Quantitative Analysis Of Water Conservation Function Of The Spruce Forest In Urumqi River Basin Based On 3S Technology

Water conservation is the important ecological function of the forest. In the past, the study on water conservation function of forest ecosystem mostly based on stand scale or the slope scale, quantitative watershed scale water conservation function of forest ecosystem, not only is the management of water resources demand but also is the bottle neck of forest water conservation function for many years. Quantitative assessment problem around the water conservation function of natural spruce forest in Urumqi river basin, this article focuses on the following four aspects research:(1) quantitative study on the relationship between spruce forest and terrain factors(elevation, slope, slope direction);(2) quantitative study on the potential distribution area of spruce forest;(3) quantitative study on forest change and hydrological response;(4) quantitative assessment of basin water conservation function based on InVEST model. The above research will provide a scientific basis for the rational management of the spruce forest in Central Tianshan Mountains and the objective assessment of the water conservation function of the watershed scale. The main conclusions are as follows:The relationships between the topographic factors(slope, aspect, elevation) and spruce forest in the Urumqi river basin located at middle Tianshan Mountain were quantified analysis by 3S(GIS?RS?GPS) technologies.(1) The relationship between spruce distribution area and the elevation fit the weibull function. 83% of the spruce forest distribution at an altitude of 2000~2600 m, an elevation 2200~2400 m is the optimum distribution area;(2) The distributions of different slope spruce forest are conditioned by habitat composite index. The shade slope with the optimal habitat index of 0.7~0.8 have 58.93% of the spruce forest. In addition, the sunny slope with the lowest habitat index of 0.3~0.4 have no distribution of the spruce forest. There are 30.25% of the spruce forest distribute in the northwest and northeast slope.(3) Using Gauss function, the distribution of spruce forest on different slopes can be quantified, 83% of the spruce forest distribute in the slope from 16° to 45°, and 35% of the spruce forest distribute(the maximum frequency distribution) in the steep from 26° to 35°.Based on the field survey data and the GIS spatial modeling technology, the habitat index model was constructed to predict the potential distribution areas of spruce forest.(1) The study area has 7.01×103 hm2 of forest lower bound, glade and half shady slope area which accounted for 6.37% of the study area can become future potential distribution area of forest by habitat index;(2) The difference of the potential distribution area and the distribution area is not significant, and the difference of no spruce forest area is very significant.Quantitative analysis the hydrological response to forest changes in the study area based on SWAT model.(1) The calibrated SWAT model can well simulate the monthly flows;(2) The model has higher simulation precision, the most sensitive parameters influencing model was CN2 based on the actual distribution of forest land condition. The R2 and Ens of calibration and validation periods were higher than 0.85, the relative errors |Re| were all less than 5%;(3) In the same climate condition, the spruce forest change in wet year, normal year, dry year showed a linear correlation with runoff, spruce forest area increased by 1%, runoff were reduced 0.22 m3/s, 0.21 m3/s, 0.16 m3/s, respectively; And the runoff increased more significantly in wet year and normal year;(4) With the decrease of the area until disappear of spruce forest(the forest land cover was reduced from 14.54% to 0%), the variation of the runoff variation coefficient and the fluctuation range of the times increased gradually, and the fluctuation range of the runoff will expand 6.16 times.Quantitative studies of water conservation function of the watershed scale based on InVEST model.(1)The InVEST model can well assessment the water conservation in watershed scale. By simulating the invest model, the Urumqi River Basin of spruce forest total water conservation is 4.93×106 m3, accounting for 20.46% of the total water conservation in study area(2.41×107 m3), and the average water conservation depth of forest area is 54.25 mm.(2) The contribution rate of water conservation in spruce forest is closely related to forest area, the contribution rate of water conservation in the slope, aspect and elevation is consistent with the spatial distribution pattern of the spruce forest. And per hectare of water conservation, with the altitude increased first increased and then decreased, with the increase of the slope decreases, more close to the north aspect, the water conservation ability is stronger.(3) For different land use types in study area, the spruce forest showed the greatest capacity reached to 544.78 m3·hm-2, with increasing coverage of spruce forest, the total water conservation, average water conservation depth and unit area conservation showed increasing trend, spruce forest area increased by 1%, the total water conservation of study area and forest area were increased 0.437×106 m3, 0.522×106 m3, respectively. Therefore, to strengthen the protection and management of spruce forest, forest plays to make sustained and stable water conservation ecological services function.