Alternatively, the country may follow and adapt other ecosystem categories used internationally, such as the Millennium Ecosystem Assessment reporting categories. The broadest reporting categories used in the Millennium Ecosystem Assessment32 are forest, cultivated, dryland, coastal, marine, urban, polar, inland water, island and mountain. As recognized by the Millennium Ecosystem Assessment, these ecosystem reporting categories can and do overlap, so countries may wish to decide as to the exact composition, inclusions and exclusions of the main ecosystems in accordance with national or existing international definitions. Ecosystem categories are complicated to describe because of considerations of scale. Ecosystems may be grouped alternatively into biomes, biogeographical regions, habitats or river basins/sub-basins. A biome is a distinct community of plants, animals or fungi that occupy a distinct region.