Natural communities change over time, as does the scientific understanding of those communities. Sometimes important distinctions are discovered within a natural community. When these distinctions are notable enough, two natural communities, rather than one, are then recognized. In such cases, a new name is added to the National Vegetation Classification (NVC).
In other cases, the opposite may be true: distinctions between two natural communities are discovered to be less important as more information is collected, and the two natural communities are lumped together under one name.