环县典型草原放牧家畜践踏的模拟研究

Quantitative Studies of the Effects of Trampling on Typical Steppe of Huanxian in Eastern Gansu,China

Trampling is one of the three impact activities(trampling,defoliation,and excretion) performed by a grazing animal on grassland and also the major reason for range degradation.Little is known about the result of trampling-induced feedback among the soil environment,grass,and their interrelationship.In addition, more information is needed about the effects of animal trampling on the managed grazing ecosystems.In typical steppe of loess plateau regions,where the management objective is to maintain the grassland ecosystem structure and function,the impacts of grazing trampling could be a serious problem.The object of the study was to separately evaluate the effect of trampling on the typical steppe in Huanxian County,eastern Gansu Province,China.A series of field experiments were conducted for two years including the tailing-up observation of trampling intensity of Tan-sheep in summer rotational grazing trail,trampling homogeneity trial,two-factor trail of simulated precipitation and experimental trampling.The results are as follows.1.Trampling intensity(TI) was proposed by this paper as the trampling area or trampling pressure created by a single or multiple grazing livestock per hectare during a unit time under free or rotational grazing.It had three expression 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 calculation and conversion standard of TI.2.By tailing-up observation of the flocks on typical steppe of Huanxian County in Eastern Gansu Province,China,the regression analysis shows that livestock trampling intensity was increased by the power function of grazing intensity.This fully demonstrated that the trampling effects played a key role in the wholesomeness maintenance of grassland and the adjustment and control of the trampling effects of grazing livestock should be an important aspect of grazing management.3.Trampler was manufactured to imitate the mechanical characteristics of Tan-sheep trampling.By the simulation homogeneity experiment,we compared the experimental trampling area and traditional Tan-sheep rotational grazing area in summer season.Statistical analyses(t test) indicated that there were no significant differences between the simulated area created by the trampler and the traditional rotational grazing area in the height of leaf layer,vegetative species number,soil water content of top layer(0-15cm),soil porosity,bulk density,and soil compaction.This homogeneity provided the foundation for more accurate research in animal trampling effects out of defoliation and excretion in the future.4.Taking trampling intensity and rainfall as independent variables and maximum underground plant biomass as target,the coupling model was optimized for underground plant biomass in 0-10cm soil layer.The most suitable grazing intensity for the typical steppe in Huanxian County was decided to be 3.84-5.09 sheep unit/hm2 which was converted by the conversion equation between trampling intensity and grazing intensity.The models offered a new quantitative tool for the grazing system management.5.Five soil chemical indices were analyzed by multivariate variance in a two-factor(experimental trampling and simulated precipitation) controlled field experiment including 48 treatment combinations.The analysis results by multivariate and multiple analyses of variance indicate 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(0-15 cm) of different sampling plots in a two-factor(experimental trampling and simulated precipitation) controlled field experiment.Fractal dimension of soil particle were calculated using fractal model.The result shows that a negative correlation was found between fractal dimension and trampling intensity.However,the decreased extent of fractal dimension was related to the simulated precipitation level.When the precipitation level was dry,natural precipitation,moderate rainfall,and abundant rainfall,the declined extent of fractal dimension value was 4.33%,2.61%,1.34%,and 1.23%,respectively.The matching relationship between precipitation and trampling determined the fractal dimension values.Two-variable regression pattern was established as follows: F=2.427+2.0982×10-4W-1.3333×10-4T The soil eroding process can also be characterized by the decreased fractal dimension values.Therefore,soil fractal dimension measurement could be meaningful for the soil erosion evaluation.7.Compared with traditional regression models,the artificial neural network(ANN) model has better ability of imitation and prediction.Therefore the soil erodibility factor K value was calculated by ANN model based on the independent variables of the accumulated trampling effects per unit area and simulated precipitation.The ANN model allowed to skip the complicated soil erodibility mechanism and establish the relationship between the soil erodibility and its influencing factors,e.g.trampling and rainfall.Obviously,this was an innovative attempt to precisely evaluate the soil erodibility.8.Trampling by the hoof action of grazing animals is the most important factor contributing to soil erosion.Study results from the different combinations of experimental trampling and simulated precipitation indicate that the moderate and heavy trampling aggravated the risk of soil erosion under arid circumstances during the growth period of grasses.Precipitation had two-side effects on soil erosion.However,the restraint effects of simulated precipitation on soil erosion were less than the stimulative effects by trampling on soil erosion.The mechanism model,which took soil erosion modulus as dependent variable and the experimental trampling and simulated precipitation as independent variables,was validated by experimental data and could be used as an innovative method to evaluate the soil erosion in arid and semi-arid grassland regions.Taking minimum soil erosion as the target,the most suitable grazing intensity could be rationally ascertained by analyzing the precipitation amount during different forage growth periods.

Trampling is one of the three impact activities （trampling, defoliation, and excretion） performed by a grazing animal on grassland and also the major reason for range degradation. Little is known about the result of trampling-induced feedback among the soil environment, grass, and their interrelationship. In addition, more information is needed about the effects of animal trampling on the managed grazing ecosystems. In typical steppe of loess plateau regions, where the management objective is to maintain the grassland ecosystem structure and function, the impacts of grazing trampling could be a serious problem. The object of the study was to separately evaluate the effect of trampling on the typical steppe in Huanxian County, eastern Gansu Province, China. A series of field experiments were conducted for two years including the tailing-up observation of trampling intensity of Tan-sheep in summer rotational grazing trail, trampling homogeneity trial, two-factor trail of simulated precipitation and experimental trampling. The results are as follows.