【作者】 吕瑜良；

【导师】 刘世荣；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2007， 博士

【摘要】 传统上，多采用造林或采伐面积比例来研究森林植被变化对其流域水文效应的影响，虽然植被的数量变化得以反映，但植被的质量及空间分布变化无法体现。叶面积指数(Leaf area index，LAI)既能反映植被的数量和质量特征，也能描述植被的空间分布以及动态变化，可以充分体现植被特征的变化。川西亚高山暗针叶林是长江上游重要的森林植被类型，在涵养水源、保持水土、维护生态平衡等方面起着巨大的作用。本文以川西亚高山暗针叶林的主要类型之一——岷江冷杉(Abies faxoniana)林为研究对象，采用试验观测与模型模拟相结合的方法，在小流域尺度和林分尺度上，首先，以LAI为主研究了植被结构及空间分布特征；然后，分别研究了植被对降水的截留、土壤水分的时空分布及变异性以及植被蒸发散的时空变化特征；之后，模拟了小流域湿润指数(Wetness index)的时空分布，分析了湿润指数与植被、地形、土壤和气候之间的关系；最后，基于上述研究，评价了川西亚高山暗针叶林的生态水文功能，探讨了植被变化对其生态水文功能的影响。目的是揭示川西亚高山暗针叶林与水的相互作用关系，阐明其对流域水资源的调控机理。研究结果表明：试验小流域的植被主要为岷江冷杉原始林(面积占88％)，其次为青海杜鹃(Rhododendron przewalskii)灌丛(面积占12％)。岷江冷杉林可分为4个林分类型，依次为藓类-箭竹-岷江冷杉林、草类-箭竹-岷江冷杉林、草类-杜鹃-岷江冷杉林和藓类-杜鹃-岷江冷杉林。在生长季节，岷江冷杉林的LAI平均值为5.44±0.83，不同林分之间差异极显著，顺序为：藓类-箭竹-岷江冷杉林＞草类-箭竹-岷江冷杉林＞草类-杜鹃-岷江冷杉林＞藓类-杜鹃-岷江冷杉林；LAI的时间动态变化为单峰曲线，峰值在8月中旬，为5.82±1.32；随着海拔升高，LAI先增加后减小，转折点约在3000m处；不同坡向之间LAI的差异显著，半阴坡LAI大于半阳坡；LAI的变异系数在林分尺度上为10.02～12.22％，在小流域尺度上为19.79～22.80％，在海拔梯度上为7.64～23.09％，在半阴坡上为16.58％，在半阳坡上为13.44％。试验区降水量充沛，雨日多，以小雨和中雨为主。岷江冷杉林冠层截留系数在33～72％之间，平均值为48％。在生长季节，冠层最大截留量平均值为1.74mm，不同林分之间差异明显，顺序为：藓类-箭竹-岷江冷杉林＞草类-箭竹-岷江冷杉林＞藓类-杜鹃-岷江冷杉林＞草类-杜鹃-岷江冷杉林；冠层截留量、冠层最大截留量、附加截留量分别约占同期降雨量的39％、25％和14％。模型对日降水截留量模拟效果不理想，对整个生长季节平均截留量模拟效果较好，相对误差的平均值分别为33～35％、9～14％。地被物层最大持水率、最大持水量平均值分别约为700％、10.5mm，不同林分之间差异明显。试验小流域土壤容重小，孔隙发达，持水能力强，水分入渗率高，平均值分别为0.96g／cm~3、65％(总孔隙)和11％(非毛管孔隙)、276.7mm(0～40cm土层最大持水量)和51.4mm(0～40cm土层非毛管持水量)、2.63 mm／min(稳渗率)，在不同群落类型之间差异较小，但在不同土层深度之间差异较大。研究期间，土壤容积含水量在0.59～0.66之间，不同群落类型之间差异明显，杜鹃冷杉林最高，箭竹冷杉林其次，杜鹃灌丛最低。土壤含水量在土壤表层最高，45cm土层深度最低；随着海拔升高呈增加趋势，但超过3700m则减小；在不同坡向之间，0～30cm土层半阴坡高于半阳坡，30cm以下则相反；在不同坡位之间，下坡最高，上坡最低，中坡居中。土壤水分变异系数在0.22～0.41之间，随着土壤含水量增加而增大，随着土层深度增加或海拔升高而减小，半阴坡高于半阳坡，下坡大于中坡和上坡。用Priestley-Taylor模型改进式与Rithchie(1972)方法计算出，2005年，试验流域实际蒸发散为350.8mm，其中生长季节占55％；不同群落类型之间差异明显，草类-箭竹-岷江冷杉林最大(422.0mm)，杜鹃灌丛最小(248.4mm)，其它介于中间，依次为藓类-杜鹃-岷江冷杉林(363.1mm)，草类-杜鹃-岷江冷杉林(355.6mm)和藓类-箭竹-岷江冷杉林(323.4mm)。年蒸发散约占年降水量的35％，生长季节较低，非生长季节较高，分别占同期降水量的25％、71％。影响该区蒸发散的主导因子是太阳总辐射。生长季节降雨天数多，雾同多，日照时数短，太阳总辐射量少，是该区蒸发散低的主要原因。湿润指数在试验流域沟底较高，坡面较低；中部较高，上部和下部降低；半阴坡较高，半阳坡较低。不同群落类型之间，杜鹃冷杉林最大，箭竹冷杉林居中，杜鹃灌丛最小。降水量越大，太阳辐射越小，湿润指数越大；土壤水分含量越高，扩散速率越小，湿润指数越大；蔽阴系数越小，植被越稀疏，湿润指数越大。川西亚高山暗针叶林生态系统截留降水的综合能力较强，为89.5mm。其中，土壤层约占86％，地被物层约占12％，林冠层仅占2％。不同林分类型之间，林冠层、地被物层的截留能力、土壤层的蓄水能力以及植被蒸发散均存在差异，综合能力也不相同，顺序为：藓类-箭竹-岷江冷杉林＞草类-箭竹-岷江冷杉林＞藓类-杜鹃-冷杉林＞草类-箭竹-岷江冷杉林。随着LAI、植被盖度增加，最大冠层截留量与蒸发散增加，土壤含水量减少。但当植被盖度超过70％、LAI超过4.8时，蒸发散的变化不再明显。更多还原

【Abstract】 The proportion of cutting/forestation area is ususally adopted to quantify vegetation changes instudies of eco-hydrological influences of forest ecosystems. This may rational to some extentin quantifying vegetation changes, the change of vegetation in quality and spatial patternhowever, can not be mirrored. Leaf area index (LAI) can not only describe quantitative andqualitative characteristics of vegetation, but also exhibits its efficacy mapping spatial pattern aswell as temporal dynamic of vegetation. Sub-alpine dark coniferous forest in western Sichuanprovince, which is one of major natural vegetation types in the upper reaches of Yangtse River,plays a crucial role in waterhead protection, soil and water conservation and ecologicalequilibrium maintaining. Several key issues were addressed in this paper based on fieldobservation and experiment at both catchment scale and at stand scale, firstly, the quantitativeanalysis of vegetation structure and spatial pattern of Minjiang fir forest Minjiang fir (Abiesfaxoniana) stand, particularly the spatial and temporal pattern in terms of LAI; secondly,ecohydrological functions including canopy interception, soil moisture variability andevapotranspiration; thirdly, the