Multiscale Factors Control Community and Species Distribution in Mountain Peatlands

We studied the vegetation of 166 fens in Yellowstone National Park, USA, to determine the relationship between species distribution in mountain peatlands and regional-, landscape-, and local-scale environmental variables. Plant commun- ities were identified through hierarchical agglomerative cluster analysis, patterns in species distribution were explored using nonmetric multidimensional scaling, and the relative importance of variables was assessed though partial canonical corre- spondence analysis. Five major bedrock types influenced groundwater feeding fens: three volcanic types, a glacial till com- plex, and rock altered by acidic geothermal activity. Ionic concentrations generally increased with pH, but acidic geothermal fens had very low pH and high electrical conductivity. Bryophyte distribution was controlled by groundwater chemistry, while vascular plants responded to a broader range of variables. When partitioned by spatial scale, landscape variables ac- counted for >60% of the variation explained. When partitioned categorically, geochemical and topographic variables were more important than geographic factors. For fens in mountainous regions, the primary gradient is site-level water chemistry, which is strongly linked to regional bedrock geology. Site- and stand-level topography represent a secondary gradient. Most mountain fens fit within the established poor–rich gradient; however, geochemical acid production creates a distinct category outside the conventional paradigm.