Assigning Coefficients of Conservatism to the Flora of the Middle Rio Grande
Jessica Stern1*, Jeffrey Matthews 1, Brook Herman2
1 University of Illinois at Urbana-Champaign, Urbana, IL, USA; jlstern2@illinois.edu; jmatthew@illinois.edu
2 Engineer Research and Development Center, U.S. Army Corps of Engineers, Vicksburg, MS, USA; Brook.D.Herman@erdc.dren.mil
Floristic Quality Assessment (FQA), a method for surveying the quality and integrity of natural areas, is a useful tool for land managers for guiding the management of different habitat types. FQA uses plant Coefficients of Conservatism (C-values) to assess the level of anthropogenic disturbance of a given natural area, as well as to assess that area’s quality and desirability for management or conservation. C-values are assigned a priori to all plant species in a region, usually a state or an ecoregion, by expert regional botanists. These C-values express a species’ degree of tolerance to anthropogenic disturbance. C-values currently have been created for much of the United States east of the Rocky Mountains, as well as in Colorado and in parts of Montana, however, there is currently a gap in the Southwest. Our aim was to help close this gap by establishing C-values for the flora of the Middle Rio Grande floodplain in New Mexico, from south of the Cochiti Dam to the Elephant Butte Dam.
In 2018 we compiled a list of species found in the Middle Rio Grande floodplain. Four regional botanists were sent this comprehensive list to review, and the finalized list (n=624) was sent to two regional botanists for C-value assignment. Botanists were asked to assign C-values on a scale from 0-10 (0 reserved for non-native taxa and/or the least conservative native taxa, and 10 being the most conservative). After two rounds of C-value assignment, C-values were averaged between the two assigners. Descriptive statistics were calculated, and correlation analysis was used to examine the relationship of C-values assigned between the two rounds, as well as shared species between Colorado (CO) and New Mexico (NM).
A total of 486 native species were assigned values, and 138 non-native taxa were assigned a value of zero. Our findings are consistent with the disturbance history of the region, with the most frequently assigned C-value of 4 (145 species) and the majority of native species placed within the 4-6 range of moderate tolerance of anthropogenic disturbance. Results from the correlation analysis between NM and CO show a significant, but weak, positive relationship between the values for the two states, highlighting some ecoregional similarities between the two states and providing a basis of comparison for the C-values we created. Overall, we created C-values that are another tool in the land manager’s belt for managing and evaluating riparian restorations along the Middle Rio Grande.