spatio-temporal distribution of wetness index in the catchmentwas simulated by using TOPOG model, and the relationship between wetness index andvegetation, terrains, soil and climate; lastly, responses of these above-mentionedeco-hydrological functions to vegetation changes were therefore evaluated. The objective ofthis paper is to reveal the interactions between sub-alpine dark coniferous forest and water andilluminate the mechanism in regulating stream flows. The results showed as follows:The dominant vegetation in the catchment is Minjiang fir natural forest (occupies 88% of thecatchment area) and the secondary species are mainly Rhododendron przewalskii shrubs,(occupies about 12% of the catchment area). Minjiang fir forest can be classified into thefollowing four stand types based on difference in their understories: moss-bamboo-fir,grass-bamboo-fir, moss-rhododendron-fir and grass-rhododendron-fir. Single peak curve ofLAI seasonal change pattern occurred in sub-alpine dark coniferous forest during growingseason, with the peak value of 5.82±1.32 in the mid-August. Four stands showed significantdifferences in their LAI values (p＜0.001), with the mean LAI value of 5.44±0.83. The highestLAI occurred in the moss-bamboo-fir, followed by the grass-bamboo-fir and thegrass-rhododendron-fir, the lowest LAI value was in the moss-rhododendron-fir. Withincreasing altitude, LAI increased slightly at the beginning and followed by a dramaticallydecrease with the increasing elevation when exceeded 3000 m. LAIs at northeast-aspect standswas larger than those at southwest-aspect, the difference of LAIs between the two aspectswere signifcant (p＜0.05). The coefficient of variability (CV) of LAI at whole catchment scale is varies from 19.79% to 22.80%, this value was approximate twice in amount compared withstand scale (10.02～12.22%). CV varied with altitudinal gradients, the highest CV (23.09%)was occured at the elevation of 3800 m, while the lowest (7.64%) was at 3500 m. The CV atnortheast-aspect (16.58%) was higher than that of southwest-aspect (13.44%).Furry and moderate rains are the majority in this area and with abundant rainy days. Monthlyinterception rate of bamboo-Minjiang fir old-growth ranged from 33% to 72%, with theaverage of 48%. In growing season, there was a linear or powerful or exponential relationshipbetween rainfall and interception volume and a negatively exponential relationship betweenrainfall and interception rate when the amount rainfall was less than 10mm. The meanmaximum canopy interception by the vegetation in the catchment of 1.44km~2 in area was1.74mm and the marked differences among the five communities occurred in the followingsequence: moss-bamboo-fir＞grass-bamboo-fir＞moss-rhododendron-fir＞grass-rhododendron-fir＞rhododendron shrub. The simulated value of canopy interception rate,maximum canopy interception rate and addition interception rate of the vegetation in thecatchment were 39.24%, 25.36% and 13.88%, respectively. Simulation of the canopyinterception model was poor at daily scale but it is better at the overall growing season scale.The mean relative error of daily canopy interception was 33～35% and that over the wholegrowing season was 9～14%. In addition, the litter and moss layer had a higher water holdingcapacity (WHC) due to moss plant and more litter accumulation, the mean maximum waterstorage was 10.5mm, the highest was up to 20mm.Sub-alpine dark coniferous forest ecosystem showed a deep soil layer, a low bulk density, ahigh soil porosity, a fast infiltration velocity and a high soil water holding capacity. The