Des indicateurs d'évolution du milieu et des sols pour rendre durable l'usage des savanes d'Amérique du Sud

Abstract

South American savannas cover some 2.69 million sq km across Brazil, Colombia, Venezuela and Bolivia. On a world-wide scale they represent one of the most extensive land areas with agricultural potential for crop and forestry production. Besides, these vast stretches of land are also the main alternative for avoiding the extension of agriculture to fragile tropical areas of higher ecological risk, such as the tropical rain forests and hillsides. Over the past four decades introduced pastures consisting chiefly of African species, in particular from the genus Brachiaria and Andropogon, and cropland have replaced the natural vegetation having low nutrient requirement in the savannas (Llanos) of Colombia and Venezuela, as well as in the Cerrado (Brazil). Intensive reforestation schemes have also taken place with alien species such as Pinus and Eucalyptus for pulpwood and timber production. The introduction of African grassland species and annual and perennial crops were made possible through the use of intensive fertilization, particularly with inorganic amendments. Following a preliminary comparative review of the colonization process by agriculture in the Llanos and Cerrado and a survey of some soil biogeochemical features, we show the crucial relation between these environments and current environmental stakes and the need to generate new indicators for the use of savanna areas. © NSS Dialogues, EDP Sciences 2005.