Land Resource Regions and Major Land Resource Areas
Land resource regions and major land resource areas are separated on the basis of significant differences in use and management of the soils as reflected in land use patterns. These regions and areas represent nearly homogeneous areas of soil, climate, land use, water resources, elevation, topography, and potential natural vegetation.
Land Resource Regions
Land resource regions (LRRs) are geographically associated groups of major land resource areas and consist mainly of areas that have very broadly related patterns of soil, climate, water resources, and land use. LRRs are delineated only on small scale national maps (1:7,500,000; 1:10,000,000; or smaller) and are most useful for national and regional program planning. LRRs are unique, continuous delineations, which approximate physiographic regions on small scale national maps.
Major Land Resource Areas
Major land resource areas (MLRAs) are based upon aggregations of geographically associated land resource units and identify nearly homogeneous areas of land use, elevation, topography, climate, water resources, potential natural vegetation, and soils. MLRA boundaries reflect an appropriate generalization of land resource unit boundaries (as derived from state soil geographic database map unit boundaries). The approximate minimum size of a MLRA that may be delineated is 580,644 hectares, or 1,434,803 acres. This minimum delineation is represented at the official MLRA map scale of 1:7,500,000 by an area approximately 1 cm by 1 cm (0.4 inch by 0.4 inch). Minimum linear delineations are at least 0.3 cm (0.1 inch) in width and 2.5 cm (1 inch) in length. The Pacific and Caribbean Islands, which have land areas less than 580,644 hectares (1,434,803 acres) in size are excluded from the minimum delineation rule. Large existing MLRAs may be subdivided to create more homogeneous areas as needed, provided that cartographic criteria regarding minimum delineations are met. The descriptions of the map units on MLRA maps emphasize land use and water resource management. Generally, an MLRA occupies one continuous delineation; but it may occupy several separate ones. MLRAs are most useful for statewide planning and have value for interstate, regional, and national planning.
Land Resource Units
Land resource units (LRUs) are derived from the aggregation of map units of the state soil geographic (STATSGO) database. This is possible because each STATSGO map unit has an MLRA designation in the STATSGO attribute file. The STATSGO-ARCMAP or ARCGIS Interface software is a useful geographic information system tool for generating the first draft of the LRU map from the STATSGO database. Based on a shared 1:250,000 scale, map unit boundaries on LRR maps mostly coincide with those in the STATSGO database. Land use exceptions are described in Section 649.02. Cartographic standards regarding the minimum size of delineations for LRU maps are equivalent to those for STATSGO. LRUs may occur as single delineations, but commonly occur as several separate delineations. LRU maps often depict areas that are cartographically too small to be delineated on the official MLRA map scale (i.e., 1:7,500,000). Therefore, LRUs are not shown on the national MLRA map. LRUs are shown only on State or soil survey regional office (SSRO) maps.
USDA Agriculture Handbook No. 296
USDA Agriculture Handbook No. 296, Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean and the Pacific Basin (see United States Department of Agriculture, 2006 in Exhibit 649-2), represents an assemblage of information currently available about the land for farming, ranching, forestry, engineering, recreational development, and other uses. This assemblage consists of the LRR and MLRA map and the supporting map unit descriptions. Such land resource information (both analog and digital) is used at national, regional, and State levels:
As a basis for making decisions about agricultural issues;
As a framework for organizing and operating resource conservation programs;
For the geographic organization of research and conservation needs and the data derived from these activities;
For coordinating technical guides within and between States;
For organizing, displaying, and using data in physical resource inventories; and
For aggregating natural resource data.
649.01 Policy and Responsibilities
Roles and responsibilities of offices within NRCS include the following:
The State Office, which—
Suggests changes in LRRs and MLRAs to the soil survey regional office; and
Assigns soil survey map units to the appropriate MLRA in the National Soil Information System.
The Soil Survey Regional Office (SSRO), which—
Submits suggested changes in LRRs and MLRAs to the National Soil Survey Center;
Obtains concurrence in suggested changes from other disciplines and States that share the LRR or MLRA;
Maintains the boundary, description, and documentation for each MLRA that is assigned to the MLRA soil survey regional office (as given in Exhibit 649-1); and
Provides the National Soil Survey Center with a small scale copy of the MLRA map for the responsible area.
