Ecological sections are a mid-scale ecological classification and mapping unit of the National Hierarchical Framework of Ecological Units (ECOMAP 1993). This framework consists of progressively smaller mapped units nested within a hierarchy. The eight possible levels within the hierarchy each have a distinct scale; unit delineations within the levels are based on the most important ecological factors operating at that scale.

An essential concept of the hierarchical approach is that the ecological factors defining a larger scale unit (like climate) also control the ecological potential of units nested below. At the largest ecoregional scale (Bailey 1995), units have a size of thousands or millions of square miles and are dominated by broad patterns in climate and landform. Subregional scale ecological sections (McNab and Avers 1994) and subsections (Nesser et al. 1997) are based on mid-scale patterns of climate, geology, and landform. The ecological sections displayed here for Montana form units of tens of thousands of acres in size each with a repeating matrix of typical vegetation communities. The smallest landscape scale units like landtype associations are only measured in 10’s to a few thousands of acres and have quite uniform patterns of soils and vegetation. These have only been described in Montana for Forest Service land.