Research On Soil And Water Conservation Function Of Forest Plant Communities In Chongqing Simian Mountains

On the basis of field investigations as well as lab experiments, this paper studied the six types of forest plant communities in Chongqing Simian Mountains about the water and soil conservation function of forests at canopy layer, litters layer and the soil layer respectively. Such research tools as statistic analysis method, grey correlation method, fractal theory, analytic hierarchy process, fuzzy mathematics, technique for order preference by similarity to ideal solution and sensitivity analysis were applied to evaluate the water and soil conservation functions and their corresponding degree of sensitivity. Six types of forest plant communities were consequently ranked in terms of water and soil conservation capacity respectively. This paper aims to shed some lights on the establishment of structurally-reasonable, eco-functionally-stable water and soil conservation vegetation communities in Chongqing Simian Mountains and surrounding regions. The primary findings were summed up as follows:Hydrological study on the three functional layers of the different forest plant communities indicated that, given the almost same stand ages and canopy closures, the maximum canopy interception rate is observed in both coniferous forest communities, whereas the lowest was found in broad-leaved forest and warm bamboo forest with relatively lower canopy interception capability under different rainfall levels. Rainfalls retained by the canopy layers account for 15%-25% of the weight of overall branches and trunks. Given similar environmental factors, the broad-leaved tree dominated stands were sufficiently covered by forest litters and relatively higher decomposition intensity, consequently have noticeably better performance than coniferous forest and bamboo forest dominate stands. With maximum water-holding capacity at 5.13-5.65 mm, the litters of broad-leaved forest are capable of conserving throughfall. The soil layers of evergreen broad-leaved forest demonstrated sound water-storage and penetrating capacities, with their average total water storages reaching at 312.99 mm. The soil saturated hydraulic conductivity and soil bulk density and porosity of different forest plants communities is related closely.Soil conservation function was revealed, through study and analysis on the physical properties, anti-erodibilit, anti-sourability and anti-shear strength of the soil in the six types of forest plant communities, the results showed that, different forest plant community has role of improved its forest soil. There are differences in the soil physical properties of different forest plant communities: Compared with the soil taken from the two types of coniferous forest communities and bamboo forest community, soil taken from the three types of broad-leaved communities has lower density, measured at 1.02-1.11g/cm3 on the 0～20cm layers; the non-capillary porosity is relatively higher, falling at 15.81%-7.66%; soil aggregate structure of the three kinds of broad-leaved forest communities is significantly greater than the two types of coniferous forest communities and bamboo forest community. Soil anti-erodibilit and time are into two polynomial function relation, soil anti-sourability and flush time are into index relation. The best soil anti-erodibilit and anti-sourability are from evergreen and deciduous broad-leaved mixed forest and warm bamboo forest respectively. The soil anti-erodibilit and anti-sourability at different levels of soil in the same soil profile decline with the increase of the soil depth. In a vertical pressure, soil anti-shear strength of different forest plant communities were in a linear relationship to vertical stress. There are differences in the change of the soil internal friction angle and cohesion and pastes. The value of soil internal friction angle and cohesion and pastes of the six types of forest plant communities ranged respectively between 21.37°～27.87°nd 5.54-38.91KPa. Soil anti-shear strength and root density are in a linear correlated. The anti-erodibilit, anti-sourability and anti-shear strength of different forest plant communities are related to soil physical properties such as soil density, whole-capillary and non-capillary porosity. Comparative studies showed that broad-leaved forest communities outdo both coniferous forest communities and bamboo forest community in terms of the mentioned three indicators.The anti-erodibilit indexes, anti-sourability indexes, internal friction angle and cohesion and pastes the value of resistance of the anti-shear strength and sticky indexes of the six types of forest plant communities ranged respectively between 62.0%～85.0%,5.56～28.94,21.37°～27.87°and 5.54～38.91KPa. Comparative studies showed that broad-leaved communities outdo both coniferous forest communities and bamboo forest community in terms of the above-mentioned three indicators.Based on systematical analysis of the characteristic of soil and water conservation of different forest plant communities in Chongqing Simian Mountains and by means of fuzzy mathematics, analytic hierarchy process, MATLAB software-based AHP evaluating tools and models and ideal-point decision-making principles, so that comprehensive assessments could be carried out to rank the six types of plant communities in terms of their corresponding water and soil conserving capacities. It was concluded that the water and soil conserving functions of the six types of plant communities rank as: evergreen broad-leaved forest>deciduous broad-leaved forest>evergreen and deciduous broad-leaved mixed forest>warm coniferous forest>warm bamboo forest>temperate coniferous forest.