Characteristics Of Main Site Factors And Their Effects On Spatial Distribution Of Trees In The Mountain Areas Of Central And Southern Of Shandong Province,China

The mountainous area in the central and southern of Shandong Province is the most dangerous area of soil and water loss and potential soil erosion in China.According to the characteristics of site factors," match species with the site " and scientific afforestation can improve the survival rate of trees,which is an important way to control soil and water loss.Therefore,the study of site factor characteristics plays a key role in guiding vegetation restoration.Soil erosion is dominated by water erosion,and the soil is shallow with the characteristic of "soil-rock binary structure" in the mountain areas of central and southern of Shandong Province.In addition,shallow soil combined with drought,rainstorm and catchment of bare rock will increase runoff,which will intensify soil thinning and rocky desertification.Soil thickness affects the microhabitat conditions of vegetation growth,such as the storage space capacity and supply of soil moisture and nutrients.Therefore,soil thickness is one of the main factors in the classification of afforestation site conditions in earth-rock mountain region,and it has become an important basis for afforestation planning and design in the near natural area because of the heterogeneity of soil thickness on slope surface.However,the complex environment in this region makes it difficult to obtain soil thickness directly.Therefore,it is urgent to explore a low-cost and rapid method to determine soil thickness,which makes the study focus on spatial distribution characteristics of trees based on soil thickness and their responses to major site factors.Spatial heterogeneity of site factors such as soil thickness result in the difference of site conditions of forest,which makes the spatial distribution of trees is not uniform.Therefore,exploring distribution of trees on the basis of soil thickness and their respond mechanisms of main site factors is the important basis of preventing soil and water loss and guide of near natural afforestation.This study analyzed characteristics of the main site factor in the mountain areas of central and southern of Shandong Province,selecting Yishui County and basin of Qianshiwu as the representative area with the characteristic of "earth-rock dual structure".The spatial distribution of soil thickness was investigated,and the spatial distribution law of soil thickness was analyzed by spatial interpolation and Soil-land Inference Model.The spatial distribution of Pinus tabuliformis Carrière,Populus L.and Robinia pseudoacacia L.was revealed,and the range of habitat conditions such as soil thickness was defined respectively.The main conclusions are as follows:(1)Drought trend and area increased gradually in the mountainous areas in the mountain areas of central and southern of Shandong Province,and Yishui and other counties had the strongest continuous drought trend;the north and southeast of Yishui County and the northeast of Yinan are the most seriously fragmented and the most sensitive.The polarization area with high erosion intensity of soil erosion appears in the areas of Yiyuan,Mengyin and the north of Yishui,etc.Yishui County is one of the typical representatives of the difficult sites in this region.(2)The soil thickness on the slope of Yimeng Mountain area varies greatly,and its range is mostly 5-80 cm,which shows great heterogeneity.There is a significant positive correlation between soil moisture content and soil thickness in 0-40 cm soil layer,which is a quadratic polynomial function relationship.The inflection point of soil moisture content change trend within 0-40 cm soil thickness corresponds to a soil thickness of 17.7cm.(3)Total P,total N,alkali-hydrolyzable N and organic matter can be used as the indicator indexes between soil thickness and soil nutrients.They all show a logarithmic function relationship,and total P has the strongest correlation.(4)Topographic wetness index,elevation and slope are the most important factors affecting the spatial distribution characteristics of soil thickness.Topographic wetness index is positively correlated with the soil thickness,while the elevation and slope are negatively correlated with the soil thickness.(5)According to the results of soil thickness predictive mapping,the method of soil thickness predictive mapping using SoLIM model has a high accuracy in Yimeng Mountain Area,especially in Yishui County.The predictive mapping results of soil thickness based on soil type and land use type both have high spatial accuracy,but the prediction accuracy based on land use type(error 12.77)is higher than that based on soil type(error 15.97).The results show that the SoLIM method is feasible for the predictive mapping of soil properties under complex environmental conditions.(6)In the continuous slope,the maximum aggregation intensity of Pinus tabuliformis Carrière,Populus L.is achieved when the radius is about 76-80 m,and the maximum aggregation intensity of Robinia pseudoacacia L.is achieved when the radius is about108 m.In single slope,the maximum aggregation intensity of Pinus tabuliformis Carrière,Populus L.and Robinia pseudoacacia L.is respectively achieved within the radius range of 30-50 m,23-25 m and 15-28 m.The radius corresponding to the maximum aggregation intensity represents the maximum habitat space required for the three trees in continuous slope and single slope.Meanwhile the resource competition of poplar and Robinia pseudoacacia in continuous slope and single slope is not strong.(7))According to the analysis and ranking of site factors,elevation,soil thickness and topographic wetness index can be taken as important reference basis in the design of near natural afforestation.For Pinus tabuliformis Carrière,Populus L.and Robinia pseudoacacia L.The optimum elevation respectively are 301?508m,138?320m and112?150m,and corresponding positions respectively are on the slope,in the slope and under the slope.The minimum soil thickness of the three tree tree species respectively are20 cm,40cm and 30 cm.The results show that the minimum topographic wetness index of Robinia pseudoacacia L.is the lowest,followed by Pinus tabuliformis Carrière,and the maximum is Populus L..