Steps and Methods for the Identification of Potential Land-Use Units

Steps and Methods for the Identification of Potential Land-Use Units In the San Patong Land Reform Area, Chiang Mai Province, Northern Thailand Dr. Harald Kirsch1, German Development Service (DED), Phnom Penh Abstract Within a joint project carried out by three academic institutions from Germany, Netherlands and Thailand in 1992 - 1995 potential land-use units were defined for a land reform area in Northern Thailand. After a stepwise integration of physical and socio-economic data all land use potentials and constrains were analysed to explain land use changes occurred during the project period, and to sug- gest potential future types of land utilization. Besides economical constrains, the soil quality and access to water proved to be the main factors. Since the physical conditions defining the land suitability in the study area are very similar to the flat to slightly undulating lowland areas of Cambodia, conclusions for a process leading from land resource assessment (LRA) to a land suitability evaluation in this country can be drawn. Land suitability evaluation is supposed to support Participatory Land Use Planning (PLUP) in Cambodia. This paper summarizes the content and main points of the corresponding presentation given by the author during the LRA Forum in Phnom Penh, Cambodia in Sept. 20042. 1. Introduction The project reported here, with the title Improvement of Crop Yields and Simultaneous Environ- mental Impact Assessment in Conjunction with Intensification and Diversification of Agroforestry on Marginal Land in Northern Thailand was carried out between May 1992 and April 1995. It was supported by the European Commission under the program "Life Sciences and Technologies for De- veloping Countries #3 (STD3). The project's main objectives were (RAKARIYATHAM & KIRSCH 1995): Improvement of crop yields by analyzing their key parameters together with an inventory of natural resources, followed by a classification of potential land-use units. Assessment of the impact of agricultural land-use on the environment. Assessment of the sustainability of agroforestry on marginal land. Training of Thai scientists in the fields of ecological research and GIS. Improving agricultural technology and making it available to the farmers. Providing data as a base for further development. Institutions from three countries were involved in the project. These were: Institute for Physical Geography, Frankfurt University, Germany ITC Enschede, The Netherlands Dept. of Geography, Faculty of Social Sciences, Chiang Mai University; Dept. of Sociology and Political Science, Faculty of Social Sciences, Chiang Mai University Dept. of Chemistry, Faculty of Science, Chiang Mai University Multiple Cropping Centre, Faculty of Agriculture, Chiang Mai University 1 Dr. Harald Kirsch, PLUP Adviser, c/o DED, P.O. Box 628, Phnom Penh, Cambodia; [email protected] 2 BELL et al. (2006) Harald Kirsch: Steps and Methods for the Identification of Potential Land-Use Units The Dept. of Geography of Chiang Mai University (CMU) was responsible for the co-ordination and management of the multidisciplinary project, supported by a visiting scientist from Frankfurt University. Students from Chiang Mai and Frankfurt had the chance to do research in the study area for their M.Sc. or Diploma thesis. 2. The study area: location, relief, history and background The project area is located in the upper Mae Nam Ping basin about 35 km southwest of Changwat Chiang Mai, between Amphoe San Patong, Changwat Lamphun, Amphoe Chom Thong and the Doi Inthanon mountain range (fig. 1). It comprises 26 km2, and elevations range from 300 to 370 m above sea level. The relief is in general flat to undulating (photo1), with escarpments separating the upper terrace from the lower lying relief units (photo 2, fig. 2). The area is under the land allo- cation program (Chom Thong Land Reform Area) of the Land Reform Department (LRD); its larg- est part of it is located on the topographical map sheet named Amphoe San Patong. The rain shadow effect of the Doi Inthanon mountain range is quite significant. The average annual precipitation of 690 mm amounts about 60 % of the rainfall in Chiang Mai 35 km to the north. In the study area a very pronounced dry spell occurs in July. Location of the study area (Topographic Map 1:250 000, Sheet NE 47-6, Changwat Chiang Mai) Figure 1: Location of the study area Since 1986 at total number of 2400 plots of land were distributed by LRD to 1960 poor, landless farmers and their families. Most of the farmers (85%) have a plot of 5 rai (8000 m2), while the early settlers who cleared the land received 10 rai (15%). Previously the land was covered by degraded dry deciduous forest and grassland (mainly Dipterocarpus spp. and Imperata cylindrica). The deg- radation was a result of the extension of farmland for soybean and tobacco cultivation, but also of extensive firewood and charcoal production since 1952. 