The National Soil Survey Center, which—
Approves proposed changes;
Keeps current the LRR and MLRA maps and descriptions;
Maintains the area symbol, area name, and area acres for MLRAs in the National Soil Information System;
Periodically issues revised editions of Agricultural Handbook 296, which provides supporting attributes to these map products;
Provides the NRCS Resources Inventory Division an official copy of the LRR/MLRA data layers;
Keeps current the LRR and MLRA digital boundary maps; and
Provides assistance in maintaining the LRR and MLRA spatial maps.
The National Water and Climate Center, which—
Provides Parameter-elevation Regression on Independent Slopes Model (PRISM) data for new and/or subdivided LRRs and MLRAs to the National Soil Survey Center in a timely manner to facilitate revision of Agriculture Handbook 296 on the defined schedule.
The NRCS Resources Inventory Division, which—
Provides updated land use data on new and/or subdivided LRRs and MLRAs to the National Soil Survey Center in a timely manner to facilitate revision of Agriculture Handbook 296 on the defined schedule.
The National Technology Support Centers, which—
Provide a review of the updated sections of the LRR and MLRA descriptions prior to publication.
649.02 Land Resource Region and Major Land Resource Area Map Unit Descriptions
The LRR descriptions are summaries of the important characteristics of the MLRAs. They are maintained by the National Soil Survey Center.
The dominant physical characteristics of MLRAs are described under specified headings. Significant exceptions to these characteristics are described separately.
The extent of the land used for cropland, pasture, range, forests, industrial and urban developments, and other special purposes is indicated based on information provided from the most recent National Resource Inventory (NRI) and developed by the Resources Inventory Division of NRCS. The figures given are for the entire resource area unless stated otherwise. Also included is a list of the principal crops grown and the type of farming practiced. If significant, the relative extent of the federally owned land is indicated also based on NRI data.
The topography and natural features of each area are described. A range in height above sea level and relief, including significant exceptions, if applicable, are provided for the area as a whole. The extent of the four-digit hydrologic unit areas (see Seaber and others, 1987 in Exhibit 649-2) within each MLRA is given in percent. The major rivers and/or streams draining each MLRA and any National Scenic or National Wild and Scenic River reaches are also listed.
The bedrock geology and surficial geology of each MLRA is described. This information is derived from a wide variety of State and Federal maps and reports that are not included in the list of references.
A range of mean annual precipitation for the driest and the wettest parts of the MLRA and a range of the seasonal distribution of precipitation are given. Also given are a range of the mean annual air temperature and the average freeze-free period characteristic of different parts of the MLRA. The mean annual precipitation, the mean annual air temperature, and the average freeze-free period should be referenced according to weather station and to a specific collection of 30-year normals (such as from 1961 to 1990), as summarized by the National Water and Climate Center staff. These data are derived from Parameter-elevation Regression on Independent Slopes Model (PRISM) data and supplied to the National Soil Survey Center by the National Water and Climate Center staff located in Portland, Oregon.
Information is given concerning surface stream flow, ground water, and the source of water for municipal use and irrigation. Also, dependency upon neighboring MLRAs for water supply or ability to provide water to neighboring MLRAs is described. The extent and number of irrigation districts in the MLRA are given where pertinent. Also, the eight-digit U.S. Geological Survey Hydrologic Units are listed by relative extent.
Soils are identified according to the principal taxonomic great groups as referenced in the state soil geographic database. Soil series that are representative of each great group are listed, and the relationship of soils to landscape position is described.
Major plant communities within the MLRAs are described by dominant species utilizing common plant names (see Kuchler, 1985 in Exhibit 649-2). Common fish and wildlife species occurring within the MLRAs are also listed.
649.03 Land Resource Region and Major Land Resource Area Map Unit Names and Symbols
Traditionally, the names of LRRs and MLRAs reflect certain unique relationships to agriculture or forestry, but there is no set standard for names or terms.
