Norfolk Island has 174 native plants; 51 of them are endemic. At least 18 of the endemic species are rare or threatened.23 - The Norfolk Island Palm ( Rhopalostylis baueri ) and the Smooth Tree-fern ( Cyathea brownii ), the tallest tree-fern in the world,23 - are common in the Norfolk Island National Park but rare elsewhere on the island. Before European colonization, most of Norfolk Island was covered with subtropical rain forest, the canopy of which was made of Araucaria heterophylla (Norfolk Island Pine) in exposed areas, and the palm Rhopalostylis baueri and tree ferns Cyathea brownii and C. australis in moister protected areas. The understory was thick with lianas and ferns covered the forest floor. Only one small tract (5 km²) of rainforest remains, which was declared as the Norfolk Island National Park in 1986.23 - This forest has been infested with several introduced plants. The cliffs and steep slopes of Mt Pitt supported a community of shrubs, herbaceous plants, and climbers. A few tracts of clifftop and seashore vegetation have been preserved. The rest of the island has been cleared for pasture and housing. Grazing and introduced weeds currently threaten the native flora, displacing it in some areas. In fact, there are more weed species than native species on Norfolk Island.23 -