Ecological Site Descriptions
Montana’s Ecological Site Descriptions are in the process of being revised from the Rangeland Resource Unit (RRU) system to the Land Resource Unit (LRU) System.
Land Resource Unit System (LRU)
An Ecological Site is defined as a distinctive kind of land, with specific physical characteristics which differ from other kinds of land in its ability to produce a distinctive kind and amount of vegetation, and in its response to management. The Montana statewide ecological site key is linked below and should be used in identifying ecological sites in Montana.
Major Land Resource Areas (MLRAs) and the associated LRUs are the basic units for delineating statewide patterns of soils, climate, water resources, and land use. Elevation, topography, and rainfall (effective amount, timing, kind and distribution) have been the primary factors used to delineate these LRUs in Montana, because of their affect on potential native plant communities, land uses, and water resources.
It is important to note that LRU determinations cannot and should not be made by solely evaluating the plant community present on the site at the time of inventory. The LRU determination must be made only after evaluating the soil moisture and soil temperature regimes, the amount of effective precipitation the site receives on a climatological basis (not annual weather fluctuations), the timing of precipitation (ratio and distribution of spring, summer, fall and winter precipitation), the kind of precipitation (rainfall or snow), and the length of the active plant growing season. All of these factors are evaluated apart from the plant community on the site to determine the LRU that the ecological site is within. The plant community is an expression of these soil and climate influences (at the LRU level), in addition to other factors that are considered at either the MLRA level (e.g., geology) or at the site level (e.g., soil chemistry, depth, landscape position, etc). The ecological site development policy guide and MLRA map are linked below and provide more information
More information and definitions regarding Major Land Resource Areas and Ecological Site Descriptions are available from the NRCS soil survey and rangeland management programs.
If you encounter any problems with the files provided on this page, please contact Technical Resources at 406-587-6822.
The following documents are available in Adobe Reader format.
MLRA Rangeland Ecological Site Key (PDF; 24 KB) (Updated May 2013)
ESD-LRU Matrix by MLRA (PDF; 87 KB) (New July 2010)
Montana Ecological Site Development Policy (PDF; 778 KB)
Major Land Resource Areas (A printer-friendly version of the current MLRA LRU map.) (PDF; 1.4 MB)
Montana Rangeland Resource Unit System (RRU)
Note: The Montana RRU system is incrementally being replaced by the ESD-LRU system.
Montana ecological site description are currently organized into five large Rangeland Resource Units: West, North, Central, South, and East. Each of the five large units is divided into more basic Rangeland Resource Units along Major Land Resource Area (MLRA) boundaries. Divisions are determined on factors such as precipitation (kind, timing, and amount), temperatures, plant functional groups (cool season grasses versus warm season grasses), etc.
To access the ecological site descriptions for a basic Rangeland Resource Unit, select the appropriate spot on the map or skip to the text links below.
Montana Rangeland Resource Unit and MLRA Map
Montana Rangeland Resource Unit and MLRA List