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Managing Land Cover Map Units Among States, Regions, and the USNVC

SHANNON MENARD

Association for Biodiversity Information, Minneapolis, Minnesota

The U.S. National Vegetation Classification (USNVC) is the standard for mapping vegetation for
the Gap Analysis Program (GAP). The objective for mapping vegetation units is the alliance
level of the USNVC. The Association for Biodiversity Information (ABI) maintains the
classification system. Many state projects conducted their land cover mapping prior to
establishment of the NVC or complete identification of alliances for their region. Commonly,
states have not been able to map all individual alliances across the entire state and so have
created mosaics of alliances or mapped at the formation level (the physiognomic level above
alliance in the USNVC). Some states are able to map some units at the association (a finer
floristic unit than alliances in the USNVC).

The variation in map categories among states and regions has created a need to develop cross-
walks to the classification standard. In order to develop regionally consistent, ecologically
meaningful map units, ABI ecologists are working with individual projects to link different state
data through a common platform. To this end, ABI scientists are creating Access databases that
will contain map units from several states cross-walked to alliances, which will give GAP a
common unit to produce regional maps.

I created an Access database to manage state classification/map units in relation to USNVC
alliances in the Great Plains and Southeast. This database links directly to USNVC data and will
update each time USNVC is revised. I received alliance and map category information from
several Great Plains states (SD, ND, KS, NE, MO, and IA). Data from other states in the Great
Plains (and the Midwest) will be solicited and added to the database during the next year. Data
from some southeastern states have been incorporated (TN, NC), and Milo Pyne (Vegetation
Ecologist, Southeastern Region, ABI) is in the process of gathering data from the rest. This
database can be used to update the information provided by state GAP projects (some projects
had out-of-date USNVC information), locate map units not cross-walked to the USNVC, and
identify alliances defined by states that are not currently defined in the USNVC. Reports linking
data from several states can list state information/data in various formats. These reports can be
sent to state/regional projects once data have been finalized for those states. This database will
continue to efficiently track and manage the alliance data, compositional groups, and ecological
complex data needed to develop multiscale land cover mapping units across the regions and can
be used to develop regional map units. Using this database as a template, a similar database is
also under development in the West to manage information from the Southwest ReGAP project.
In the future, these databases can be combined to track the GAP map units and their relationships
to the USNVC nationwide and thereby help GAP define regions for remapping or regionalizing.