A regional-scale analysis of vegetation types of the Northern Chihuahuan Desert in the context of the National Vegetation Classification
We conducted a regional-scale analysis of the vegetation communities of the Northern Chihuahuan Desert based on plot data compiled from 19 classifications and mapping projects in the region. These classifications span the arc of the northern Chihuahuan region and offered an opportunity to explore National Vegetation Classification (NVC) hierarchical relationships from the Macrogroup down through the Plant Association. Previously, some 3,000 Chihuahuan plots have been classified to the association level according to the latest NVC classification standard (FGDC 2008), but this had been done on a project-by-project basis, i.e., no regional analysis has been conducted to evaluate the efficacy of the plant associations and the alliances, groups, and macrogroups to which they belong. Yet, the need for a fully realized Chihuahuan Desert vegetation classification is in demand in the Southwest to support applied research activities that include modeling, mapping, climate change, and land use studies. We conducted multivariate floristic, environmental, and biogeographic analyses of plant associations and alliances, and revaluated them with respect to their regional consistency and placement in the current NVC hierarchy. We then evaluated the consistency of the middle levels of the hierarchy—divisions, macro-groups and groups—and made proposals for revisions to the NVC.
From the dataset, 319 plant associations were initially identified from among 25 alliances, eight groups and two macrogroups (Chihuahuan Desert Scrub and Chihuahuan Semi-Desert Grassland). This represented a highly refined classification of associations, of which only 60 were currently accepted in the NVC. Fuzzy cluster analysis and indirect ordinations of floristic data revealed that many of the remaining associations and some of the accepted ones could be lumped without loss of the underlying essential concepts in the original studies, while adding coherency to the concepts across the region. This was particularly the case with units represented by a limited sample pool. We recommended that 54 new associations be accepted into the NVC and an additional 45 be recognized as provisional pending additional data. With respect to the middle levels of the NVC hierarchy, we recommended that the broadly defined Chihuahuan Desert Foothill-Piedmont & Lower Montane Grassland Group be split into separate foothill versus piedmont groups based on species composition and physiognomy of the component associations. Results and revision recommendations will be submitted to the ESA Vegetation Classification Panel NVC Peer Review Board for consideration, and plot data will be entered into VegBank, the national vegetation plot database.