Land use changes have been investigated as well as their impact on landscape evolution diversity of production systems in the mountainous province of Bac Kan, Vietnam. In-depth surveys were conducted in 1999 and 2000 with farmers and local development stakeholders in order to assess the role of socioeconomic transformations as driving force of land use changes. The historical pathway begins in the 1950s with a dual agricultural system based on differentiated access of two main ethnic groups (Tay and Dao) to the two main landscape units (lowlands and uplands) respectively. The main crop is irrigated rice in the former system and shifting cultivation of upland rice, maize and cassava in the latter. Then, collectivization, associated to introduction of the green revolution innovations, allowed intensification of the lowland where all agricultural activities were concentrated. The forest could regenerate on the slopes until the malfunctioning of cooperatives led more and more hungry farmers to exploit it through shifting cultivation again. Between 1980 and 1995, a stepwise economical liberalization process led some farmers to intensify the rice cultivation in the lowland, whereas other groups relied mainly on the mining exploitation of natural resources to develop their new household economy. A farming system differentiation model had been proposed for this period of intensive environmental degradation, which is based on the ratio household labour force/number of mouths to feed" up to the early 1990s, then on modalities of the lowland allocation process. It explains the current farming system diversity in the light of recent economic and institutional transformations: distribution of production means to farmers; land entitlement; and new governance systems. The interpretation of a chronological series of aerial pictures from 1954, 1977 and 1998 shows a tremendous impact of land use changes on ecological dynamics, especially on deforestation. However, one can now observe through field surveys a reserve trend a relative forest recovery thanks to the recent forest land allocation to households and governmental reforestation programmes. But this trend is not yet perceptible on the latest land use maps. Finally, the analysis of farming systems strategies in a highly dynamic biophysical and socioeconomic environment was used to better target the interventions of development agencies and national extension services working in the area. Viable alternatives to slash and burn practices have to be developed rapidly and proposed to the numerous farmers who rely exclusively on the uplands. Even though the ecological and economic benefit of these new techniques is proved, they will need to be accompanied with relevant organizational innovations to secure a large adoption among highlanders. Beyond the understanding of past changes, the purpose of this diagnostic study is to better target with relevant innovations the different farmer's types identified during the on-farm survey."
