in summer season, trampling homogeneity trial, double factors trail between simulated precipitation and experimental trampling. Firstly, the index of trampling intensity and the strict trial method of experimental trampling were set up. Techniques of Mathematical Ecology were used to describe the variation among the response variables for the use levels (trampling intensity and simulated precipitation). This paper quantifies the impact of controlled experimental trampling on belowground plant biomass, soil physical and chemical properties and soil erosion under different precipitation conditions with tramping intensity as its core. The results were as follows.1. The trampling intensity (TI) proposed in the paper is defined under free or rotational grazing, trampling area or trampling pressure of grazing single or multiple livestock per hectare during a unit time. It has three expressive methods: trampling pressure method, trampling area method, trampling frequency method. The trampling unit and Trampling Equivalent Unit (TEU) were put forward for the first time in order to define the calculating standard and converting standard of TI.2. By tailing up and observing the flocks on typical steppe of Huanxian County in Eastern Gansu, China, a relation equation by regression analysis showed that livestock trampling intensity is increased by the power function of grazing intensity. This fully demonstrated that adjusting and controlling the trampling effects of grazing livestock is an important indication of grazing management. The trampling effects of grazing livestock played a key role in preventing the degeneration and maintaining the wholesomeness of the grassland.3. Manufacture of trampler was imitated for mechanic characteristics of Tan-sheep trampling. By a simulation homogeneity experiment, we compared experimental trampling and traditional Tan-sheep rotational grazing in summer season. Statistical analyses (t test) indicated that there were no significant differences between modelling Tan-sheep trampling and traditional rotational grazing in the height of leaf layer, species number of plant, the water content of top layer (0-15cm), the soil porosity, bulk density and soil compaction. There is homogeneity between experimental trampling and traditional grazing in the effect of grassland trampled. This lay the foundation for future research in animal trampling effects for more effectively.4. Early research on grassland root systems focused on qualitative descriptions of root system structure. But the response effects of roots for different trampling intensity are not well-understood. Taking trampling intensity and rainfall as independent variables, the coupling model of underground plant biomass of 0-10cm layer was scanned optimization with underground plant biomass maximum as a target. The most suitable grazing intensity for the typical steppe of Huanxian County was decided to be 3.84-5.09 sheep unit/hm2 which is converted by the relation equation between trampling intensity and grazing intensity. The models offered a new pattern and quantitative tool for the grazing system management.5. There are 48 experimental treatment combinations on five soil chemical indicators in field controlling experiment of two factors: experimental trampling and simulated precipitation. The analysis results by multivariate and multiple analyses of variance indicate that there is significant difference between hydro N (mg/kg) and total P (%) in trampling intensity gradient. However, there are significant differences among hydro N (mg/kg), total P (%), available P (mg/kg) and the content of soil organic matter (%) in simulated precipitation gradient. This shows that soil chemical properties are more sensitive to simulated precipitation. The effects of interaction between experimental trampling and simulated precipitation have significant influences on hydro N (mg/kg), total P (%) and organic content. Trampling and simulated precipitation factors play a role in facilitating ecosystem state change in the typical steppe of Huanxian County in Eastern Gansu, China.6. We analyzed the soil mechanical composition (0-15cm) of different trial sample plots in field controlling experiment of two factors: experimental trampling and simulated precipitation. Fractal dimension can be calculated by using fractal model. The result shows that fractal dimension characterized by heavy trampling plot-4 W -1.3333×10-4 T. The soil eroding process also can be characterized fractal dimension values decrease. So, in this sense, fractal dimension measurement has certain indication significance with evaluation of soil erosion. This pushes forward future research in soil erosion mechanism in grazing grassland.7. The sensitivity of soil erosion to trampling-caused was changed with various different combinations of experimental trampling and simulated precipitation. Compared with traditional regression model, the artificial neural network model by Error Back Propagation (BP) can complete the news treatment of the whole network by means of a mutual function between the neural units, and has a lot of merits of self-learning, self-adjusting and fault tolerance such like. Therefore it is feasible that the soil erodibility factor K value is calculated by the neural network. Soil erodibility is complicated, which is affected by many factors such as trampling and precipitation. The artificial neural network model skipped the mechanism of soil erodibility, conducted research on soil erodibility by both trampling and rainfall factors. Obviously, this was an innovative attempt to precisely evaluate soil erodibility for understanding soil erosion regularity.8. Trampling directly facilitates erosion by hoof. Trampling of the soil is the most important factor contributing to erosion. Study results indicated that in grass growth period, moderate and heavy trampling aggravated soil erosion risk under arid circumstances. Precipitation has the effects of two-side regulating soil erosion. With increasing trampling intensities, precipitation can lower soil erosion modulus, but soil erosion modulus will increase with decreasing trampling intensities. However, the restriction effects of simulated precipitation on soil erosion were less than the trampling effects on soil erosion. The mechanism model, which took soil erosion modulus as dependent variable and takes experimental trampling and simulated precipitation as independent variable, was validated by experimental data. This can provide a new method for the evaluation of soil erosion in arid and semi-arid grassland regions. With soil erosion minimum as a target, the most suitable grazing intensity can be obtained by analyzing precipitation amount in different forage growth period. Obviously, this is an innovative attempt for ascertaining grazing capacity rationally. 9. The ecological restoration of degraded grassland ecosystems has become the key task for the future sustainable development. So an integrated method for calculating a rational stocking density should be adopted. It gives attention to two things: underground plant biomass and soil erosion, besides the balance between forage yield and livestock utilization. The most suitable grazing intensity calculated by the integrated method can be denoted as minimum ("determine livestock carrying capacity according to grass", the suitable grazing intensity with underground plant biomass maximum as a target, the suitable grazing intensity with soil erosion minimum as a target). As a result, the most suitable trampling intensity for the typical steppe grassland of Huanxian County is decided to be 39 UST /hm2, in which the precipitation amount in forage growth period is 224.9mm, and the corresponding most suitable grazing intensity converting by the relation equation between trampling intensity and grazing intensity is 3.8 sheep unit/hm2.
Keywords/Search Tags:trampling, trampling unit, trampling equivalent unit, trampling intensity, experimental trampling, model
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