The rubber tree is native to the humid tropics and has traditionally been cropped in the equatorial zone between 10°N and 10°S; in mainland Southeast Asia this includes portions of southern Thailand, southeastern Vietnam, and southern Myanmar. In the early 1950s, the Chinese government began to invest in growing rubber in environments perceived to be ecologically marginal and eventually established state rubber plantations in areas that lie as far north as 22° north latitude. China's success in growing rubber in these ‘non-traditional’ environments expanded the habitat in which rubber could be planted and pushed it further north. Today entrepreneurs from China, Vietnam, Malaysia, and Thailand are investing in rubber plantations in areas of Laos, Cambodia, and Myanmar, northwest Vietnam, northeast Thailand, and Yunnan, China. The impact of rubber on smallholders, however, is not yet clear. Experiences in Xishuangbanna, Yunnan, China and northeast Thailand clearly show that smallholder rubber production is a viable and effective proposition in moving households and communities out of poverty. By contrast in countries such as Laos, Cambodia and Myanmar many farmers are struggling to maintain their lands and forests in the face of growing pressures from investors and government institutions to impose concession arrangements.

In Vietnam, the remarkable economic growth that resulted from the doi moi (renovation) reforms was based largely on the rural households that had become the new basic unit of agricultural production in the early 1990s. The technical, economic, and social changes that accompanied the decollectivization process transformed agricultural production, resource management, land use, and the institutions that defined access to resources and their distribution. Combined with the extreme biophysical, technical, and social heterogeneity encountered in the northern mountains, these rapid changes led to the extreme complexity of the agrarian dynamics that today challenges traditional diagnostic approaches. Since 1999, a participatory simulation method has been developed to disentangle the cause-and-effect relationships between the different driving forces and changes in land use observed at different scales. Several tools were combined to understand the interactions between human and natural systems, including a narrative conceptual model, an agent-based spatial computational model (ABM), a role-playing game, and a multiscale geographic information system (GIS). We synthesized into an ABM named SAMBA-GIS the knowledge generated from the above tools applied to a representative sample of research sites. The model takes explicitly into account the dynamic interactions among: (1) farmers' strategies, i.e., the individual decision-making process as a function of the farm's resource profile; (2) the institutions that define resource access and usage; and (3) changes in the biophysical and socioeconomic environment. The next step consisted of coupling the ABM with the GIS to extrapolate the application of local management rules to a whole landscape. Simulations are initialized using the layers of the GIS, e.g., land use in 1990, accessibility, soil characteristics, etc., and statistics available at the village level, e.g., population, ethnicity, livestock, etc. At each annual time step, the agrarian landscape changes according to the decisions made by agent-farmers about how to allocate resources such as labor force, capital, and land to different productive activities, e.g., crops, livestock, gathering of forest products, off-farm activities. The participatory simulations based on SAMBA-GIS helped identify villages with similar land-use change trajectories to which the same types of technical and/or institutional innovations could be applied. Scenarios of land-use changes were developed with local stakeholders to assess the potential impact of these changes on the natural resource base and on agricultural development. This adaptive approach was gradually refined through interactions between researchers and the local population