Floristic Variation Among Gravel Bars in a Subalpine River, Montana, USA

The presence and abundance of plant species on active geomorphological surfaces, such as fluvial gravel bars in subalpine rivers, may reveal different effects of the environment, location, and chance on the assemblage of species during succession. Two-dimensional ordination mapping of species and correlations of abundance with simple environmental variables were used to examine relationships between the individual species and this dynamic environment. The ordination indicates that species are segregated by adaptations suggestive of successional pathway and successional stage. An examination of the distribution of species abundances plotted against the environmental variables reveals few distinct relationships. The differences in species abundances and associations not related to the physical environment are hypothesized to be related to successional processes because of the attributes of the species themselves. Differences in abundances between native herbaceous species and European ruderals and between Populus and Salix species suggest that founder effects may be important.