There is a growing interest in exploring inter-relationships and mutual applications between US National Vegetation Classification (USNVC) hierarchy and Ecological Sites Descriptions (ESDs) and associated State Transition Models (STMs). This is driven, in part, by maturation of both efforts into operational frameworks that offer opportunities for meaningful engagement that may benefit of both systems. With respect to the USNVC, following FGDC National Vegetation Classification Standard, Version 2, the ESA Vegetation Classification Panel rolled out the classification on the web for use by federal agencies, state partners, and the public (http://usnvc.org/), and they are developing mechanisms for on-going updates and additions to the content. Similarly, Ecological Site Descriptions and associated state transition models have been developed over the past several decades as part of the US land-type classification system that describes ecological potential and ecosystem dynamics of land areas and are now being adopted widely across agencies. To explore potential linkages between the USNVC and Ecological Site hierarchies, I present a case study from the Chihuahuan Desert region based on 1,120 vegetation plots in combination with ecological site information.
Focusing on the Chihuanhuan Semi-desert Grasslands Macrogroup (M087) from the fifth level of the USNVC hierarchy, I conducted a meta-analysis of 90 plant associations belonging to four lower-tier USNVC Groups (G490 Chihuahuan Desert Foothill-Piedmont & Lower Montane Grassland; G492 Chihuahuan Gypsophilous Grassland; G491 Chihuahuan Sandy Plains Semi-Desert Grassland, and G489 Chihuahuan Semi-Desert Lowland Grassland) and four corresponding Ecological Site Groups (ESGS)—Gravelly, Gyspic, Sandy, and Loamy-Clayey, respectively. A DCA ordination and cross- tabulation analysis of landform, soils, and other site characteristics revealed that with the exception of G490, the USNVC groups were well characterized floristically and compared well to corresponding ESGs. I further decomposed G490 by plant association and identified a subset that are limited to foothills that correspond well to the Bedrock-Colluvial ESG with the remainder corresponding to the Gravelly ESG. These preliminary results suggest that there are potentially mutually beneficial linkages between the USNVC and the ESG hierarchies. The results will also help inform a set of planned pilot studies across the continental United States that will compare and further test linkages between the two systems.