MSL-USDA NRCS Natural Resource Data Partnership Natural Resource Inventory

Landscape Level Ecological Units

Ecological Unit mapping is a classification system for stratifying the Earth into progressively smaller areas of increasingly uniform ecological site potentials. Ecological unit categories are delineated based on associations of biotic and environmental factors that directly affect or indirectly express energy, moisture, and nutrient gradients which regulate the structure and function of ecosystems. These factors include climate, physiography, water, soils, air, hydrology, and potential natural vegetation communities. Over the past three decades environmental scientists have developed several versions of ecological unit mapping at differing scales for the United States. The most commonly used ecological unit mapping products for Montana are provided here.

USFS Ecological Unit Hierarchy

This Ecological Unit Hierarchy mapping is based on the USFS National Hierarchical Framework and uses the Domain, Division, Province, Section and Subsection levels of increasing refined ecological map units.

EPA Ecoregions

The ecoregions mapped by the DOI EPA are areas where ecosystems are generally similar and were designed as a spatial framework for the research, assessment, and monitoring of ecosystems and ecosystem components. These ecoregions denote areas of similarity in the mosaic of biotic, abiotic, terrestrial, and aquatic ecosystem components with humans considered as part of the biota. These regions were designed for structuring and implementing ecosystem management strategies.

USDA Major Land Resource Areas (MLRA)

The USDA MLRA’s represent landscape level geographic areas with distinct physiography, geology, climate, water, soils, biological resources and land use. These delineations are incorporated into the distinctions between soil map unit level ecological sites.

The latest version (5.2) of the MLRAs was published in 2022.  Previous versions were published in 2006 (4.2), 1981, and 1965. 

Montana Ecological Groups

The Montana Ecological Group mapping is based on key attributes of the MLRAS, Ecological Units and Ecoregions with refinements made in mapping and attribution to further define ecological units with Montana specific information and accommodate key biophysical distinctions useful for Statewide ecological characterization and analysis.


SSURGO data depicts information about the kinds and distribution of soils on the landscape. These data sets are digital soil surveys and are the most detailed level of soil geographic data developed by the National Cooperative Soil Survey. The map data include a detailed, field verified inventory of soils and miscellaneous areas that normally occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped.

Interpretive Soils Maps

  • The statewide Drainage Class map represents the drainage class for soil map units
  • The statewide Farmland Class map represents the farmland class for soil map units
  • The statewide Relative Slope map represents average slopes for soil map units
  • The statewide Hydric Class map displays the percentages of hydric components for soil map units