Old-growth grasslands are ancient ecosystems characterized by high herbaceous species richness, high endemism, and unique species compositions. On the other hand, anthropogenic grasslands, although more recent, cannot be limited to species poor planted pastures. Among anthropogenic grasslands can be found: (i) recent anthropogenic grasslands, such as planted pastures and (ii) species-rich anthropogenic grasslands, traditionally managed using mowing, grazing and/or fire. With the development of carbon payment scheme, grassy biomes are targeted by tree planting. While it may be appropriate to plant trees on low diversity pasture that were previously forested (reforestation: planting trees on deforested land or agroforestry), planting trees on old-growth grasslands or on species-rich anthropogenic grasslands is done at a high environmental cost. The purpose of this talk is to show how species-rich anthropogenic grasslands are being dealt with. In Europe, it is recognized since the 1990’s that most of these grasslands can lose diversity and characteristic species if management stops and thus if secondary succession occurs. While, tree planting on such systems most likely leads to the same result, afforestation is increasing due to the increasing demand for timber and wood products and the abandonment of agricultural land. In Madagascar, both old-growth and anthropogenic grasslands are currently present: anthropogenic grasslands dominate highland areas and have been maintained by human driven fire regime and grazing. The synergy between (i) the mistaken idea that all these grasslands have low conservation values and (ii) the need to cover the human needs in fuelwood has resulted in extensive areas being planted with exotic trees (e.g. Pinus, Eucalyptus and Acacia species) which colonize outside of planted areas and are a major management problem. Overall, the implications of afforestation for biodiversity depend on the land-use and conservation values prior to tree planting and on the way afforestation is carried out.