The island of Saint Helena has a total area of 122 km2 (47 sq mi), and is composed largely of rugged terrain of volcanic origin (the last volcanic eruptions occurred about 7 million years ago). Coastal areas are covered in volcanic rock and warmer and drier than the centre. The highest point of the island is Diana's Peak at 818 m (2,684 ft). In 1996 it became the island's first national park. Much of the island is covered by New Zealand flax, a legacy of former industry, but there are some original trees augmented by plantations, including those of the Millennium Forest project which was established in 2002 to replant part of the lost Great Wood and is now managed by the Saint Helena National Trust. When the island was discovered, it was covered with unique indigenous vegetation, including a remarkable cabbage tree species. The island's hinterland must have been a dense tropical forest but the coastal areas were probably also quite green. The modern landscape is very different, with widespread bare rock in the lower areas, although inland it is green, mainly due to introduced vegetation. There are no native land mammals, but cattle, cats, dogs, donkeys, goats, mice, rabbits, rats and sheep have been introduced, and native species have been adversely affected as a result. The dramatic change in landscape must be attributed to these introductions. As a result, the string tree (Acalypha rubrinervis) and the St Helena olive (Nesiota elliptica) are now extinct, and many of the other endemic plants are threatened with extinction.