Names of Land Resource Regions
The names of LRRs are combinations of names of broad physiographic provinces and predominant land use; for example, Northwestern Forest, Forage, and Specialty Crop Region.
Names of Major Land Resource Areas
The names of MLRAs commonly use the names of associated physiographic areas, landforms, and “natural geographic” areas; for example, Olympic and Cascade Mountains.
Symbols for Land Resource Regions
The symbols for LRRs are designated by capital letters; for example, A – Northwestern Forest, Forage, and Specialty Crop Region.
Symbols for Major Land Resource Areas
The symbols for MLRAs are designated by an Arabic numeral or by an Arabic numeral and a capital letter if previously established areas have been subdivided to provide for more homogeneous areas; for example, 9 – Palouse and Nez Perce Prairies or 63A – Northern Rolling Pierre Shale Plains.
649.04 Procedures for Establishing and Revising Land Resource Regions and Major Land Resource Areas
Proposals to change the existing LRR or MLRA map are submitted to the MLRA soil survey regional office responsible for the LRR or MLRA. Proposals for change can be requested by States or cooperators.
The responsibility for maintaining individual MLRAs is assigned to each SSRO, as listed in Exhibit 649-1. The SSROs that share the MLRA or LRR ensure that the maps displaying these areas are joined and coordinated across boundaries. The responsible SSRO coordinates suggested changes with appropriate staff of the National Soil Survey Center and regional members of the National Cooperative Soil Survey (NCSS).
The SSRO submits the following complete information to the National Soil Survey Center:
Documentation and justification for the requested change(s).
State LRU map that supports the suggested changes to the MLRA.—This is a computer generated film proof plot that shows LRU boundaries and symbols in black with an overlay showing the proposed MLRA boundaries and symbols in red. For the purpose of hard copy presentation, this map is made at a scale of 1:500,000.
Draft MLRA map with suggested change(s).—This is a 1:7,500,000 scale map generated from the most current approved digital version of the MLRA map. This map consists of a computer generated film proof plot showing proposed MLRA boundaries and symbols in red and the existing MLRA boundaries and symbols in black.
Complete draft of MLRA descriptions, including needed revisions to previously existing descriptions that are impacted by the proposal.
Letters from the SSROs of areas that share the MLRA.—These letters show concurrence on the change(s) and document a correct join if the change(s) affect the areas that share the MLRA.
Descriptions of changes that impact boundaries between SSROs or soil survey offices (SSOs).
Descriptions of changes that impact Common Resource Area (CRA) and LRU boundaries.
National Soil Survey Center Responsibilities
Justification and complete documentation must be received and reviewed at the National Soil Survey Center prior to approval by the Director of the National Soil Survey Center.
Approved changes are digitally incorporated into the existing MLRA and LRR maps on a 5-year cycle (e.g., 2010, 2015, 2020) and new map products are produced and released for official use.
A 1:7,500,000 scale proof plot and MLRA map unit descriptions that reflect the new revision are sent to the originating MLRA soil survey regional office for review.
When the products are returned to the National Soil Survey Center, the documented changes are made at the national level.
The center provides copies of the updated maps and documentation to appropriate NRCS users, NCSS cooperators, and others as requested.
All documentation supporting approved changes is archived by the National Soil Survey Center.
National Water and Climate Center Responsibilities
The National Water and Climate Center provides revised climate data from the Parameter-elevation Regression on Independent Slopes Model (PRISM) for mean annual precipitation, mean annual air temperature, and average freeze-free period for LRRs and MLRAs to the National Soil Survey Center as requested.
Resources Inventory Division
The Resources Inventory Division provides revised land use data for the modified LRRs and MLRAs to the National Soil Survey Center as requested.
649.05 Land Resource Unit Maps of States
Land resource units (LRUs) are the basic units from which MLRAs are determined (see United States Department of Agriculture, 2006 in Exhibit 649-2). They are based on significant statewide differences in climate, water resources, land use, potential natural vegetation, or other natural resource conditions. These factors contribute to significant differences in use and management of the units.