meanvalues of these parameters were respectively 80～120cm, 0.96g/cm~3, 65%(total porosity)and11% (noncapillary), 2.63 mm/min(saturated soil infiltration rate), 414.3mm(0～40cm soil waterstorage)and 51.4mm(0～40cm noncapillary water storage). Interestingly, these parametersshowed slightly differences among different communities while significant differences amongdifferent soil depths. From July to October, the mean volumetric soil moisture content in thecatchment varied from 0.59 to 0.66. The highest soil moisture content occurred in thesubsurface soil layer while the lowest soil moisture content in below 45cm soil depth. Withascending of altitude, increasing trend was firstly found in soil moisture content (SMC),however, when altitude exceeded 3700m, SMC showed inversely decreasing trend. Comparedwith southwest-aspect slope, northeast-aspect slope showed higher SMC in 0～30cm soil depthwhile lower SMC in soil depth below 30cm. Soil moisture of the lower slopes were higherthan those of upper slopes. The coefficient of variability (CV) of soil moisture at catchmentscale was 0.22～0.41. The CV increased with increasing SMC while decreased with increasingsoil depth. The CV at northeast-aspect was higher than that at southwest-aspect, at lower slope higher than that at middle slope and upper slope.Annual actual evapotranspiration (ETa) in sub-alpine dark coniferous forest ecosystem wascaculated by using modified Priestley-Taylor formula and Rithchie (1972) method, was350.8mm, growing season, the seasons when this study were conducted, was found accountedfor 55% of the annual ETa. Significant difference was found in ETa of different communities(p＜0.001), the highest ETa occurred in the grass-bamboo-fir (422.0mm), followed by themoss-rhododendron-fir(363.1mm), the grass-bamboo-fir(355.6mm)and the moss-bamboo-fir(323.4mm), the lowest LAI value was in the rhododendron shrubs (248.4mm). Total solarradiation is the predorminant factor of evapotranspiration. ETa was relatively lower thanexpected (about 35% of rainfall), this may due largely to a fact that more rainy and foggy daysand less sunlight hours and solar radiation in growing season in this area.Wetness index at the bottom of the catchment was higher than that at hill slope, at the middleelevation higher than that at the lower elevation and higher elevation, and at northeast-aspecthigher than that at southwest-aspect. The highest wetness index occurred in the rhododendronfir stands, followed by the bamboo-fir stands, the lowest wetness index was in rhododendronshrubs. Moreover, wetness index increased with the increases of precipitation, solar radiationand vegetation density.Sub-alpine dark coniferous forest ecosystem showed strong capacity of rainfall interceptionand soil water storage, with a sum of 89.5mm, including 86% of soil, 12% of litter and mossand only 2% of canopy. Different sub-alpine dark conifer forest types showed significantdifferences in their canopy interception, litter and moss interception and soil water content andevapotranspiration. The decreasing sequence of the total capacities are as follows:moss-bamboo-Minjiang fir, grass-bamboo-Minjiang fir, moss-rhododendron-Minjiang fir,grass-rhododendron-Minjiang fir. As expected, strong linear relationship was found betweenleaf area index (LAI) and maximum canopy interception. With the increasing vegetationcoverage and LAI, maximum canopy interception and evapotranspiration increase whereas soilmoisture decrease. When vegetation coverage is higher than 70% or LAI value greater than 4.8,the increase in evapotranspiration is not evident.更多还原