|The Improvement of Tropical and Subtropical Rangelands (BOSTID)|
|Regional resource assessment|
The objectives of the resource assessment, which are to provide information for general planning, are:
· To determine the general nature and condition of the
resource base in the project region;
· To identify the areas within the region that are of special concern;
· To establish the relative importance of each area according to the objectives of the project; and
· To develop a realistic plan of action based on the assessment.
Maps and supplementary reports are the products of the resource assessment. The maps show the location and extent of different types of land in relation to other lands. Because a general overview is required, map scales are commonly smaller than 1:100,000.
In the mapping phase of a resource assessment, the region is surveyed and divided into areas that are relatively homogeneous in some property such as vegetation, soil, or land use. At the scales considered here, however, only broad patterns can be mapped. Mapping units will be somewhat heterogeneous and will contain a number of different site types. An important purpose of the report is to relate this diversity by describing the nature and composition of the mapping units.
Mapping units are not necessarily predefined and may be designed to meet the needs of a project. These mapping units will become the physical units around which the study project is organized and probably will become the units used for many future land management decisions. Thus, criteria used to define basic mapping units must be carefully selected. In a resource assessment for range improvement, units should contain areas that (1) have about the same capacity to sustain one or a set of land uses, and (2) require similar kinds of management. This characteristic of land is generally called "land capability" and is determined by a number of factors, such as climate, vegetation, wildlife, and soil.
Climate is perhaps the most important factor in determining land capability because of its direct impact on the immediate resource, such as forage, and its role in determining the types of vegetation and soil found in a region.
The climatic data required for a resource assessment are those that influence the development of soil and the distribution of vegetation. Average annual temperature, seasonal extremes, frost-free period, evaporation, and precipitation amounts and their seasonal distribution are the most important considerations because they help determine soil type, water availability, vegetation type, and potential plant productivity.
Although climate is important in determining land capability, only broad generalizations are expected at the resource assessment level. The purpose is to identify relatively homogeneous climatic zones that could support one or a limited set of vegetation types.
Since climate cannot be observed directly, vegetation patterns often are mapped and interpreted as indicators of climate. Many assessments produce a composite map of climate and vegetation. Intended to serve as an indicator of climate, it is also an important management tool. An examination of the environmental history of the region and previous resource assessments, as well as an interpretation of the information generated during the mapping phases of the resource assessment, allows the development of a profile of the type of vegetation that might be found in different parts of the region under "natural" conditions. This model of potential or climax vegetation ultimately may serve as a guide for range improvement by suggesting what might be achieved.
It is also necessary to inventory actual vegetation patterns currently found within the region. A vegetation inventory includes maps and descriptions of associations, at a minimum, and could also include information on cover, production, and numbers of plants. Special attention should be given to determining the value of component species for forage, fuel, and other uses.
At this level of study, the goal is to provide information on the distribution of resources and, by comparing the results with the estimate of potential or climax vegetation, to identify areas where there are opportunities for range improvement, and to indicate areas where problems exist. Perhaps most important, the inventory of actual vegetation provides a picture of conditions at the beginning of the project that can serve as a benchmark for measuring general progress during the course of the project.
At the resource assessment level, geology is described in general terms. Primary consideration is given to identifying rock type and structure within the region. Geologic information provides a structural framework for the region and also is used to help form a general understanding of regional hydrology and the evolution of landforms and soils by providing clues to the origin, age, and mineralogical composition of surface materials.
Landform is the feature commonly used to unify or provide a framework for the mapping aspects of the resource assessment. In most cases, landform is the most readily mapped feature of the landscape, and it is frequently correlated with other, less easily observed features, such as hydrology or soil. Not surprisingly, some vegetation types within the region may be consistently associated with a particular soil. Thus, an understanding of regional landform-soil-vegetation relationships is a powerful and necessary tool in developing the physical base of a resource assessment. An analysis of information on landform provides a general framework for survey while indicating some of the areas that might be especially susceptible to erosion. These areas would warrant special attention in a range improvement project.
Along with climate, soil type ultimately determines land capability. At the resource assessment level, however, only general soil information is gathered. This includes soil texture, soil morphology (that is, depth and presence of limiting horizons), general soil chemistry, and susceptibility to flooding or erosion. Ideally, many soil properties can be inferred from climate, landform, slope, and existing land use.
Soil types are not mapped at the resource assessment level unless the environment of the region is very simple. More typically, natural groupings of soil types, such as soil associations, are mapped. Although soil types are not mapped, descriptions of them are acquired to portray the range of conditions that will be found within the broader mapping unit.
Delineation of watershed boundaries, major drainage lines, and other hydrologic features (for example, dry lakes) can help develop a general hydrologic framework of the region; it can also help facilitate the interpretation of landforms and soils, and can provide a general view of the likely distribution of water resources.
In most arid and semiarid regions, the distribution and quality of surface and near-surface water in an area will restrict the number of options for range improvement and subsequent management, and will have a major influence on the course of the project. Thus, a resource assessment must locate sources of surface water such as springs, streams, lakes, ponds, impoundments, and irrigation works, as well as average seasonal flows or volumes. Proven subsurface resources also must be reported by noting the location, depth, and yield of wells.
Current and Historical Land Use
Descriptions of land use are important for at least three reasons. First, one of the primary purposes of the resource assessment is to provide an overview of the mix of regional land uses. A comprehensive description of land uses will provide a general reference and may suggest functional economic linkages between land uses, such as irrigated agriculture and animal grazing systems. Any range improvement project must consider the relationships that exist between adjacent land uses.
Second, the land uses and management practices found within a region give some indication of variations in land capability. For example, pastures that are used only seasonally may be limited in their productivity because of cold winters or spring flooding. Such lands would require special consideration.
Third, some range improvement problems are associated with specific land uses, such as urban developments and woodcutting in many places, and should be identified for special treatment.
Like climate, some land uses are difficult to observe. Because of the ambiguous distinctions between some types of vegetation and land use (rangeland, for example), they are sometimes mapped together. A common compromise is to map "land cover," which includes all observable features that cover the land surface, such as vegetation, surface water, and various land uses (urban development or agriculture, for example).
Information on current land use should include maps and descriptions of all land uses, settlements, infrastructure (roads, canals, rail lines, fences, wells, and other watering points), and population estimates. Descriptions of regional land tenure practices may also be useful in explaining some land use patterns and management problems.
The patterns observed now may not be directly attributed to current land use practices. Historical events or land uses that are no longer observable may have left profound impacts on the land.
For example, highly saline rangelands may have been irrigated at one time and later abandoned because of salt accumulation. Thus, a general description of previous land uses, land use practices, and their locations may be useful in understanding current problems. Moreover, the successes and failures of the past may provide good evidence of what might be expected and how changes in management alternatives might be developed during the project.
Livestock and Wildlife
At the resource assessment level, it is necessary to produce a general census of animal herds within the region. Information gathered might include herd location, size, composition, general condition, and seasonal movement. In addition, the forage preferences and consumption patterns of the largest groups and their place in the local economy should be noted. With this information, range resources can be described in terms of forage demand, and the general economic and social impacts of alternative animal management plans can be projected.