Simulation of water productivity and soil desiccation of artificial Pinus tabulaeformis forestland on the Loess Plateau

صينى. 在EPIC模型模拟精度验证基础上，应用EPIC模型定量模拟研究了延安45年（1957～2001年）实时气象条件下，油松人工林地的水分生产力、10 m土层土壤有效含水量的变化动态和土壤湿度剖面分布特征，以揭示较长时段内油松人工林地的水分生产力变化规律和土壤干燥化效应。模拟结果表明：（1）1～13年生(1957～1969年)油松人工林水分生产力变化受降水量的影响不大，土壤水分足够维持油松较高的生产力，生物量平均值为3.1 t/hm2；14～45年生（1970～2001年）油松人工林水分生产力呈波动性下降趋势，其波动与降水量波动呈相同的趋势，生物量平均值为2 t/hm2。（2）延安油松人工林地0～10 m土层逐月土壤有效含水量模拟值，模拟前期（1～8年生）在较高（1 300～1 490 mm）水平上波动，模拟中前期(9～15年生)呈现明显的逐年降低趋势，土壤干燥化趋势十分强烈，模拟中后期（16～43年生）在较低水平上（0～180.0 mm）波动，模拟后期（44～45年生）油松死亡后土壤有效含水量逐年上升。（3）随着油松生长年限的延长和根系扎深，油松林地土壤的干层逐年加深和加厚；14年生以后，1～10 m深层土壤湿度稳定维持在每米土层0.12 m左右的含水量状态，表明油松人工林地1～10 m土层已经全部干燥化。综上所述，延安油松人工林地水分持续利用的最大年限为15年左右。

إنجليزي. Based on precision validation of the EPIC model, dynamic changes of water productivity of biomass, available soil water amount in 0-10 m soil layers and soil moisture distribution in soil profile of artificial Chinese pine tree（Pinus tabulaeformis Carr.）forestland in the north Shaanxi were simulated with EPIC model in 45 years period, to uncover the law for changes of water productivity and soil's desiccating efficiency. The results showed that: (1) Water productivity of 1 year-old to 13 year-old artificial forest was influenced slightly by the rainfall and the soil water content was enough for persistent high productivity, the average annual biomass was 3.1 t/hm2; and water productivity of 14 year-old to 45 year-old (1970-2001) artificial forests declined with fluctuation gradually, its trend was similar with rainfall, its average was 2 t/hm2, and it was zero in last several years. (2) Simulated available soil water amount in 0-10m soil layers fluctuated at high level (1 300-1 490 mm) with the change of the rainfall in 1-8 years growth period, and decreased significantly with strong soil desiccation during 9-15 years growth period, and it was at low level (0-180.0 mm) in 16-43 years growth period, and increased again in 40-45 years after the tree died. (3) Thickness and distributed depth of desiccated soil layers on artificial forests increased gradually as artificial forest aged and root distribution depth increased, and the 1-10 m soil layers water content maintained at the level of 0.12 m/m (less than 0.16 m/m), which indicated that the 1-10 m soil layers of the forestland was in a strong desiccated condition. To sam up, a reasonable growth age for soil water sustainable use of artificial forests in Yan'an was 15 years._