From 2002 to 2003, based on the investigation of sample plots and stem analysis of remained plantation communities in the areas of returning farm to forest in 1980's in Datong county, Qinhai Province, this paper studies tree productivity and moisture potential productivity of six types of plantation on the land of returning farm to forest，such as Green Poplar (Populus cathayana Rehd.) and shrub mixed forest, Asia White Birch (Betula platyphylla Suk.) and China Spruce (Picea asperata Mast.) mixed forest, Dahurian Larch (Larix gmeini Rupr) pure forest, China Spruce pure forest and Asia White Birch pure forest and so on. The results show that: in sub-humid region of Loess Plateaus, 3000 per hmP 2 Pis a proper standard of planting density. At present lever of technique and economy, the productivity index of Green Poplar and shrub mixed forest, Asia White Birch pure forest, China Spruce pure forest and Asia White Birch and China Spruce mixed forest with the density of 2100-3333 per hmP 2 P can be served as potential productivity standard of actual biomass of arbor established forest under the condition of local normal planting techniques. In sub-humid area, it is adopted Thornthwaite Model to estimate plant climate potential productivity which is about 8462kg/(hmP 2 P﹒a) in this area. The actual potential water productive efficiency of Purplecone Spruce (Picea purpurea Mast.) and Asia White Birch pure established forest are 17.22 and 22.14kg/(mm﹒hmP 2 P﹒a) respectively, and that of Green Poplar and shrub mixed established forest and Asia White Birch and China Spruce mixed established forest are 21.14 and 19.09kg/(mm.hmP 2 P.a) respectively. The potential productivity of Green Poplar and shrub mixed forest, Asia White Birch and China Spruce mixed forest, China Spruce pure forest and Asia White Birch pure forest which have grown into forest with the density of 3000 per hmP 2 P have attained or closed to that of local climax community, which is local maximum tree productivity at present level of technique and economy. These types of forestation models are the developing direction of the returning farm to forest project.

2000年在山西方山，采用LI-6200光合测定系统和LI-1600稳态气孔仪，对不同集水措施试验地的刺槐、侧柏和苹果的生理指标进行了实地观测，并辅以相同树种实地盆栽苗木水分胁迫条件下的林木生理指标观测，研究了林木净光合速率、羧化效率、水分利用效率与土壤含水量的定量关系｡结果表明：维持刺槐､侧柏和苹果净光合作用的最佳土壤含水量分别为17.13%､15.9%和16.11%，三树种维持叶片水分利用效率的最佳土壤含水量依次为13.23%、10.66%和12.38%；羧化效率最高时的土壤含水量临界值依次为15.7%、15.5%和15.8%；土壤水合补偿点分别为4.55%、3.91%和4.49%｡上述三树种蒸腾速率所适宜的土壤含水量分别为18.82%、19.70%和16.33%｡根据集水造林的基本构思，可选取维持最佳叶片水分利用效率的土壤含水量临界值作为集水造林林木密度调控的土壤水分阈值和林木需水量的低限计算条件｡这一指标可量化为刺槐10%～13%，苹果10%～12.5%，侧柏9.5%～11%｡

应用森林水文学、土壤物理学和土壤水动力学的基本原理建立了林地土壤水分运动的数学模型，以模拟林地土壤剖面水分变化、林地土壤的入渗、径流和水分再分布过程。土壤水分特征参数的测定采用了双环入渗器配多层张力计的野外实地土壤水分在分布法。

为了给退耕还林工程建设的树种选择提供依据，2002～2003年，通过实地观测并应用Penman-Monteith方程和定位通量法，对青海大通黄土高寒区自上世纪80年代陆续退耕还林后营造的青海云杉（Picea crassifolia）、紫果云杉（Picea purpurea）、华北落叶松（Larix principis-rupprechtii）、白桦（Betula platyphylla）、青杨（Populus cathayana） 和沙棘（Hippophae rhamnoides）进行了林木耗水特性研究。结果表明：两种方法测算林地蒸散的月平均相对误差是5.7%。成龄林的青杨沙棘混交林、白桦纯林、青杨灌木混交林和白桦青海云杉沙棘混交林的生长季蒸散总量为488～538mm，其中蒸腾量占蒸散总量的74%～79%，林地土面蒸发总量占蒸散总量的10%～12%，林地无地表径流产生；处于中幼龄生长阶段的紫果云杉、青杨、华北落叶松、青海云杉混交林林分的平均蒸散总量为450～510mm，其中蒸腾总量占蒸散总量的45%～69%，林地土面蒸发总量占蒸散总量的16%～44%，地表径流量占林地降水量的1%～6%。大部分林分6～8月的蒸腾耗水量占全年的80%。

应用自记综合气象观测塔，对刺槐和油松林进行了以蒸散研究为目的的防护林热收支特性研究.结果表明：1994年生长季日平均实际太阳辐射量为7～24MJ·m-2；刺槐林林冠对太阳辐射的反射率为15%，油松林的反射率在10%以下，反射率的差异是造成两林分净辐射收支相差1～3MJ·m-2的主要原因.春夏两季林分获取的净辐射均由约70%～80%的太阳辐射转换而来；秋季的转换率约为60%，油松林的转换比刺槐约大1%～5%；防护林地区每天获取的净辐射量中，消耗于蒸散的潜热通量部分，在春夏秋三季分别为65%，82%和85%，油松林比刺槐林偏高1%左右；用于气温变化的显热通量部分在春季约占32%，夏秋为15%左右，其中刺槐林中显热通量部分在春夏两季所占的百分比相对油松要高出4%～5%；刺槐林地用于土壤热流量部分的热量在5～9月约占净辐射的1%～3%，油松林为2%～5%；1994年生长季刺槐林蒸散量为519mm，油松林为597mm。