The observed climatic changes perform very variously, because not only long term trends, fluctuations, short-term anomalies and extreme events are overlaying, but also significant regional and seasonal characteristics occur. These characteristics can be attributed to the geographical location, orographic effects and the region-specific changes of weather patterns. So, for example the climatic diagnosis for Saxony (1951-2000, Franke et al. 2004) shows contrary trends within Saxony, but also varying and contrary trends between the seasons. Similar climatic trends can be caused by completely different weather processes. For the evaluation of impacts of climate change on land use, climatic projctions have to be sufficiently differentiated with respect to temporal (extreme events) and spatial (local) resolution. Hereby, great uncertainty is related to the prediction of precipitation, which is particularly important for plant production. The range of uncertainties has to be taken in account when analyzing the effects on land use.
Regarding the impacts of climate change on agricultural production, positive as well as negative effects are possible, depending on regional climate trends, natural resources of the region and the socio-economic conditions. For example, in case of grassland, higher fluctuations of production may occur, whereby in sub-montane locations higher yields are possible (Fuhrer et al. 1997). Largest losses are expected on intensively used farmland, which however could be overcompensated by the change of varieties and technical progress (Flückiger & Rieder 1997). A comprehensive evaluation of the status about the effect of climate change on German agriculture and forestry has been conducted in the nineties (Enquete-Kommission 1994; Weigel & Kriebitzsch 1995) and has been actualised recently (Schaller & Weigel 2008). However, current concepts of agricultural practice and planning do not include the aspects of climate change, because the local impacts are not quantified.
Deficits of our current knowledge are related to the fact that the existing simulations of agricultural systems are based on future climate projections but today’s types of land use. However, realistic estimates are required, how negative effects can be avoided by changing the type of cultivation, the selection of other varieties and the use of innovative production technologies. So far, not all relevant physiological and ecological processes are represented in the models. For example, increased atmospheric CO2 concentrations affect vegetation directly by stimulating plant growth and influencing the water regime and surface temperatures of plant canopies via feedback effects. Direction and dimension of model-based predictions of the effects of changing temperatures and precipitation on agricultural plant production and the element as well as water fluxes in agricultural ecosystems are significantly determined by the fact, whether and in which order of magnitude the physiological CO2 effect is considered. For a realistic estimate of production losses and the following consequence of measures (irrigation, development of varieties), improved knowledge at stand level and of the respective site conditions of cultivation are necessary (Weigel & Dämmgen 2000).
Effects of climate change on plant production and land use can not be studied without considering the landscape system if the ecological sustainability of measures, i.e. the maintenance of ecosystem services shall be provided. Changes of evaporation, land-surface temperatures and land use can have effects on climatic conditions at the landscape scale. The uptake and release of greenhouse gases depend on management practices at the field scale are influencing the greenhouse effect at the global level. Hereby, agriculture has to be taken into account under the viewpoint of climate protection. Besides the areas of intensive agriculture, the semi-natural vegetation (wood, grassland) plays a major role for mitigation (carbon sink) as well as for the indication of climate change (phenology, indicator plants). To make these functions applicable as a basis for adaptation measures, again better estimates are required for example, to evaluate how the positive effects of a longer growing season may be outcompeted by an increase of extreme events. Whether and how the predicted shifts of vegetation zones will become apparent in the cultural landscape is not known up to now. The improved availability of climate data with high spatial and temporal resolution will help to identify climate related changes of the potential plant production.
From the socio-economic viewpoint, the agricultural enterprises, their upstream and downstream economic sectors as well as political decision-makers are, with different focus, interested in estimates of possible impacts caused by an upcoming climate change. For example, for agricultural companies the future climate conditions and individual possibilities of adaption at their respective production locations are of great significance for their investments.
Plant breeding companies consider future production conditions in agriculture when they are formulating their long-term breeding objectives to provide in time appropriate products adapted to changing requirements on cultivated plants and varieties. To develop new insurance products, insurance companies need information on potential damages caused by climatic extremes on larger spatial scales. For political decision makers information about the regional and local impacts of climate change on agriculture is important to support the process of adaptation by purposeful measures contributing to sustainable development of rural areas.
Therefore, the development and evaluation of adaptation strategies requires to jointly consider ecological and socio-economical interrelations. The results of an integrated analysis and evaluation are of great significance for decisions by different actors on the global, regional and local scale.
Literatur
Enquete-Kommission „Schutz der Erdatmosphäre“ des Deutschen Bundestages (Hrsg) (1994): Schutz der grünen Erde: Klimaschutz durch umweltgerechte Landwirtschaft und Erhalt der Wälder. Economica, Bonn.
Flückiger S, Rieder P. (1997): Klimaänderung und Landwirtschaft. Schlussbericht NFP 31, vdf Hochschulverlag AG, ETH Zürich, 222 S.
Franke J, Goldberg V, Eichelmann U, Freydank E, Bernhofer Ch (2004): Statistical analysis of regional climate trends in Saxony, Germany. Clim Res 27, 145-150
Fuhrer J (Hrsg) (1997): Klimaänderung und Grünland. Schlussbericht NFP 31, vdf Hochschulverlag AG, ETH Zürich, 307 S.
Schaller M, Weigel H-J (2008): Analyse des Sachstandes zu Auswirkungen von Klimaveränderungen auf die deutsche Landwirtschaft und Maßnahmen zur Anpassung.. Landbauforschung Völkenrode, Sonderheft 316
Weigel HJ, Kriebitzsch WU (1995): Wirkungen von Klimaänderungen auf Agrar- und Forstökosysteme. In: Klimawirkungsforschung im Geschäftsbereich des BML. Schriftenreihe des BML, Reihe A: Angewandte Wissenschaft, Heft 442, 43-59
Weigel HJ, Dämmgen U (2000): The Braunschweig Carbon Project: Atmospheric Flux Monitoring and Free Air Carbon Dioxide Enrichment (FACE). Journal of Applied Botany 74, 55-60
