To prepare agriculture and forestry for the climatic change forecast for the twenty-first century, particular efforts must be made in research, based on the knowledge on climate data currently available, for the development of the most up to date applied management techniques. This development must be accompanied by efforts in agronomic research which take climatic change into account for research in plant genetic improvement and development of sustainable cropping systems to attain operational applications for adaptation strategies. It then becomes indispensable to single out two ways of adaptation depending on the final user: those which can be implemented by the farmer (for example modification of sowing dates, varietal choice or use of seasonal forecasts) and those of decision-makers (e.g. land and natural resource managers) which necessitate investment in infrastructures (particularly water resource projects). Thus, in operational terms, the results of research will have to contribute to the implementation of durable construction and management options which enable the adaptation of agrosystems and forest ecosystems to climate change. This will include identification of sensitive areas, choice of new crops, understanding mechanism of species replacement, calculation of future water needs and collection, visualisation of geographical species area and potential changes in impact of pests and diseases.

To the scientific and technical problems raised by adapting agriculture and forestry to climatic variability and change must also be added socio-economic considerations which will not be covered in this article but which will have to be borne in mind. Hence, any significant modification in local production will necessarily affect the global organisation of markets and economic and social systems. Conversely, agriculture and forestry are likely to make a significant contribution to climatic change dynamics through the emission of greenhouse gases (GHG) or, on the contrary, the storage of CO2. The combination of these elements will be analysed in the text below, supported equally by climatic research in relation to agricultural and forestry production issues.

Our arguments will rely principally upon examples relating to France, a temperate region, but we have tried to extend their scope by broadening our considerations to semi-arid and tropical zones. In these areas, the precariousness of ecological and social systems combined with the impact of climate change is likely to have a major effect on the productivity and balance of cultivated ecosystems (reduction of biodiversity due to an increased drought, irreversible erosion of land linked to flooding). This may lead in some cases to the migration of human populations if food safety is affected. Indeed, even though the simulations show a higher elevation of temperature in polar and temperate latitudes, in relation to the tropical latitudes, tropical crops are today much closer to their thermal optimum and hence more likely to suffer from thermal excesses in the future. Insects and diseases, already very active in tropical zones, could proliferate and widen their area of influence. The combination of these factors, to which must be added the dependence of less developed countries on agriculture and its risks stress, the fragility of economic and social conditions. This makes a number of tropical regions risk areas likely to suffer the implicit negative effects linked to climatic change (Rosenzweig and Hillel, 1978).

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