3.4 Defining Revegetation Units

Revegetation units are areas with similar revegetation treatments and environment (e.g., soils, climate, and vegetation potential). In mountainous terrain, there may be several revegetation areas in a mile of roadside due to changes in aspect, soil type, and road drainage. Roads in mid-western states, however, often have only one revegetation unit that may encompass much of a project area because of the uniformity of the landscape. The first step in developing a revegetation unit is grouping major soil types together with similar characteristics important for reestablishing native plant communities. For example, a project site with a group of soils that are less than a foot deep would have a different set of revegetation treatments than deeper soils and for that reason would be identified as a revegetation unit based on soil depth. Grouping soils into revegetation units can also be done through the Ecological Sites section of the Web Soil Survey. As described in Figure 3-5, a soils map and report are created on the Web Soil Survey by delineating the project area on the interactive map of the U.S. At the same time, a map can also be produced that groups soils by similar capabilities to create distinct plant communities called "ecological sites". The ecological sites section of the Web Soil Survey also lists the major native species for each ecological site for many parts of the U.S.

Revegetation units also designate areas that have the same revegetation objective. For example, a road project may include a constructed wetland for maintaining or improving water quality. In another area, the objective may be to enhance pollinator habitat. These areas would be designated as separate revegetation units because they would have different revegetation treatments and species, which might include a pollinator species mix for the pollinator habitat unit and an erosion species mix for the wetland unit. In addition, soil improvement treatments for the wetland would be developed to enhance wetland species and maintain the proper functioning of a constructed wetland. This may include creating manufactured soil that is specific to wetland species and water filtration.

Road components also play a large role in delineating revegetation units. In mountainous terrain, cut slopes and fill slopes are often designated as separate revegetation units because of the differences in soil depth, slope gradient, and road drainage between the two slopes. Table 3-5 shows revegetation units commonly associated with the components of a road.

The revegetation plan includes a revegetation unit map that locates revegetation units on the road project map (Figure 3-8). The revegetation plan further describes the soils, climate, and vegetation of each revegetation unit and how the revegetation objectives will be met.