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Sensitivity Analysis of Ecological Models To Soil Information

Soil information is essential to many terrestrial ecological modeling and management activities. Polygon soil maps produced from soil surveys are currently the major source of information on the spatial distribution of soil properties. However, there are some major problems regarding the use of current soil maps in geographic analysis and especially in geographical information systems (GIS).

In the generation of soil information for geographic analysis, the area of a soil polygon is assigned with the soil property values of the soil type as which the soil polygon was labeled. The so-generated soil property information inherits two types of errors of soil maps: the commission errors and attribute errors. The commission errors occur when a minimum mapping size was imposed during the soil map generation process due to the map scale. Areas smaller than the minimum mapping size were "filtered" out ( Fig.1 ). On soil maps, areas within a soil polygon have the same soil property values. In other words, the spatial variation of soil properties within a soil polygon is not maintained in a GIS database. As a result, the variation of soil property values along a transect is perceived as a step function rather than a gradual and continuous variation ( Fig. 2 ). Soil property maps generated from conventional soil maps inherit the exact spatial patterns of soil polygons on soil maps ( Fig.3 ).

Zhu et al (1996) have developed a soil inference model, SoLIM (Soil Land Inference Model). The method employs an expert system approach and infers soil property information under fuzzy logic. Soil information is express as SSVs. This fuzzy representation together with the raster data model allows the representation of spatial gradation of soil property values ( Fig. 4).

In this project, the impact and severity of soil information derived from soil maps and soil information derived from SoLIM on the result of hydro-ecological models will be studied and discussed.



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