| For understanding space changes of the hydrological elements, to quantify its impact onthe hydrological processes and the slope scale effect. Based on the measurements of vegetationstructure and site factors of the typical slope andmain vegetation types,and the observations offorest ecological and hydrological processes using the traditional hydrology method from2012to2013two years growing season (May to October) in Xiangshuihe watershed of LiupanMountains, Ningxia. We quantified the hydrological effects of vegetation and it’s slopedifference and analyzed the slope scale effect. This study is helpful to understand thehydrological effect of vegetation system structure and its formation mechanism form samplescale to slope scale, and to promote the development of forest ecological hydrology theory, andto provide scientific guidance for regional forest integrated water management.1. The differences of vegetation structure characteristics and evapotranspiration invegetation typeThe structure characteristics of main forest type in Xiangshuihe watershed are different.Significant differences were diameter at breast height and tree height. The season change trendof canopy LAI of Pinus armandii forest, Betula platyphylla forest and Quercus liaotungensisforest was similar, the dynamic of canopy LAI was showed for growing rapidly rising in earlygrowth stage, remain stable in mid growth stage, and slow decline in later growth stage. but theseason changing scale of canopy LAI of P. tablaeformis forest was small.The forest soil types are mostly black brown soil and gravel content is higher inXiangshuihe watershed. The soil characteristic of B. platyphylla forest, P.tablaeformis forest,P.armandii forest and Q.liaotungensis forest was similar, bulk density was0.83、1.04、0.79、1.14g·cm-3, total porosity was66.5、59.6、68.0、56.4%, field capacity was47.1、32.9、62.4、35.2%in0-100cm soil layer, respectively.Rainfall is507.2mm in the growing season (May11to October18) of2012inXiangshuihe watershed. The results showed that forest evapotranspiration and its components difference were mainly affected by species composition, canopy density, the stand verticalstructure. The stand evapotranspiration of P. armandii forest, B. platyphylla forest,Q.liaotungensis forest, P. tablaeformis forest and Larix Principis rupprechtii forest were413.2,480.7,389.0,377.6,541.4mm, respectively accounted for81.5,94.8,76.7,74.4and106.7%ofthe rainfall at the same period, but it’s components are different.2. The differences of Larix Principis rupprechtii forest structure characteristics andevapotranspiration (components) in different densityDifferent density of Larix Principis rupprechtii forest were thinning in2007(1811、1556、1134、1033、844tree·hm-2), the average tree height of different density of Larix Principisrupprechtii forests were similar(13.8～14.8m), but the DBH is increased with the decrease ofstand density (16.3-18.1cm).The season change trend of LAI of Larix Principis rupprechtiiforests with different density were similar, the dynamic of canopy LAI was showed forgrowing rapidly rising in early growth stage, remain stable in mid growth stage, and slowdecline in later growth stage. and LAI were positively correlated with forest density.The soil hydrological-physical properties of Larix Principis rupprechtii forests withdifferent density had certain difference, but there was no significant change rule.The evaporation of L. Pricipis-rupprechtiis with the density of1811、1556、1134、1033、844tree·hm-2were614.9,549.6,531.7,500.7,466.9mm, respectively accounted for121.2,108.3,104.8,98.7and92.0%of the rainfall (507.2mm) at the same period, and the value ofevaporation was positively correlated whit stand density. The results show that thinningtreatment reducing stand density after5years was an observed effective measure for reducingthe stand evapotranspiration.3. The differences of Larix Principis rupprechtii forest structure characteristics andevapotranspiration (components) and slope scale effect in different slpoeHalf-sunny slope as a typical slope was choose that distribution of L pricipis-rupprechtii,DBH had mainly distributed in16-24cm, and an average value of tree height more than11m.The average value of LAI of different slope (top,upper, middle,lower and bottom slope position) was2.97,3.14,3.20,3.19,3.24in growing season, respectively.Moving average increase withthe of level of slope length from the top downward slope.The soil hydrological-physicalproperties of Larix Principis rupprechtii forests with different slope position had certaindifference, but there was no significant change rule.The result showed that stand structurefeatures (Tree height, DBH, LAI) can represent the entire slope forest stand structurecharacteristics when investigating slope length was200m.To evaluate the representation ofstand structure to total slope and change rule stand structure with the slope length in thedifferent slope position, the quantitative relationship was established between the ratio of standstructure in different slope position with slope average value and the slope horizontal distanceform top to bottom.Rainfall is815.9mm in the growing season (May16to October19) in2013, belong to thewet year. The evaporation of L. Pricipis-rupprechtiis in different slope positions (from topslope to bottom slope) were425.7,440.7,449.8,448.8mm,486.1mm, on typical slope,respectively accounted for52.5、54.0、55.1、55.0and59.6%of the rainfall at the same period.Accounting for the proportion of rainfall was decreased obviously, because of effected byrainfall and meteorological conditions. The evapotranspiration and its components existedslope position differences. Interception and transpiration was increase with lower slopepositions, contrary trend of floor evaporation; Total evapotranspiration was increase with lowerslope positions.The effect of forest to hydrological exist slope scale effec. Calculation of the slpoemoving average value of the stand evapotranspiration and its components form top to lower ingrowing season in2013, canopy interception showed reduced first and continue to increaseafter, floor evaporation showed increase first and continue to reduced after, tree transpirationand total evapotranspiration showed continue to increase with the slope horizontal distanceincrease. Compared to the average value, the moving average value of canopy interception, treetranspiration, understory evapotranspiration and total evapotranspiration was respectively lower3.9%(5.6mm), lower9.4%(12.35mm), higher5.6%(9.6mm) and lower1.9%(8.4mm) when slope length was200m.Relationships between ratios of forest evapotranspiration and its components measured ina specific position of a slope to the slope average and the horizontal distance from the slope topwas obtained in this paper. Therefore, the average of an index for a whole slope can beupscaled from the value measured in any given slope position. That would lessen the workloadand improve the accuracy.4. The flow characteristics of different vegetation typesWater balance calculation of forest plots in growing season in2012, the results showed:not all stand sample has water output. The capacity of water output of P. armandii forest and Q.liaotungensis forest was16.6and54.7mm, water output of P. tablaeformis forest and B.platyphylla forest was-6.6and-82.1mm, consumption of soil moisture.The water flow of L. Pricipis-rupprechtiis forest with density from high to low were:33.1,31.9,68.5,85.9, and89.5mm, runoff increased by170.3%when density decreased by53.5%.The results showed that thinning treatment reducing stand density after5years was an effectivemeasure for increasing the runoff production.The water flow of L. Pricipis-rupprechtiis forest in top, middle and bottom slope positionwere353.7,344.4,301.4mm respectively in2013year growing season, runoff decreased fromtop slope to bottom slope.5. The relationship between leaf area index and hydrological processBetter correlations between LAI with other forest structure, and LAI was direct effecedthe hydrological process of stand. In order to understanding the effected of forest standstructure for hydrological processes. The correlation analysis was used the average value ofLAI in growing season and data of hydrological process in2012, the results showed: the totalevapotranspiration, canopy interception and tree transpiration was positively related with leafarea index (LAI), and the correlation coefficients (R2)were respectively0.61,0.50and0.45.However, understory evapotranspiration was negatively related with leaf LAI, with a low correlation coefficient of0.12. There was a liner relationship between LAI and forest waterflow and the correlation coefficient (R2) was up to0.58. The results showed that foreststructure characteristics were the important influence factors of forest evapotranspiration andrunoff. |
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