【作者】 叶兵；

【导师】 王彦辉；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2007， 博士

【摘要】 针对半干旱地区森林植被恢复、重建及经营管理中的森林植被耗水与林地水资源供需平衡的关键问题，于2003年雨季(7～10月)在官厅库区妫水河流域的北京延庆上辛庄小流域选定了小叶杨和刺槐2个当地主要造林树种的5个典型林分样地，利用热脉冲测定技术及水量平衡测定方法，在单株和林分尺度上研究了林木的蒸腾耗水规律、环境因子影响，以及典型林分的水量平衡组成。其结果可为该地区耐旱节水型树种选择及水源涵养林建设提供一定的科学依据，具有理论价值和实践意义。取得的主要结果如下：1)蒸腾耗水规律刺槐和小叶杨的树干边材液流速率均存在不同方位(东、西、南、北)的差异，但未发现这种差异与树冠结构和边材宽度存在相关；两树种树干不同位点的边材液流速率表现出由内向外增加的规律，深层位点的液流启动晚，关闭早；越靠近树皮，树干液流的活动时间越长。刺槐和小叶杨树干边材液流速率和液流通量均表现出明显的昼夜和季节变化规律：树干液流在夜间非常微弱，白天出现明显的单峰曲线；树干液流速率与太阳辐射强度、空气温度、空气湿度、土壤温度和风速之间均存在着显著相关。在7～9月份，树干液流保持较大峰值；而10月份则明显降低。刺槐的液流速率显著大于小叶杨，其生长季平均峰值分别为12.1cm／h和7.6cm／h；但由于刺槐边材面积小于小叶杨(边材率分别为14.8％和81.8％)，所以相同径阶刺槐单株的液流通量和日耗水量均低于小叶杨。不同径阶的小叶杨单株树干液流速率峰值存在显著差异，但规律性不明显；刺槐随径阶增大而树干液流速率有增高趋势，但并不明显。两个树种均可由胸径直接估算胸高处的边材宽度，从而估算出树干液流通量和日蒸腾耗水量；树干液流通量和日蒸腾耗水量表现出随树干胸径增大而增加的趋势。典型小叶杨林样地的日均蒸腾耗水量为1.37mm／d，刺槐林为1.46mm／d。2)水量平衡研究小叶杨和刺槐林的林冠截留和林地产流均受到降水特征和林分结构的显著影响。林冠截留量受降水量影响最大，其次为降雨强度；林冠截留率随郁闭度和叶面积指数增加而增大；林地产流量和降雨量及雨强存在显著正相关，但径流系数与降水特征相关性不显著：林地产流量和径流系数随地表盖度增加而减小，与土壤性质和地形(坡度和坡位)没有显著相关性。乔木蒸腾耗水是林分水量平衡的最大分项，小叶杨和刺槐林样地在7～10月份的林木蒸腾量分别为128.2～138.4 mm和92.1～187.0 mm；各样地林下植被蒸腾量远远小于乔木蒸腾量，各月均不超过10 mm：刺槐林林下植被蒸腾量大于小叶杨林；各样地7～10月份的土壤水分蒸发量均未超过50 mm，表现随郁闭度增加而减小的趋势。各林地土壤水分随土层深度变化而变化的趋势相同，0～20 cm土层变化幅度最大，为5％～28％，60 cm以下土层则多在7％～12％之间。各样地土壤含水量的时间排序为10月＞9月＞7月＞8月，不同林地的土壤含水量排序为缓坡刺槐林＞陡坡小叶杨林＞陡坡刺槐林＞缓坡小叶杨林＞台地刺槐林。2003年7～10月份的降雨量为231.8mm，少于当地多年同期平均值(约350mm)，属于偏旱年。7～10月间各样地的水量平衡计算表明，自然降雨不能充分满足树木生长需要，尤其是台地刺槐林(20年生)0～100cm土层的土壤水分亏缺达到138.2 mm；小叶杨林的水分亏缺值也较大，缓坡小叶杨林和陡坡小叶杨林样地分别为37.0 mm和53.5mm。从整体上看，小叶杨林水分亏缺大于刺槐林，因此不宜选择小叶杨在该地区山地造林。刺槐林在幼龄阶段蒸散量不大，但随着林龄增加，其耗水量可能会高于降水量而出现水分亏缺，因此需要采取减少耗水和维持林地水分平衡及产流能力的营林措施。更多还原

