Distance and environmental difference in alpine plant communities

Abstract

Differences in plant communities are a response to the abiotic environment, species interactions, and dispersal. The role of geographic distance relative to the abiotic environment is explored for alpine tundra vegetation from 319 plots of four regions along the Rocky Mountain cordillera in the USA. The site by species data were ordinated using nonmetric multidimensional scaling to produce dependent variables for use in best-subsets regression. For independent variables, observations of local topography and microtopography were used as environmental indicators. Two methods of including distance in studies of vegetation and environment are used and contrasted. The relative importance of geographic distance in accounting for the pattern of alpine tundra similarity indicates that location is a factor in plant community composition. Mantel tests provide direct correlations between difference and distance but have known weaknesses. Moran spatial eigenvectors used in regression based approaches have greater geographic specificity, but require another step, ordination, in creating a vegetation variable. While the spatial eigenvectors are generally preferable, where species–environment relations are weak, as seems to be the case for the alpine sites studied here, the fewer abstractions of the Mantel test may be useful.

Keywords:

• Beta diversity
• biogeography
• Mantel correlation
• Moran eigenvectors
• tundra

Acknowledgments

Help with botany was provided by Jen Asebrook and Jen Hintz of Calypso Ecological, LLC. Kevin Jacks assisted in the field and Mitch Kinney organized and prepared the data. Logistical support was afforded by Bill Bowman and Roger Patison. This material is based on work while GPM served at the National Science Foundation. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the USGS; any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US government.