The FGDC Vegetation Classification Standard requires federal agencies to crosswalk vegetation plot data, existing vegetation types, and map units to the lowest possible level of the U.S. National Vegetation Classification (NVC). The Chief of the U.S. Forest Service has ordered regional ecologists to crosswalk to the Macrogroup level by September 30, 2017. In the Intermountain Region of the Forest Service, existing vegetation is classified to dominance types based on the species with the plurality in the uppermost layer. Individual National Forests may subdivide regional forest dominance types into phases based on a second tree species. These types are similar in detail to NVC Alliances, but based on different criteria. The Region’s vegetation plot database currently contains 18,300 characterization plots with complete species list, and 39,283 observations with partial species lists. This project was undertaken to develop methods for assigning vegetation plots to US NVC Macrogroup, Group, and Alliance using database queries. A list of all NVC types occurring in the Intermountain Region was compiled using a spreadsheet with the entire US NCV and deleting types not occurring in the region by reading descriptions at http://usnvc.org. NVC type descriptions were then used to develop database queries to assign plots to Macrogroups.
NVC type descriptions are generally qualitative in nature but database queries require qualitative values for terms such as dominant and codominant. The lack of quantitative descriptions required an alternate approach comparing the NVC associations belonging to each alliance to our plots’ assignment to Forest Service community types and associations based on potential natural vegetation (PNV). Entering the NVC at the Alliance and Association levels was much easier that starting at the Class level and working down the hierarchy. Relationships between Forest Service dominance types and phases are generally many to many due to the differing criteria used by each system. For example, the Aspen regional dominance type cross-walks to 3 Macrogroups, 9 Groups, and 12 Alliances. Across 12 national forests, there are 23 dominance type phases for aspen or aspen-conifer forests. These cross-walk to 16 NVC Alliances. Individual dominance type phases crosswalk to 1 to 10 Alliances. Individual Alliances crosswalk to 1 to 13 dominance type phases.
Forest Service dominance types are designed to existing vegetation for land managers at a forest wide or planning scale. Cross-walking our dominance types to the NVC is informative. Assigning plots to the NVC can inform the refinement of Alliances and Groups.