Land Suitability Identification for a Production Forest through GIS Techniques  N D K Dayawansa Department of Agricultural Engineering, Faculty of Agriculture, University of Peradeniya Peradeniya, Sri Lanka Tel: +94-777801712, Fax: +94-8-387216 Email: dammid@pdn.ac.lk G K Ekanayake Introduction Uses of the land to humankind are multi-facet. As a source for primary production system, it serves as a store of water and nutrients required for plants and other living organisms. Proper use of land is essential to obtain the maximum benefit out of it. The proper use includes growing of suitable crops and plants, efficient soil & water conservation measures etc. Land as a resource cannot be measured by the surface area alone, hence the types of soil which is critical for productivity, underlying geology, topography, hydrology and plants and animal population also have to be considered. These attributes limit the extents of land available for various purposes. The growing population, industrialisation and misuse & overexploitation of land resources have in effect increased the demand for land. The total land area in Sri Lanka is 6.56 million hectares. In Sri Lanka, population increase has significantly changed the use of land since independence. The per capita land availability in the country in year 1871, when the population was 2.4 million was 2.7ha. It has reduced to 0.38ha in year 1991 when the population was 17 million. This value is expected to be going down further with the forecasted growth of population (Natural Resources, Energy & Science Authority of Sri Lanka, 1991). The degradation of land resource due to overexploitation & misuse and consequent economic, social and environmental impacts have intensified the pressure on the land resources in the country. Cultivation and settlements in unsuitable land is a grave problem in major upper watershed areas. This has been identified as a significant threat to the productivity of land and also to the downstream reservoirs constructed for hydropower generation and irrigation purposes. The lifespan of the reservoirs can be reduced considerably due to siltation as a result of high soil erosion in the headwater areas. Water quality problems have also been encountered in major agricultural areas as a result of over-fertilisation (Department of Census & Statistics, 1998). It has been observed in Sri Lanka that the extents under agriculture and human settlement and other uses have gone up and the extents under forests and wildlife conservation have gone down rapidly. This clearly illustrates the fact that the growth of agriculture and other human activities have exerted pressure on the extents under forests and wildlife conservation. Therefore, it is of paramount importance to identify suitable land for various uses in optimum utilisation while causing minimum impact to the environment. Land Suitability Evaluation The first stage in evaluating land and preparing a land-use plan to gather data to classify the land according to their use is called land suitability. Land capability, which is also considered as land suitability (FAO, 1978) is primarily the potential biological productivity of land. Productivity of land can be determined by four main components of the environment namely climate, local topography (ruggedness, steepness, exposure-which cause local variation in climate and disposition of soil type), soil and existing vegetation. Land suitability evaluation involves identifying land use patterns and the economic & environmental feasibility of its current use. Land Suitability Mapping with GIS Traditionally, spatial data has been acquired and rendered into pictorial form to accomplish variety of activities related to land resource management. With the introduction and dissemination of high speed computers and of data capture and display devices, the importance of developing a computer based system of efficient and cost effective land resource data management was emphasized. As a result, database systems for spatial data, commonly named as Geographical Information system (GIS) were designed and developed enabling the acquisition, compilations analysing and displaying topological interrelations. Therefore, it is apparent that the accomplishment of almost any project aimed at land resources planning may be greatly facilitated by the use of and efficient GIS. Useful land suitability assessments cannot solely be based upon biophysical resource information. Transportation networks, scale dependent localised economies, and social factors such as education and demographics dealing with large number of spatially related information have also to be considered in this process (ESRI, 2002). The surface and overlay analysis capabilities in GIS can effectively facilitate in handling this vast amount of spatial information. Today, remote sensing and are playing a very significant role in land evaluation systems such as production of land suitability maps (Perera & Tateishi, 1994).
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