SBR- Content.pmd - INBO

State of the Basin Report - 2003The environmental implications of shiftingcultivation depend upon the intensity withwhich it is practised and upon the nature ofthe land in question. The key to whether thepractice is environmentally sustainable is thelength of the fallow period, which itselfdepends upon population density. 76 Thecarrying capacity of land under shiftingcultivation is estimated to be 20-40 personsper km 2 . In the northeast of Cambodia, forexample, population density is less than 20people per km 2 , and shifting agriculture,Shifting cultivators are primarily from ethnic minoritiesalthough prevalent, is not considered to be amajor environmental problem. 77 Population densities in this range allow for the required fallowperiods of 10-20 years, but if there are more people in an area, land scarcity forces shorter periods,often as low as 5-7 years. Such periods do not allow for full regeneration of soil fertility, nor do theyallow trees to grow tall enough to overshadow and kill off invading plants and weeds. 78 Otherconsequences of excessively short fallow periods include increased erosion due to the reducedcapacity of the soil to retain water. Sloping lands are particularly vulnerable to developing erosionproblems when fallow periods become too short. When such areas are near river tributaries, erosionmay increase the load of silt washing into rivers.Increasingly, the carrying capacity of shiftingcultivation land is being exceeded because ofpopulation growth, government sponsored orindependent in-migration, and decreasing landavailability due to hydro-power schemes,reclassification of forests as protected areasand the granting of logging concessions. 79 Theinsecure land tenure arrangements prevalentacross the basin also contribute to the problemby making it easier for the land of shiftingcultivators to be expropriated, which givesthem less incentive to ensure its environmentalEthnic minority Thai Luu plant red corn for cattle feedpreservation. 80 Such changes can start anoften-observed cycle whereby increased land pressure leads to shortened fallow periods, which inturn cause a loss of soil fertility and declining crop yields, as well as increased erosion, downstreamsiltation, flooding and drought, all of which increase human poverty and vulnerability. 81Shifting cultivation is most significant as an environmental and social problem in Lao PDR.Government figures indicate that between 1982 and 1989, over 300,000 ha were cleared and plantedfor shifting cultivation by an estimated 280,000 families. 82 In the 1990s, government programmesto resettle upland residents and provide them with alternative livelihoods helped stabilise the practice.By 1995, the area decreased to 192,258 ha with 198,868 households and by 1998 to 148,000 hawith 156,720 households. However, most of the rehabilitated area was in the sloping landssurrounding the Mekong Corridor, while shifting cultivation continued unabated in the remoterupland areas. 83 It is estimated that 70 percent of northern households practice shifting cultivation,compared to only 12 percent for the flatter southern region. 84 There are two main types of shiftingcultivation based on ethnic minority practices. The Khmu in the midlands traditionally practicerotational cultivation, while the Hmong and other highland groups have more commonly practicedthe pioneering variant, with frequent moves to virgin areas.166