The purpose of the NVC is to provide a complete, standardized listing and description of all vegetation types that represent the variation in biological diversity at the community level and to identify those communities that require protection. The NVC focuses on existing vegetation rather than potential natural vegetation, climax vegetation, or physical habitats. Because it is not restricted to static vegetation types, classification units are useful both for inventory, site description, and as the basis for building dynamic ecological models. The NVC also includes vegetation along the natural-invasive-cultural (semi-natural and modified) continuum, but it emphasizes natural communities as the focus of biodiversity protection.