| Jinyun Mountain is located in the end of the Three Gorges Reservoir and forests in this region play an important role in ecological and hydrological functions.This dissertation takes the typical forest stands in Jinyun Mountain as the research object.According to the principle of water balance,positioning observations of canopy interception loss,water holding capacity of shrub-grass layer,litter-holding and soil water storage,forest evapotranspiration,surface runoff and interflow at each level were conducted on slope scale.The distribution of hydrological components and characteristics of water balance in different forest stands were definited.Moreover,the relationships between hydrological process and non-spatial and spatial stand structure parameters were analyzed to reveal the mechanism of the influence of stand structure characteristics on hydrological process.The purpose is to provide scientific basis for the construction and management of protective forests in Jinyun Mountain and even the whole Three Gorges Reservoir area.The main results were as follows:(1)The structure characteristics of typical forest stands were systematically analyzed.The diameter distribution of most forest stands is inverse J-shaped,which belongs to the typical diameter structure of uneven-aged forests;there are great differences in tree height structure,and the proportion of trees in different forest layers is different;coniferous-broad-leaved mixed forest has a significant effect on improving species diversity;the leaf area index(LAI)ranges from 1.78 to 3.85,with the largest in coniferous-broad-leaved mixed forest;the average neighborhood comparison of forest stand is between 0.35 and 0.65,and most forest stands are in the middle state;the mixing degree of Jinyun Mountain is higher as a whole,and most of the forest stands reach the intensity or extreme intensity mixed;most of the trees in the forest were randomly distributed(W=0.5).There are only three forest stands were random distribution and the others were all aggregated distribution.(2)Features of hydrological process components distribution and water balance were systematically analyzed.The spatial variation coefficients of throughfall were between 5.7%and 16.I%,and pure bamboo stand were the largest.The order of stemflow for different tree species is moso bamboo>broad-leaved tree species>coniferous tree species.The average throughfall rate ranged from 72.8%to 83.2%.Stemflow rate ranged from 0.5%to 11.0%.The interception rate ranged from 13.3%to 26.2%.The rainfall partitioning is significantly correlated with rainfall amount and intensity.The canopy interception of 9 typical stands was simulated by Gash model,with the relative error of simulation ranging from 8.9%to 24.5%.The water holding capacity of shrub and grass layers is very small,ranging from 0.09 mm to 0.33 mm.The maximum water holding capacity of litter ranges from 1.24 mm to 2.74 mm.There were significant differences in soil particulate matter composition,soil bulk density,porosity,soil infiltration capacity and soil water storage under different forest stands.Soil moisture has obvious seasonal variation with the precipitation.The variation range of soil surface moisture is the largest,followed by the lower layer,and the variability of water content in the middle layer is the smallest.The total soil water content of bamboo stands is the highest.The sapflux density of broad-leaved species larger than coniferous species on the whole.Among the meteorological factors,solar radiation had the greatest effect on sap flux density,followed by soil water content and VPD.The total transpiration of typical coniferous broad-leaved mixed forest and evergreen broad-leaved forest in the growing season was 255.2 mm and 290.4 mm,accounting for 24.4%and 27.8%of the rainfall in the study period,respectively.The daily evaporation of litter was 0.28-0.67 mm.The total evaporation of litter water in the growing season was 46.6-118.1mm,accounting for 4.5%-11.3%of the rainfall in the study period.The average daily evaporation of soil moisture is 0.7-1.4 mm,the maximum daily evaporation is 6.8-13.6 mm,and the total evaporation of soil moisture in the growing season is 142.6-297.9 mm,accounting for 13.6-28.5%of the rainfall.The total evapotranspiration of coniferous broad-leaved mixed forest and evergreen broad-leaved forest were 467.0 mm and 479.6 mm,accounting for 44.7%and 45.9%of the rainfall,respectively.The components were vegetation transpiration>soil water evaporation>litter water evaporation.The surface runoff coefficients of typical forest stands ranged from 0.052 to 0.254,the interflow coefficients ranged from 0.030 to 0.451,and the total runoff coefficients ranged from 0.201 to 0.390.Surface runoff and interflow were positively correlated with rainfall amount and intensity.The generation time of surface runoff and interflow were both behind that of rainfall,and the shrub forest was the earliest.Among the water balance items in the growing season(April-October),evapotranspiration is the largest output item,accounting for about 70%of rainfall,followed by runoff(40%)and soil water storage has little change.The equilibrium terms of the two typical stands are negative,that is to say,the rainfall during this period cannot meet the needs of plant growth,and the water recharge from external or deep soil is 118.6 mm and 171.5 mm,respectively.(3)The effects of stand structure characteristics on hydrological process were revealed.The interaction between rainfall characteristics and stand structure has an impact on canopy interception process.The LAI was significantly associated with interception loss for heavy rainfalls(>25mm).Significant relationships existed between mingling index,throughfall,and interception loss for light rainfall(drizzle).Significant relationships existed between uniform angle index and interception loss for light and heavy rainfalls.Moreover,significant relationships only existed between LAI,neighbourhood comparison,uniform angle index and throughfall and interception loss for rainfall intensity<lmm/h.Therefore,to study the influence of stand structure on hydrological process,rainfall patterns must be taken into account.Spatial structural characteristics(that is mixing index and uniform angle index)play an extremely significant role in the production of stemflow under all rainfall conditions.The stronger the mixed degree of stand,the more unfavorable for stem flow generating;the larger the stand angle scale,the more aggregated the distribution of trees,the larger the gap between trees,which is conducive to the generation of stem flow.The transpiration rate of a single tree is not only affected by the DBH,but also by the spatial position of the tree in the forest.The sap flow rate of dominant tree species is higher than that of inferior tree species.On the contrary,the sap flow rate of dominant tree species is lower than that of inferior tree species,and the sap flow rate of clustered tree species is higher than that of uniform tree species.Canopy density,litter reserves,uniform angle index and mixing index had significant effects on soil water storage.The direct effects were canopy density>spatial distribution pattern of trees>mixing degree>litter reserves.While species diversity of tree layer,litter reserves,uniform angle index and mixing index had significant effects on surface runoff.The direct effects were as follows:neighborhood comparison>distribution pattern of trees>diversity of tree layer>litter reserves.The stand structure parameters that have significant effects on interflow were species diversity of herbaceous layer,soil thickness and litter reserves.The direct effects were as follows:litter reserves>soil thickness>species diversity of herbaceous layer.It can be seen that spatial structure characteristics have significant effects on soil water storage and surface runoff. |
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