黄土高原不同密度刺槐(Robinia pseudoacia)林地水分生产力与土壤干燥化效应模拟

Simulation of water productivity and soil desiccation effects of different planting density black locust forestlands on the Loess Plateau

应用WinEPIC模型模拟研究了1957～2001年期间黄土高原半湿润区长武和半干旱区延安不同密度刺槐（Robinia pseudoacia）林地水分生产力演变规律和深层土壤干燥化效应。结果：（1）长武和延安高密度（6000株/hm2）、中高密度（4500株/hm2）、中低密度（3000株/hm2）和低密度（1500株/hm2）等4种处理刺槐林地逐年生物量模拟值均呈现快速增加、达到最大值后又逐年波动性降低的变化趋势,林地密度越高早期逐年生物量越高,后期逐年生物量差异缩小,两地均以低密度处理逐年生物量平均值和累积生物量模拟值最高;（2）4种密度处理45年生刺槐林地年均耗水量值基本相等,长武和延安分别为603mm和566mm,但生长前期年耗水量明显高于后期,并高于同期年降水量,林地密度越高前期耗水量越高,中期以后各密度处理耗水量基本接近且波动趋势基本一致,林地密度越高干旱胁迫程度越重;（3）模拟生长初期,4种密度处理刺槐林地0～10m土层逐月土壤有效含水量均呈现强烈的波动性降低趋势,长武各密度处理刺槐林地分别在7～23年生、延安分别在7～17年生之后逐月土壤有效含水量均在0～200mm较低水平上随降水量变化而波动;（4）4种密度处理林地0～10m土层土壤湿度剖面分布年度变化剧烈,土壤湿度逐年降低且土壤干层逐年加厚,密度越高土壤干层加厚速度越快,长武在26年生、延安在17年生时低密度处理刺槐林地土壤干层厚度均已超过10m,此后2～10m土层土壤湿度保持相对稳定的干燥化状态;（5）长武和延安刺槐林地适宜种植密度分别以1500～3000株/hm2和1500株/hm2为宜,刺槐林地土壤水分可持续利用最大年限分别为26a和18a。

Water productivity changes and deep soil desiccation effects of different planting density black locust（Robinia pseudoacia）forestlands were simulated with WinEPIC model during 1957-2001 at Changwu on semi-humid areas and Yanan on semi-arid areas of the loess plateau.The simulated results showed that：（1）simulated annual biomass amounts increased rapidly in early growth stage,and then declined obviously with fluctuation when reached its maximum on high planting density（6000 plants/hm2）,high medium planting density（4500 plants/hm2）,low medium planting density（3000 plants/hm2）and low planting density（1500 plants/hm2）treatment black locust forestlands at Changwu and Yanan.The higher planting density of the forestland had,the higher annual biomass amount could obtain in early growth stage,and differences of annual biomass amounts between four treatments decreased in late growth stage.The highest average annual biomass amount and accumulated biomass amount in four treatments at Changwu and Yanan was low planting density treatment at both locations during 45 years simulation period.（2）Averages of simulated annual water consumption were almost equal on four treatments black locust forestlands at Changwu and Yanan,and its value was 603mm and 566mm separately.Annual water consumptions in early growth stage were obviously much higher than later stage,and it were higher than annual rainfall of the corresponding period.The higher planting density of forestland had,the higher water consumption could have,and water consumption amounts were close to each other and fluctuated simultaneously on four treatment forestlands after middle growth stage on both locations.The higher planting density of forestland had,the severer water stress could have.（3）Simulated monthly available soil water amounts in 0-10m soil profile of four treatment forestlands decreased rapidly with strong fluctuation during early growth stage.Monthly available water amounts on four treatment forestlands fluctuated with annual and seasonal rainfall changes in range of 0-200 mm after 7-23 years growth at Changwu and after 7-17 years growth at Yanan,（4）Annual soil moisture distribution declined acutely,and thickness of desiccated soil layer increased annually in 0-10m soil profile on four treatments forestlands at Changwu and Yanan.The higher planting density of forestland had,the faster increase rate of desiccated soil layer thickness could have.Thickness of desiccated soil layer on low planting density forestland was already over 10m when 26 year old at Changwu and 17 year old at Yanan,and soil moistures in 2-10m soil layers after that year remained steady desiccated status on four treatment forestlands.（5）Reasonable planting density of black locust forestland was 1500-3000 plants/hm2 at Changwu and 1500 plants/hm2 at Yanan separately,and maximum year for soil water sustainable use was 26 years at Changwu and 17 years at Yanan