Guyana abounds with plant and animal life. Each region boasts unique species. The following habitats have been categorized for Guyana: coastal, marine, littoral, estuarine palustrine, mangrove, riverine, lacustrine, swamp, savannah, white sand forest, brown sand forest, montane, cloud forest, moist lowland and dry evergreen scrub forests (NBAP, 1999). About 14 areas of biological interest have been identified as possible hotspots for a National Protected Area System. More than 80% of Guyana is still covered by forests, ranging from dry evergreen and seasonal forests to montane and lowland evergreen rain forests. These forests are home to more than a thousand species of trees. Guyana's tropical climate, unique geology, and relatively pristine ecosystems support extensive areas of species-rich rain forests and natural habitats with high levels of endemism. Approximately eight thousand species of plants occur in Guyana, half of which are found nowhere else. Guyana is one of the countries with the highest biodiversity in the world. Guyana, with 1,168 vertebrate species, 1600 bird species, boasts one of the richest mammalian fauna assemblages of any comparably sized area in the world. The Guiana Shield region is little known and extremely rich biologically. Unlike other areas of South America, over 70% of the natural habitat remains pristine. The rich natural history of British Guiana was described by early explorers Sir Walter Raleigh and Charles Waterton and later by naturalists Sir David Attenborough and Gerald Durrell.