Co-ordinating Editor: Dr. Kerry Woods.
Primary succession trajectories on a barren plain, Mount St. Helens, Washington
Article first published online: 20 APR 2010
© 2010 International Association for Vegetation Science
Journal of Vegetation Science
Volume 21, Issue 5, pages 857–867, October 2010
How to Cite
Del Moral, R., Saura, J. M. and Emenegger, J. N. (2010), Primary succession trajectories on a barren plain, Mount St. Helens, Washington. Journal of Vegetation Science, 21: 857–867. doi: 10.1111/j.1654-1103.2010.01189.x
- Issue published online: 1 SEP 2010
- Article first published online: 20 APR 2010
- Received 9 December 2009;Accepted 14 March 2010.
- Community assembly;
- Permanent plots;
- Rate of succession;
- Redundancy analysis;
- Stochastic assembly;
- Succession network
Questions: Have predictable relationships between environmental variables and vegetation developed in primary succession following a volcanic eruption? Has the rate of succession changed? Have vegetation trajectories converged or diverged?
Location: The Abraham Plain of Mount St. Helens, Washington, USA (46°12′42″N, 122°08′27″W, elevation 1360 m), was sterilized in 1980 by a blast, scoured by lahars and buried by pumice.
Method: We monitored 400 100 m2 contiguous permanent plots annually (1988–2008), and classified each plot from every year into ten community types (CTs). We characterized the terrain by topography and surface features. Redundancy analysis assessed relationships between vegetation and possible explanatory variables, which included sample location. We used detrended correspondence analysis (DCA) to assess successional rates and trends.
Results: Relationships between species composition and explanatory variables were only significant after 1996, when position and presence of rills became significant. By 2006, explained variation remained low (13%) but significant. Species accumulated slowly, restricted by stress and isolation. Changes in mean DCA position slowed. Composition shifted from pioneer to persistent species and vegetation became more stable with time. Species accumulated for two decades and then stabilized, while cover has continued to increase. Diversity increased and then declined slightly as dominance developed and pioneer species became less common.
Conclusions: We demonstrate weak but increasingly predictable trends in species composition using environmental variables. The rate of succession slowed and trajectories formed a reticulate network of transitions dominated by divergence. Convergence was not evident because vegetation responded distinctively to minor topographic features that allowed alternative stable communities to develop.