| Abstrakt: |
1. During the extremely hot and dry summer of 1976 synecological investigations in the Jurineo-Koelerietum of the Mainzer Sand, Western Germany, have been practiced. Measurements have been done on an extended dune in the southern part of the terrain. The annual mean temperature of this area is 10°C, the precipitation 515 mm. 2. The diminution of this area with its steppe vegetation by anthropogenic changements is demonstrated. The topographical, geological and climatical situation is characterized. Soils in the area are no climax of soil formation. They must be looked upon as a preliminary final station of soil development. 3. Types of life forms and radication of the characteristic plants are described. The four aspects during the vegetation period of the Jurineo-Koelerietum are: 1. Aspect of early spring with therophytes. 2. Aspect with Alyssum arenarium ssp. gmelinii and Onosma arenarium in May. 3. Aspect of Jurinea cyanoides in summer. 4. Aspect of Salsola kali ssp. ruthenica in September. 4. Diameter of grains of sand, volume of pores and MWK values have been determined on the north and south slope and on the top of the dune with Jurineo-Koelerietum. 5. Changements of water contents of the soil during the day were very extreme in the rainless period. Differences in soil water are significant between the rainless summer and the period with precipitation in autumn. Main changements of soil water take place to a depth of 25-30 cm. They are of great importance for all plants with root systems below the surface. 6. Contents of humus are different between north and south slope and the top of the dune with Jurineo-Koelerietum. Humification has been stated to a depth of 30 cm on the north slope. 7. H+ concentration is diminishing with increasing depth in the rhizosphere of the Jurineo-Koelerietum. Values vary between pH = 7.95-9.3 in solution of H2O. 8. Microclimatical measurements in the open herb layer of the Jurineo-Koelerietum show small differences in dependence of exposition and height in the xerothermic habitat but there are good differences between clear, rainy and those days with a changement of sunny and rainy periods. The highest temperature of soil measured in the extremely hot summer of 1976 was 63.8°C in a depth of 1 cm. |
