The northern tarai region (also called terai) of Nepal was densely forested and sparsely populated until the malaria eradication programme took effect in the 1960s. Since then, much of it has gradually been cleared and converted into agricultural land for the resettlement of the hill population. The harvesting of extremely high-value sal (Shorea robusta spp) forests for revenue has also been a major factor in the deforestation. There has been no systematic management of forests, and timber mafias conduct large-scale operations in the tarai.