Spatial Scale Effect And Optimization Of Basin’s Biocapacity

The paper is conducted under the theoretical guidance of ecological economics, landscape ecology, sustainable development and Ecological Footprint. Aiming at solving the deficiency in the study of spatial scale effect on biocapacity and its optimal design, the paper firstly made an quantitative assessment of the basin’s biocapacity for two watersheds, i.e. Shiyang River Basin and Jinghe River Watershed based on the land use information extracted from Landsat TM images on different raster scales (with resolution 30m,60m,120m,240m,480m,960m,1920m,3840m, 7680m in linear multiplication scales) by the resampling method of ArcGIS9.3. It also analyzed the spatial patterns of biocapacity and their scale effect by introducing the global and local spatial autocorrelation indexes and lacunarity index. Secondly, setting the Shiyang River Basin as a case study, the paper established the optimization probability model of the basin by applying the binary logistic regression model and cellular automaton, and studied the optimization of biocapacity under three different land use evolutionary rules and two distinct neighbor structures (four neighbors and eight neighbors).The main conclusions of this paper are as follows:1. Studies on the spatial scale effect(1) According to the spatial distributions of biocapacity under various raster scales, the spatial patterns of biocapacity of Jinghe River Watershed and Shiyang River Basin are similar within the raster scales from 30m to 480m, and this similarity disappears gradually after raster size exceeds 960m (960m to 7680m).(2) The global spatial autocorrelation indexes of Jinghe River Watershed and Shiyang River Basin on different raster scales show distinct characters:positive spatial autocorrelation and negative spatial autocorrelation. The global spatial autocorrelation indexes in the two watersheds decrease with the increment of raster scale reflecting relatively strong dependence on spatial scale. An evident logarithmic relationship can be seen further between autocorrelation index and raster scale size.(3) With the increase of raster scale, the local distributions of the dissimilar and similar region of biocapacity of the two watersheds vary significantly, which demonstrates that the spatial resolution of remote sensing images would greatly influence the local autocorrelation. This means the spatial autocorrelation of biocapacity also has strong dependence on scale.(4) The various land use types of Jinghe River Watershed and Shiyang River Basin serve as the carrier of biocapacity, on different raster scales, the lacunarity indexes show different change trend with the increase of raster scale, and the lacunarity index also shows an obvious negative logarithmic relationship with the land use size.(5) With the increasing of raster scale, the biocapacity shows a decreasing trend with Jinghe River Watershed while it increases first before following a decreasing trend for Shiyang River Basin. The biocapacity of the two watersheds show strong scale dependency and the land use types which accounts for relatively large percentages of land use size also demonstrate an evident dependency on scale. Specifically, in the transform of land use size between different raster scales, a bigger change can be seen for the land use types that occupy large areas. This scale dependency indicates that the spatial resolution of the data of land use in the calculation of biocapacity would exert impacts on the assessment results of regional sustainable development situation.2. Study on the spatial optimization(1) The correlation between the spatial distribution of probability of different land use types and the main influencing factors in Shiyang River Basin are analyzed by binary logistic regression model, which clarifies the contributing ratios of various influencing factors to different land use types. The result shows that the altitude, slope and population density are the key factors that constrain the spatial distribution of probabilities of different land use types. The spatial patterns of probability of different land use types under the constraint of the eight influencing factors are also analyzed. Furthermore, based on the spatial distribution of probability and the probability of the neighborhood, the optimization model of biocapacity under the constraint conditions of Shiyang River Basin are constructed.(2) The optimization study of the biocapacity of Shiyang River Basin shows that under three distinct evolutionary rules, the eight-neighbors can increases much more transformation among various land use types than the four-neighbors, and the effect of increasing or decreasing the area and the biocapacity of various land use types is the same. However, the magnitude of change of land use size and biocapacity are changed, and the transformation degree varies with the alternation of evolutionary rules.(3) Under different evolutionary rules, the transformation between various land use types is different and the transformation ratios also vary resulting in various transformation degrees of the area and biocapacity of land use types. The area and biocapacity of grazing land decrease under the first two evolutionary rules based on either four-neighbors or eight-neighbors calculating strategies, but they increase under the third evolutionary rule. Forest land keeps invariably increasing in the area and biocapacity under the three rules; the biocapacity of cropland and the overall biocapacity of Shiyang River Basin both increase under the first two evolutionary rules which are supposed to be due to the sacrifice of grassland and forest, and decrease under the third rule in which the areas of grazing land and forest land increase by a ratio of 3.37% and 12.91% respectively, while cropland shrinks just as returning cropland to forest land or grazing land.This study reveals the characters of the distribution of basin’s biocapacity and its dependency on spatial scale, and enriches the theory and methods in the spatial analysis of basin’s biocapacity; the optimized spatial patterns of the biocapacity of Shiyang River Basin are obtained under various constraining conditions by using three different evolutionary rules. It would provide scientific bases for the overall treatment of watershed ecological environment, sustainable management of natural resources and the constitution of forward-looking policies of sustainable development.