Iceland consists of eight geographical regions, Capital Region, Southern Peninsula, West, Westfjords, Northwest, Northeast, East and South. Twenty percent of the land is used for grazing, while only one percent is cultivated. Iceland has lost most of the woodland that previously covered large areas of the country, but an ambitious reforestation program is currently underway. Fossilized tree pollen and descriptions by the early settlers indicate that prior to human settlement, now thought to have occurred from around AD 800 onwards, trees covered between thirty and forty per cent of the island. Today, however, there are only small patches of the original birch forests left, the most prominent being Hallormsstaðaskógur and Vaglaskógur. The country of Iceland contains 36 islands. The longest river on the island is Þjórsá at 230 kilometres (about 143 miles). Iceland has three national parks: Vatnajökull National Park, Snæfellsjökull National Park, and Þingvellir National Park. The inhabited areas are on the coast, particularly in the southwest, while the central highlands are all but uninhabited. The island's terrain is mostly plateau interspersed with mountain peaks, icefields and a coast deeply indented by bays and fjords.