Congolese forests cover some 22 million hectares (54.3 million acres), or 65% of the total land area of the country. There are three main zones. Mayombé forest, covering about one million hectares (2.5 million acres), is the oldest forest under commercial exploitation and is almost exhausted. The Niari forest, covering three million hectares (7.4 million acres), along the Chaillu River, was reopened for exploitation after completion of the Comilog railroad. The third zone, situated in the north, is the largest, with 15.5 million hectares (38.3 million acres); because of constant flooding, however, it is the least exploited. Total production of roundwood was 1.8 million cu m (63 million cu ft) in 2000; exports of roundwood were valued at $76 million. Okoumé, sapele, sipo, tiama, moaki, limba, and nioré were the main species cut. Eucalyptus and pine are raised commercially in southern and coastal Congo. Foreign private companies dominate commercial production. The Congolese Forestry Office was set up in 1974 to implement an ambitious reforestation program. Forestry contributes only 3% to GDP, and development was neglected during the oil boom years. Forest products contribute over 5% to the value of all exports. Isolated harvestable tracts, difficult weather conditions, and limited rail transport capacity inhibit the expansion of the forestry sector.