Climatic Condition at Three Beech Forest Sites in Central Germany

Abstract

Climate is one of the major factors controlling the growth and functioning of plant ecosystems in general and of beech forests in particular. In the present Chapter climatic conditions at three experimental beech forest sites are described. The territory of Germany extends for about 8° (55°–47°N) from the coastal line of the North and Baltic Seas to the Alps, within the range of maritime temperate climate sub-zones Cfb and Cwb according to Koeppen classification (e.g. McKnight and Hess 2000). It is described as a transition zone between the maritime climate of western Europe and the continental one of eastern Europe. Major agents of the general atmospheric circulation pattern contributing to the maritime character of the climate are the Icelandic low-pressure system, the Azores high-pressure system and often the Asian (or Siberian) high-pressure system. The first two of them furnish western Europe with moisture-loaded air masses propelled by dominant westerly winds. Other major factors are: (1) the maritime influence of the Atlantic Ocean adding to climate ‘oceanicity’; (2) the mountain ranges hindering the southward advance of maritime air masses and, thus, adding to climate ‘continentality’, and (3) the altitude effects in highland regions. Therefore, in general, the oceanicity of climate increases to the north and the west whereas the continentality increases to the south and east. During winter time, the air temperature isotherms run from north to south with values increasing westward, and in summer the isotherms run generally parallel to latitudes (from west to east) with temperatures increasing southward. The mean annual temperature thus decreases generally from north-west to south-east and the annual precipitation from west to east (Fig. 2.1) Table 2.1 summarises the mean climatic conditions over the area of Germany based on data from the German Weather Service (Deutsche Wetterdienst – DWD) for the standard climatological period of 1961–1990. Mean annual air temperature for Germany is +8.4°C with July being the warmest month and January – the coldest. DWD data indicate a gentle increase of annual temperatures after 1988 when compared to the 30-year mean value. Mean annual precipitation for Germany is 700 mm with the pronounced seasonal peak in summer (June–August) with 31.4% of annual precipitation. Seasonal relative minimum value was observed for December–February – 21.5% of annual precipitation. Based on these climatic characteristics most of the land area in Germany could be considered as almost optimal for beech (Fagus silvatica L.) growth as beech prefers oceanic climates with at least 600 mm per year precipitation, with annual mean temperature of about +8° (though wide temperature variations are tolerated) and a growing season of at least 5 months (Mayer 1992). The climatic conditions in Germany fall around these mean values and are classified into four major climatic regions (Schüepp and Schirmer 1977), namely: (1) Northern Lowlands, (2) German Highlands, (3) The German Alpine Foreland and (4) The German Alps. Since the investigated sites are located within the German Highlands, a brief description of climatic conditions of this area is provided below.