Digital Ecological Model (DEM) is a platform developed with Java. It consists of six components: DEMGIS, DEMTSA, DEMSTA, DEMMOD, DEMVIEW, and DEMAPPLET. DEMGIS features major functions of geographic information system (GIS), such as building digital elevation model, managing geo-referenced database, translating vector data into raster data, and generating geographic graphs with different projections. DEMTSA is used to interpolate the scattered climatic data into raster data, by means of trend surface analysis (TSA) method and interpolation method. As a plug-in for GIS, DEMSTA provides some widely used statistic methods. DEMMOD is a platform for building process-based landscape model. It provides a visual interface-Visual Programming Interface of Digital Ecological Model (DEMVPI) for ecologists to 'write' and record the models in an interpretation language-Ecological Description Language of Digital Ecological Model (DEMEDL). Ecological Model Interpreter of Digital Ecological Model (DEMEMI) is responsible for compiling the programs written in DEMEDL, running the model and displaying the results. DEMVIEW is a tool for viewing and editing some geographic graphs. DEMAPPLET can link a Java applet with geo-referenced database and display the simulation results on the Internet. All the codes of DEM were compiled into Java application programs, and some of the programs are available on the Internet as Java applets. As a case study, amended Penman's method was used to calculate the potential evapotranspiration and aridity index of China, under present situation and three prescribed climate scenarios, which include raising mean temperature by 1.5, 3.0 and 4.5℃, and raising precipitation by 10%, to assess the potential impacts of global climate change on China water condition.

A model of stomatal conductance was developed to relate plant transpiration rate to photosynthetic active radiation (PAR), vapour pressure deficit and soil water potential. Parameters of the model include sensitivity of osmotic potential of guard cells to photosynthetic active radiation, elastic modulus of guard cell structure, soil-to-leaf conductance and osmotic potential of guard cells at zero PAR. The model was applied to field observations on three functional types that include 11 species in subtropical southern China. Non-linear statistical regression was used to obtain parameters of the model. The result indicated that the model was capable of predicting stomatal conductance of all the 11 species and three functional types under wide ranges of environmental conditions. Major conclusions included that coniferous trees and shrubs were more tolerant for and resistant to soil water stress than broad-leaf trees due to their lower osmotic potential, lignified guard cell walls, and sunken and suspended guard cell structure under subsidiary epidermal cells. Mid-day depression in transpiration and photosynthesis of pines may be explained by decreased stomatal conductance under a large vapour pressure deficit. Stomatal conductance of pine trees was more strongly affected by vapour pressure deficit than that of other species because of their small soil-to-leaf conductance, which is explainable in terms of xylem tracheids in conifer trees. Tracheids transport water by means of small pit-pairs in their side walls, and are much less efficient than the endperforated vessel members in broad-leaf xylem systems. These conclusions remain hypothetical until direct measurements of these parameters are available.