| Qilian Mountains is not only the headwaters of Heihe River,but also one of key water-processing area and water-supplying areas of the whole valley,having a decisive role in the sustainable development of water resources.Picea crassifolia forest is an important forest type for conservation of water supply in Qilian Mountains.The structure and growth conditions of Picea crassifolia forest have crucial impacts on mountain hydrological processes.However,there is a complex relationship between forest and water.Water,the most active factor in forest ecosystem,is the main carrier to participate in and affect the material circulation and energy flow of forest ecosystem,and determines the existence,restoration,operation,stability and development of the forest.Vice,forest plays an important role in the utilization,storage,transformation and consumption of water,as well as the formation of runoff.Slope is not only the basic spatial unit of forest vegetation and water resources,but also the basic spatial unit of forest planning and management.Therefore,it is necessary to understand the characteristics of water and vegetation structure under the specific topography.Therefore,it is need a deep understanding of the influence of soil water storage changes along the slope on forest structure.Which will help to realize the sustainable development of forest and water,and provide the basis for the establishment and verification of the model at the basin scale.In this paper,we selected the typical Picea crassifolia forest slope in the Pailugou small watershed of Qilian Mountains to study the change of soil water storage along the slope and its effect on the forest structure.There are 15 soil moisture observation points and 10 Picea crassifolia forest plots were set up at the slope on different slope positon?upper slope,middle-upper slope,middle slope,middle-lower slope,lower slope?.This paper analyzes the characteristics of the forest structure along the slope,the influence of the moss layer on the hydrological process,the variation characteristics of the soil moisture along the slope,and the relationship between the stand structure and site moisture conditions.The main results were as follows:1.Moss layers can dramatically reduce the spatial variability of soil moisture storage.The spatial variability of the soil moisture content was 62.2 mm in the sites without moss layers,and the coefficient of variation?CV?in spatial change was 17.3%.The CV in the sites with moss layers was 2.3%.The sites with moss layers only account for 1/7.5 of the without moss layer covered.So spatial difference was very significant?sig.<0.001?.The CV of the sites with moss layers was significantly lower than that of sites without moss layers?sig < 0.05?.The CV of the sites with moss layers was significantly lower than that of sites without moss layers?sig < 0.05?in any weather conditions?without rain,with light rain or strong rain?.1.The mean values of soil moisture of middle slope position is highest in the whole growing season,average monthly soil water storage in 5-9 months and under different weather conditions.The average soil water storage in the growing season showed a single peak change from top to bottom slope position.The amount of soil water storage in middle slope positon was the highest?201mm?,and the highest slope positon was the least?159mm?.The average soil water content in the middle and middle-lower slope position of 5-9 month was higher than that of other slope positon.In any weather conditions?without rain,with light rain or strong rain?,soil water storage of different soil layers in the middle and lower slope was higher than that in other slope positions.3.Stand density and basal area changed with a curve along the slope with peak values of 2013 tree·ha-1 and 29.6 m2·ha-1.Tree heigh,diameter at breast height and Crown width were like an M curve along the slope.That means that the stand structure of those three on upper middle slope and lower middle slope were better than other slope positions.The correlation coefficient between basal area and soil water storage volume was 0.8997,sig=0.0387,and there was significant correlation between them.There was no significant correlation between other stand structure indexes and soil water storage.By comparing the correlation between environmental factors,soil water storage is mainly affected by soil thickness and slope position?elevation?.Therefore,slope position and soil thickness affect the change of forest stand structure by influencing the redistribution of soil water storage. |
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