【Abstract】 Aiming at the water consumption of forest trees and the shortage of water resources during the construction of forests in semi-arid areas for water conservation,during the rain seasons in July to October of 2003,5 typical stand sample plots of 2 locally prior species, Populus simonii and Robinia pseudoacacia L., in the little watersheds of Shangxinzhuang Village,Yanqing of Beijing which is located in the Guihe Basin of Gaungting Reservoir,were selected.Heat pulse measurement technology and water balance method were used for the research on the rules of plant transpiration and water consumption, the impacts of environmental factors and the composition of water-balance typical stands at whole-tree and stand scales.The research findings may provide certain scientific justification for the selection of drought-resistant and water-conserving tree species for the area and the rational planning of constructing forests for water conservation.The major findings obtained are as follows:(1)Characteristics of transpiration and water consumptionThe stem sap flow velocities of Populus simonii and Robinia pseudoacacia L.are differentiated in different directions (in the east,west,south or north),however,no interrelationship to tree crown structure and sapwood width has been found.The sap flow velocities in different relative points of stem section appear a rule of increase from inside to outside.The sap flows in deeper inside start later and stop earlier.The activating time of the stem sap flow is longer when it is closer to the bark.The stem sap flow velocities and sap flow of Populus sirnonii and Robinia pseudoacacia L.are changed obviously according to the change of day and night, and seasons.The stem sap flows weakly in the night and flows in a single-wave curve in daytime. Solar radiation intensity,air temperature,air humidity, soil temperature and wind speed are in remarkable correlation with the stem sap flow velocities.From July to September,2003,the stem sap flows in a relatively high peak value,but in an obviously lower one in October.The sap flow velocity of Robinia pseudoacacia L.is remarkably bigger than that of Populus simonii, their respective average peak values in the growth season are 12.1 cm/h and 7.6 cm/h.But due to the smaller area of sapwood of Robinia pseudoacacia L.than that of Populus sirnonii (the respective sapwood rate are 14.8％and 81.8％),the sap flow turnover and daily water consumption of a whole tree of Robinia pseudoacacia L are lower than Populus simonii,based on the same diameter class. The peak values of whole-tree stem sap flow velocities of Populus simonii at different diameter classes varies without a certain rule.Robinia pseudoacacia L.has a unobvious tendency to heighten as the increase of diameter class. The stem sap flow turnover and daily transpiration water consumption of the two species can be estimated from the sapwood width at breast height, which is directly estimated from the diameter at breast height.The sap flow turnover and daily transpiration water consumption are increased as the increase of the stem diameter at breast height. The depth of daily average transpiration water consumption of the typical Populus simonii plot is 1.37 mm/d and of the Robinia pseudoacacia L.plot is 1.46 mm/d.(2)Research on the water balanceThe canopy rainfall interception and forest runoff yield of both Populus sirnonii and Robinia pseudoacacia L.are significantly influenced by rainfall characteristics and stand structure.The canopy rainfall interception is prominently influenced by rainfall capacity and secondly by rainfall inttensity.The rate of canopy rainfall interception is increased as the increase of canopy density and leaf area index.The forest runoff yield has a positive relation with rainfall capacity and rainfall intensity,but it is not so obviously correlated between the runoff coefficient and rainfall characteristics.Meanwhile the forest water runoff and runoff coefficient are decreased as the reduction of ground coverage,but the impacts of soil properties and topography (gradient and slope position) are not obvious.The transpiration water consumption of arbor wood is the major content of forest stand water balance.The forest transpiration amounts of Populus sirnonii and Robinia pseudoacacia L.stands from July to October are respectively 128.2～138.4 mm and 92.1～187.0 mm.The transpiration amount of vegetation under tree of stands is much lower than that of arbor wood transpiration,with an average amount of below 10 mm every month.However,the transpiration amount of vegetation under Robinia pseudoacacia L.is bigger than that of vegetation under Populus sirnonii.The water transpiration amounts of the soil in all stands in July to October have not exceeded 50 mm and they will decrease as the increase of the canopy density.The depth changes of soil moisture in all stands are similar,with the largest variation of 5％～28％in the soil layer of 0～20 cm and the common variation of 7％～12％in the soil layer under 60 cm.The time order of the amount of soil water content in all stands is October >September >July >August.The order of the amount of soil water content of different forestland is Robinia pseudoacacia L.on slow slope > Populus simonii on steep slope > Robinia pseudoacacia L.on steep slope > Populus simonii on slow slope > Robinia pseudoacacia L.on mesa.The rainfall capacity of July to October of 2003 is 231.8 ram,lower than the average (about 350 mm) of multiple years in the same place.Thus 2003 can be counted as a light dry year.The accounting on the water balance of all stands in July to October shows the natural rainfall cannot meet the demand of tree growth.In particular,the shortage of soil moisture in the soil layer of 0-100 cm for Robinia pseudoacacia L.on mesa reached 138.2 mm.Populus simonii is also faced with a serious moisture shortage.The moisture shortage for Populus simonii on slow slope and Populus simonii on steep slope stands are respectively 37 mm and 53.5 ram.Generally, the moisture shortage of Populus simonii is bigger than that of Robinia pseudoacacia L.Therefore,Populus simonii is not an ideal selection for the afforestation in mountainous areas of the locality.Although the transpiration of Robinia pseudoacacia L.is small at its youth, its water consumption will increase to even more than the rainfall capacity as its growth and thus cause to the shortage of water. As a result,water-conserving management measures should be adopted to maintain the forestland water balance and the forest water runoff yield.更多还原