A global data base of soils is an important tool in trace gas studies. Soil fertility and soil chemical and physical parameters play an important role in the production and emission of trace gases. Extrapolation of point measurement data for fluxes can only be done on the basis of a reliable soil data base. The best data base available is the FAO/Unesco Soil Map of the World which is available as a map or as a digital data base. The information on the map is however, not reliable in many parts of the world. Much new in information has become available since its compilation. A major problem with the map is that it represents codes for soil associations, and information on texture of the topsoil for the major component of the association only. Only experienced soil scientists are capable to translate information included in the descriptions of the map units into terms of controlling factors of trace gas fluxes. A new soil data base, the Soil and Terrain Digital Data Base of the World at 1:1,000,000 scale, is being developed. This data base will contain, where available, all the basic information needed for trace gas studies. In the final part of section 3.1 a brief description is given for 18 Major Soil Groupings, which are associations of the Major Soils occurring on the FAO/Unesco Soil Map of the World. These general descriptions include information on climate natural vegetation and broad physical and chemical soil properties. There are many maps and digital data sets of vegetation available. Differences in the classification system used cause difinitional problems which make intercomparisons difficult. Many maps and data sets present the theoretical climax vegetation and not actual land cover or land use. For most trace gases the type and intensity of use of land determines the flux rate and pattern. The lack of good data on land use explains the uncertainty of the estimates of sources of e.g., wetland rice cultivation in the case of methane, and cultivated land in the case of nitrous oxide. At present, there is no good system for classifying the different types of land use at a global scale. Some attempts to develop such a scheme have been made, but most classifications have local or regional value only. There is great controversy concerning the global annual deforestation rate of tropical forests. Estimates of global forest destruction for permanent agriculture range from 10 to 20x10 hoch 10 Quadratmeter y hoch -1, much of it in the Amazon region. Global reforestation is about 14.5x10 hoch Quadratmeter y hoch -1. There now remains only about 10x10 hoch 12 Quadratmeter of tropical forest. The figures reported for shifting cultivation show even greater variability than those for permanent clearing. Most of the data base is unreliable. Careful comparison learns that there is great controversy between the various estimates concerning the .
