02 Contents Frame
v-vi. Description of land mapping units and land qualities
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40 2019 ND-CP 413905
| v-vi. Description of land mapping units and land qualities
These stages correspond to the land resource survey. The objectives of such surveys are to define and delineate boundaries of land mapping units and to determine their land qualities. Most land evaluation studies require physical resource surveys; in some cases sufficient information may be already available. The surveys will generally include a soil or soil-landform survey, and sometimes pasture resource or other ecological surveys, forest inventory, surveys of surface-water or groundwater resources, or road engineering studies. Participatory approaches, in which the insights and information of land users and surveyors are integrated, will provide the most directly relevant results. The success of the integration depends very much on the quality of the base maps. It is necessary to start from accurately identified reference locations, by preference on detailed topographic maps, rectified aerial photos or detailed satellite images. The delineation of land mapping units will be based in part on land characteristics most readily identified –frequently landforms, soils and vegetation. However, at the stage of resource survey, the land qualities believed to have significant effects on the types of land use under consideration have already been provisionally identified; consequently, special attention should be given to those qualities during field survey. For example, in surveys for irrigation projects, particular attention is given to the physical properties of the soil, to the quality and amount of available water and to the terrain conditions in relation to methods of irrigation considered. Suitability classes may be defined in terms of land qualities or land characteristics, as defined and illustrated in the original Framework (pp.12–13). From a systems point of view, land qualities are to be preferred, but some studies have found land characteristics simpler for the evaluator and more easily understood by users of the evaluation. Thus, plants respond to the land quality of moisture availability; mean annual rainfall is an important land characteristic affecting this, although by no means the only one. In some cases land qualities and characteristics are closely similar, as where the quality soil salinity is assessed by the characteristic topsoil salt content. Some studies have shown that evaluation for the same land uses carried out using qualities and using characteristics produces very similar results (Sys 1978; Sys et al 1991a, b, 1993). Land evaluation – towards a revised framework 36 It is preferable to use land qualities wherever possible, since the use of land characteristics often involves hidden assumptions (e.g. if rainfall alone is used to assess moisture availability, an assumption that soils are of similar texture, depth, slope, infiltration rate, etc). However, land characteristics, or a mixture of qualities and characteristics, may be found appropriate in some instances. The concept of land qualities –assessed by means of land characteristics, as commonly applied to crop and forest production– can be employed equally when assessing environmental services. For example the land quality ‘remoteness’ or ‘isolation’, relevant to assessing suitability for a nature reserve, could be assessed by the land characteristic distance from the nearest road; the land quality ‘Potential water yield’, relevant to assessing suitability for preserving land for rainwater harvesting, could be assessed either directly, by gauged river flow, or where there are no such measurements, by some combination of available data including rainfall, vegetation and soil characteristics. tải về 0.57 Mb. Chia sẻ với bạn bè của bạn:
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