In certain regions where mixed farming prevails, the specialization of the farms (with the progressive disappearance of livestock) has brought about uniform methods of land occupation which run counter the environmental functions of farming. For that matter, grasslands and perennial covers have beneficial effects, but their insertion or their maintenance have to be thought out at the territorial scale. The environmental effects of grasslands and perennial forages are described (on soil quality, on the flows of substances such as nitrate and pesticides, on biodiversity, on the landscape, etc.). The area of these perennial covers is of importance, but the way they are inserted spatially in the territory has also to be considered. In certain regions these perennial covers can only be maintained through a voluntary policy of maintenance of livestock on the territories' farms. The association between the rearing of herbivorous stock consuming as much as possible locally produced herbage and the production of cash crops remains basic for a sustainable territorial development and implies the setting-up of new organizations among farms at the local level.