| Soil moisture is a restrictive factor to the ecological construction on the Loess Plateau.Its dynamics is of great significance to the vegetation construction on the Loess Plateau under the background of climate change.However,the acquisition of soil moisture data needs a lot of manpower and material resources,and the existing soil moisture simulation models are various,and their applicability is still need to be explored.In order to solve the problem of soil moisture data acquisition in areas with limited or lack of soil moisture data,this paper used the soil moisture stochastic model which based on water balance and probability and statistics theory to simulate soil moisture.In the Ji County Forest Ecosystem Research Station,this study choose the typical forestlands in the loess region of Western Shanxi including artificial Pinus tabulaeformis forest,Robinia pseudoacacia forest,and Populus sylvestris×Quercus liaotungens'is secondary forest as research objects,soil moisture,rainfall,soil and biological data in 11 consecutive growth seasons in 2005-2015 were collected,forest hydrological process and soil moisture characteristics were analyzed.According to measured parameters,soil model parameters which include soil porosity,soil saturated hydraulic conductivity,absorption coefficient,wilting coefficient,water stress starting point,field capacity,soil evaporation,root depth,canopy layer interception threshold,maximum daily evapotranspiration,precipitation amount and frequency were optimized by genetic algorithm method.This paper built soil moisture model,simulated soil moisture probability distribution,and evaluated the applicability of soil moisture model in typical forest ecosystems in loess region.Influence of the sampling interval on the model simulation results and parameter sensitivity to the model were analyzed.Soil moisture was simulated under different rainfall conditions.The main research results were as follows:Rainfall,total porosity and forestland evapotranspiration were the main factors influencing soil moisture.Therefore,they can be used as important parameters for the construction of soil moisture model.All the studied forestlands suffered from water deficit during 2005-2015.Vegetation growth was subjected to mild or moderate water stress.Although the soil moisture of the studied forestland was compensated by rainfall during rainy season,the compensation amount was far from enough.In drought years in the study area,the medium dry layer even appeared in Pinus tabulaeformis forestland and Robinia pseudoacacia forestland,and the appearance frequency of medium dry layer in Pinus tabulaeformis forestland was relatively high,which affected the plant growth.The study area satisfied all the assumptions of Laio soil moisture stochastic model,and the model could be used to simulate soil moisture dynamics in the study area.The simulation results showed that the model is effective for simulating soil moisture in root zone of Pinus tabulaeformis,Robinia pseudoacacia and secondary forestland.The model had a good applicability in typical forest ecosystems on the Loess Plateau.The data sampling interval had a little effect on the simulation results.The soil moisture data with long sampling interval can be used to calibrate the model.When calibrating the model,it was recommended to use soil moisture data with a sampling interval of no more than 10 days so as to reduce the loss of soil moisture fluctuation information.The model was strongly sensitive to variations of input parameters,including maximum evapotranspiration rate,average precipitation depth and average precipitation frequency,which should be paid more attention for stable and reliable simulation results.Based on the average precipitation amount and frequency in growth season,effective water storage of different forestlands during various precipitation type years were simulated,which could provide data support for the vegetation construction in the study area. |
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