2 Harald Kirsch: Steps and Methods for the Identification of Potential Land-Use Units The land reform program is supported by the Multiple Cropping Centre (MCC) of Chiang Mai Uni- versity in the fields of crop research, extension and technical advisory service. MCC is also running a test and demonstration plot in the LRD area Figure 2: Overview map of the major relief units of the upper Ping Basin Photo1: Gently sloping relief of the project area Photo 2: Edge of the upper terrace 3. Basic data: collection, processing and presentation The data sources used were field survey results, aerial photos, satellite images, and topographical maps of various scales. Additional information came from laboratory analysis of soil and water samples, socio-economic studies conducted by students of CMU, and participation of local farmers. All field data and mapped information were processed with the GIS ILWIS, provided by ITC Enschede. These were the major steps: 3 Harald Kirsch: Steps and Methods for the Identification of Potential Land-Use Units To get an overview on the landscape and its characteristics, the relief units of the upper Mae Ping basin were classified according to interpretation of aerial photographs (1:50 000). A draft was made with the topographical map (1:250 000) as a base map, and then digitized. Through field survey it was found that the flood plain / lower terrace, middle terrace and upper terrace (photo 2) as well as the eastern part of the hilly and mountainous area are composed of loose Pleistocene sediments. Tectonic uplift and lowering, and related sedimentation and de- nudation caused the different relief units and elevation levels (fig. 2 & 43). A LandSat 5 TM interpretation provided information on different ground cover and moisture conditions in the study area and its surrounding landscape. Based on a topographical map (1:10 000) with 1-meter contour interval (provided by the LRD) elevation and slope maps were produced. Elevations range from 305 m on the lower terrace to 368 m in the hills. About 80% oft the area has a level to gently sloping (undulating) relief with a slope of 0 – 3.5% (photo1). Zones of geomorphological structures (faults and joints, drainage systems, escarpments) were identified by interpretation of aerial photographs (1:15 000), then transferred on the base map (topo map 1:10 000) and later digitized (fig. 4). Land use and vegetation data were collected by ground survey conducted by Geography students of CMU in 1992 and 1994. The surveys showed that the number of fallow land plots and orchards increased during that period, while the number of plots with annual crops declined (fig. 5). Geologically the whole project area is build up by 4 types of loose sediments. Point data gained from field survey (ca. 70 soil survey sites) were extrapolated and then correlated with relief units and land use. In more than 70% of the area the pinkish white sand forms the topsoil. Five different soil profile types could be distinguished according to the sequence of the geological material (fig. 3). Figure 3: The five major soil profile types of the study area distinguished according to geology and strati- graphic sequences (CL1: pinkish white sandy layer, CL2: orange/red clayey layer, GR: gravel layer in sandy clayey matrix, Other material (hillwash or suspended load). It was found that the 5 major profile types form different soil types - mainly varieties of Alisols, Ac- risols, Plinthosols and Arenosols - related to relief, tectonics, and hydromorphic influence (fig. 6, photo 3). Like in other parts of Thailand, alternating sedimentation and erosion processes and also 3 Figures 4 - 7 see annex 4 Harald Kirsch: Steps and Methods for the Identification of Potential Land-Use Units bioturbations - mainly by termites - seem to be a main cause for the development of multi-layered soil profiles (KIRSCH 1998). 4. Data interpretation To identify significant land use changes between 1992 and 1994, the results of both surveys were overlaid. Fallow land and mango orchards have been mainly unchanged in that period. Most of the land that was mapped as fallow plots in 1994 was normally used for annual crops two years before. Orchards were newly established on most formerly fallow land plots that came under cultivation in 1994 Photo 3: Lateritic gravel underlying a sandy cover layer (fig. 5). Land plots that have been allocated by the Land Reform Department (LRD) and were not used (fallow) during the 1994-95 cropping season were overlaid with the soil map to identify the respective soil types. To determine the reasons why the respective

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