PS 55-94
Vegetative classification of the Pawnee National Grassland, USA
Species respond individualistically to environmental and geographic gradients, biotic interactions, and disturbances. However, plant species are often located in assemblages along environmental gradients based on their life history characteristics. Based on these assemblages, vegetation communities may be classified and such classification allows managers to parameterize community characteristics to document their locations and monitor changes. To date, no plot-based classification has been attempted for the Pawnee National Grasslands in northeastern Colorado, so this base-line knowledge is lacking. Gaining an understanding of the complex nature of Colorado’s shortgrass steppe will enable land stewards to accurately assess impacts from disturbances. We sampled 128 plots throughout the Pawnee National Grasslands, including 26 plots from prairie dog colonies, and subsequently developed a classification of plant community types. Data collection followed the Carolina Vegetation Survey procedure and data were analyzed using clustering and NMS ordination (using Bray-Curtis similarity) as well as species indicator analyses to develop community types. We attempted to examine effects of environmental factors, including grazing, prairie dog colonies, and old buffalo wallows on the classification. Our local classification was compared to the USNVC to imbed our results into the national system.
Results/Conclusions
Richness for all plots was 299 species out of a known 430 that are found on the Pawnee. A moisture gradient was found that ranged from more mesic sedge and Pascopyrum smithii-dominated types (with similarities to the mixed grass communities) to sparse, dry rock outcrops with high species diversity. As expected, the dominant species found consistently along the gradient were Bouteloua gracilis and Bouteloua dactyloides. A total of nine community types were identified and related to environmental factors, and seven of these types matched well with the US National Vegetation Classification associations. Buffalo wallows, prairie dog colonies and general ungulate herbivory led to variation within classified types, but did not render new types, probably due to the long evolutionary history between plants and animals on the shortgrass steppe. Based on significant relationships with longitude and topographic factors, a prediction of community types was modeled [mapped] onto a GIS landscape. While exotics were found, they were mainly restricted to the most mesic areas of the landscape, suggesting the intact xeric shortgrass steppe is not easily invaded.