Forest Guardians, Forest Destroyers: The Politics of Environmental Knowledge in Northern Thailand

6. Erosion

6 Erosion Many of thailand’s narratives about forests and water are intricately connected to beliefs about soil erosion. Visitors to the uplands are often struck by how farming seems to cling to steep slopes, and how villages perch precariously on narrow ridges. Popular notions of soil erosion suggest careless agriculture will wash soil downhill, where it is then deposited on roads, on rice fields, and in irrigation channels. And erosion on the hillsides is believed to reduce agricultural productivity and diminish the water-holding properties in upland soils. According to one United Nations report in 1988, there is now ample evidence of degradation and erosion of soils in Thailand. Changes in physical and chemical properties of soils have made many more susceptible to erosion and it is now estimated that about 107 million rai [18 million hectares] nationwide suffer from a medium to high degree of soil erosion, particularly in upland areas where slopes are greater than 5 percent. . . . The eroded topsoil, itself, of course, causes further problems downstream. (unep 1988:6–7) And the conservationist ngo, the Dhammanaat Foundation, that was influential in the Chom Thong dispute, argued that “heavy rains wash away the soil, which quickly silts up dams, reservoirs and rivers. . . . Every rainy season now, lowland paddies are buried under 2–3 meters of sand. . . . The evergreen headwater forest should be areas of strict conservation as their removal brings about environmental disaster” (Svasti 1998). 139 As a result of these concerns, various development programs, government initiatives, and scientific research projects have focused on soil conservation. The Land Development Department (2004) reiterated the relationship between environmental “crisis” and statemaking by describing soil erosion as an issue of national importance and proposing a wide array of regulatory interventions to manage it. One of the most common approaches is to limit cultivation on vulnerable hillslopes (figure 6.1 shows a steep slope under cultivation), often by replacing smallholder agriculture with pine or teak plantations. In the 1970s, the Land Development Department adopted a policy that stated that “soils that are either too steep . . . or that are too gravelly or stony . . . or that are too shallow . . . for cultivation of most upland crops . . . can be best used for timber production ” (Scholten and Wichai 1973:89). In many upland areas where commercial reforestation is not possible, farmers have been encouraged to plant fruit trees. Grass “filter strips” have also been widely promoted as a means of reducing soil erosion on upland slopes. The Royal Forest Department’s watershed management units are reported to have distributed over forty million vetiver grass seedlings between 1993 and 2000 (rfd 2004e). And various government agencies have also encouraged the terracing of sloping land or the development of paddy fields in lowslope valley bottoms. These various interventions in upland landscapes and livelihoods are seen as crucial in maintaining upland soil quality, reducing downstream impacts, and avoiding the need for further deforestation in search of undegraded soils. But these common cause-and-effect statements about soil erosion are not always confirmed by research findings. Moreover, some of the proposed solutions to problems of soil degradation may not necessarily address complex issues of soil management. There is a need to look more closely at common beliefs about erosion and sedimentation in Thailand and to assess how far popular conceptions have been “stabilized” by social and political factors. popular conceptions of erosion Soil erosion is the removal of soil by wind or water. It is an important cause of declining agricultural fertility because erosion removes soil nutrients , or the soil particles that hold nutrients and moisture. By and large, wind erosion is not a common problem in Thailand. Water erosion, however , can occur in a variety of ways. Sheet erosion is the removal of soil 140 Erosion across the surface of the land, while gully erosion involves the development of deep trenches. Rills, or rivulets, are smaller indentations that can occur simultaneously with sheet erosion or that can lead to the formation of gullies.1 Under intense rainfall the overland flow along rills and gullies can resemble temporary streams. Tillage on agricultural land can contribute to erosion by making the soil easier to wash away, and can also be a source of erosion in itself as the action of digging on sloping land gradually moves the soil downslope (Turkelboom et al. 1999). River erosion can also contribute to riverbank soil loss. Erosion is an everyday...