An estimated 31% of Liberia is covered by forest, its use largely confined to production of lumber for local needs. National forests constitute about 18% of the land area. In 2000, Liberia had 119,000 ha (294,000 acres) of forest plantations. There were five major reforestation areas with a total of 4,260 ha (10,500 acres). About 235 timber species grow in Liberia, of which 90 are potentially marketable, but natural stands of a single species are not common. This fact, plus difficulty of access and lack of practicable means of transportation, has tended to discourage commercial logging operations, despite the known existence of such valuable woods as African mahoganies and red ironwood. A number of foreign companies, mainly from the United States, have been granted concessions. The timber cut in 2000 yielded 5,062,000 cu m (178.7 million cu ft) of roundwood, of which 95% was burned as fuel. Roundwood exports in 2000 totaled 637,000 cu m (22.5 million cu ft) and were valued at $67.5 million.