| Soil desiccation, which showed as continuous severe soil water deficit, is an increasing serious limiting factor of artificial shrub forest growth on semi-humid, semi-arid and semi-arid drought prone areas of loess plateau. Based on soil moisture observation in deep soil layers of the artificial shrublands, the WinEPIC 3060 model, which was developed by USA and is a soil and water resources management and plant productivity simulation model, was used to simulate water productivity and soil desiccation effects in 0-10m soil profile on Caragana shrublands and Seabuckthorn shrublands on semi-arid, semi-arid drought prone region of the loess plateau during 1971 to 2000. The stability of artificial shrubland growth was analyzed, which provide the basic scientific foundations for withdrawing cropland to forestland and vegetation reconstruction on the loess plateau. The progresses of this study are as following:(1) Average soil moisture of 0-10m soil layers on 11 shrublands was9.11% on semi-humid, semi-arid and semi-arid drought prone areas of loess plateau. Except 4 years old Seabuckthorn shrubland located on highland, soil desiccation have already occurred on all 10 shrublands. Average soil water overuse amount was 485.0mm and average soil desiccation speed was 47.7 mm per year. Except short growth age shrublands,soil moisture in deep soil layers below 3m was obviously lower than grassland and soil stable moisture on various shrublands. Maximum water consumption depth was close or over 10m.(2) Databases of daily weather variable sequence, physical and chemical properties of soil profile, crop growth parameters of WinEPIC model at Yan'an, Guyuan and Haiyuan were established. Correlation coefficient of simulated and observed annual biomass and available soil water amount in root zone layers on Caragana shrubland were 0.678 and 0.675 respectively with 1% significant difference. This indicated that WinEPIC could be used to simulate water productivity and soil water use on artificial shrublands of loess plateau.(3) During 1971-2000 simulation period, the average of simulated annual biomass of Caragana shrubland at Yan'an, Guyuan and Haiyuan were 0.47 t/hm~2, 0.42 t/hm~2 and 0.24 t/hm~2 respectively, and simulated annual biomass decreased obviously and gradually with fluctuation after 9-14 years old; the average of simulated annual biomass of Seabuckthorn shrubland at Yan'an, Guyuan and Haiyuan were 1.30 t/hm2, 1.07 t/hm2 and 0.89 t/hm2 respectively, and simulated annual biomass decreased obviously with fluctuation after 8 years old. Water stress days on Caragana shrubland and Seabuckthorn shrubland increased annually with fluctuation after 10-12 years and 6-7 years growth separately.(4) During 1971-2000 simulation period, monthly available soil water amount in 0-10m soil layers on Caragana shrubland at three locations decreased slowly from 1 to 8 years old, and decreased violently during 9-13 years growth age, and changed sustainable and fluctuated with rainfall at low level after 14 years old. Soil moisture in 0-10m soil profile on Caragana shrubland at three locations deceased gradually with growth age increasing during 1-13 years old, and desiccated soil layers occurred and its thickness increased annually, it was over 10m when growth age was 13-14 years old. Soil moisture in 2-10m soil layers kept stable desiccated conditions after 14 years growth.(5) During 1971-2000 simulation period, monthly available soil water amount in 0-10m soil layers on Seabuckthorn shrubland at three locations decreased slowly from 1 to 4 years old, and decreased violently during 5-13 years growth age, and changed sustainable and fluctuated with rainfall at low level after 14 years old. Soil moisture in 0-10m soil profile on Seabuckthorn shrubland at three locations deceased gradually with growth age increasing during 1-13 years old, and desiccated soil layers occurred gradually and its thickness increased annually, it was over 10m when growth age was 13-14 years old. Soil moisture in 2-10m soil layers kept stable desiccated conditions after 14 years growth.(6) Soil water sustainable use age of Caragana shrublands and Seabuckthorn shrublands at Yan'an, Guyuan and Haiyuan were about 14-15 years and 13-14 years respectively.
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