Major land resource area boundaries on State maps are identical and coincide with the boundaries on the national map. Because of the State’s needs to express the MLRA concept at a larger scale, the MLRA map units are disaggregated or broken down into LRUs. Land resource unit boundaries generally coincide with STATSGO database map unit boundaries with the following exception. STATSGO database map units may be subdivided into LRUs if there are significant and mappable differences in water resources, land use, or type of farming. Due to differences in scale, most MLRA and LRU boundaries are not exactly the same. However, MLRA boundaries should reflect an appropriate generalization of LRU boundaries, just as LRR boundaries should reflect MLRA boundaries.
Prescribed Scale of State Land Resource Unit Maps
The prescribed scale for state land resource unit map management generally is 1:250,000. In Alaska, LRUs are managed at a scale of 1:1,000,000. Land resource unit maps are derived from the STATSGO database and serve as a companion geographic information system (GIS) data set. LRU maps provide sufficient detail to permit their use for general planning of land resources at the State level. For the purpose of hard copy presentation, State LRU maps are made at a scale of 1:500,000.
Land Resource Unit Map Unit Names and Symbols
The conventions used in giving names and symbols to LRUs are based on the MLRA name and symbol. The LRU symbol uses the MLRA symbol followed by a hyphen, an Arabic number, and the State alpha FIPS code. For example, 144A-1NY would represent the first land resource unit in major land resource area 144A in New York. This LRU map unit name would be New England and Eastern New York Upland, Southern Part, LRU-1NY. Land resource unit map unit names and symbols are specific to each State. Therefore, LRUs may not be presently referenced in place of MLRAs on national data sets, such as the National Resource Inventory or the range site data set, which require correlation across State boundaries. Because of the need to coordinate field office technical guides across State boundaries, LRUs, unless they are coordinated with adjoining States, have limited application for this purpose.
Procedure for Establishing Land Resource Units
The state conservationist establishes the procedures for developing and maintaining LRU boundaries and descriptions. Procedures and criteria are similar to those used for establishing MLRAs at the national level but are at a larger scale.
Exhibit 649-1—A List of Major Land Resource Areas Assigned to Each Soil Survey Regional Office (SSRO)
All existing official MLRAs (circa 2006) and their descriptions will be regionalized in STATSGO and reviewed in a statewide forum of participants within the context of Interagency Ecological Mapping.
Exhibit 649-2—References (available from the National Soil Survey Center)
Jensen, S. 1992. One-Half Kilometer DEM Coverage for the U.S. USGS. EROS Data Center, Sioux Falls, SD.
Kuchler, A.W. 1985 (revised). Potential Natural Vegetation. In National Atlas of the United States of America. Dep. of the Int., U.S. Geol. Survey.
NOAA Staff. 1962. Monthly Normals of Temperature, Precipitation, and Heating and Cooling Degree Days, 1931-60. In Climatography of the United States No. 81. U.S. Dep. of Com., Nat. Oceanic and Atmos. Admin., Nat. Climate Data Center, Asheville, NC.
NOAA Staff. 1972. Monthly Normals of Temperature, Precipitation, and Heating and Cooling Degree Days, 1941-70. In Climatography of the United States No. 81. U.S. Dep. of Com., Nat. Oceanic and Atmos. Admin., Nat. Climate Data Center, Asheville, NC.
NOAA Staff. 1982. Monthly Normals of Temperature, Precipitation, and Heating and Cooling Degree Days, 1951-80. In Climatography of the United States No. 81. U.S. Dep. of Com., Nat. Oceanic and Atmos. Admin., Nat. Climate Data Center, Asheville, NC.
NOAA Staff. 1992. Monthly Normals of Temperatures, Precipitation, and Heating and Cooling Degree Days, 1961-1990. In Climatography of the United States No. 81. U.S. Dep. of Com., Nat. Oceanic and Atmos. Admin., Nat. Climate Data Center, Asheville, NC.
Seaber, P.R., F.P. Kapinos, and G.L. Knapp. 1987. Hydrologic Unit Maps. Dep. of the Interior, U.S. Geol. Survey.
United States Department of Agriculture, Natural Resources Conservation Service. 2006. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.