2009 年 18 巻 3 号 p. 155-166
Intensification of farmers’ land use with perennial crops is expected to prevent the destruction of forests caused by their extensive slash-and-burn cultivation in the tropics. However, effects of tree crops on natural forests are controversial, affected by various socio-economic factors. This article discusses impacts of farmers’ crop cultivation on natural forest conversion by examining a case study from West Sumatra, Indonesia. Sample farmers cultivated lowland paddy fields and upland non-paddy fields. They cleared natural forests merely to grow perennial cash crops such as coffee, rubber, and cinnamon, some of whom may have migrated to forest areas. Coffee was productive in assarted plots that sample farmers originally converted from natural forests, as preferring pristine soils. Rubber and cinnamon occurred commonly in plots outside forests that other farmers already cultivated and transferred to sample farmers with considerable profits, though planted on assarted plots as well. Single or mixed cultivation of these tree crops was not yet optimal, incurring land degradation at times. Some farmers grew profitable but laborious non-rice food crops on small lowland fields by converting insufficient paddy fields, encouraged by good markets. Their concentration on lowland farming alleviated destruction of upland natural forests noticeably. Farmers utilized profits from surplus rice harvests to expand tree crop cultivation in upland forest areas for future income, while substituting non-rice food crops for lowland rice for their subsistence. Perennial cash crops generally aggravate farmers’ forest clearance rather than commercial non-rice food crops grown intensively outside forests. However, impacts of different tree crops vary on forest conversion. Fast-growing pioneer tree crops like coffee bring about more extensive conversion than slow-growing follow-up tree crops like rubber or cinnamon which can be grown in any land conditions. Forest clearance for tree planting could be alleviated by intensifying farmers’ land use outside forests through flexible combination of tree crops and food crops adaptive to various land conditions, provided substantial crop profits and equitable land allocation.
