Changing forests, changing ecosystem services. Example in Vietnam
Résumé
Like other countries in Asia, Vietnam knew a decline of its forests during the XXth century. The war is often mentioned as an original driver, above all due to herbicides spraying by the American army. But the analysis of remote sensing data (aerial photographs and satellite images) reveals an acceleration of the forest decline after the war: forest exploitation and progression of the sedentary agriculture are the main reasons. The underlying causes are population growth, the sedentarization of minority ethnic groups and the migration of the majority ethnic group, mostly organized, to create new economic areas. Forests have been gradually replaced by cultivated land and savannahs. This landscape dynamic has led to an erosion of biodiversity, changes in soil properties, climate changes...: all biophysical parameters were affected. Since the 1990s, a new dynamic has been initiated: the forest area is increasing but it is no longer the same forests. Vietnam has launched a vast reforestation program. Acacia plantations are replacing savannahs over large areas. Without being comparable to spontaneous forests, these new “forests” offer ecosystem services, first of all provisioning services. They can also contribute to climate change mitigation, restore the nitrogen content of the soil. However, they are more fragile in the face of fires and insect outbreaks, which will increase with climate change, and the possibility of cultural services remains to be questioned. The presentation will thus be an opportunity to question the evolution of ecosystem services in relation to the dynamics affecting forests, given that current services are also influenced by past services.