1Department of Biology, University of Washington, Seattle, Washington 98195, USA
2Icelandic Institute of Natural History, Urriðaholtsstræti 6–8, P.O. Box 125, 220 Garðabær, Iceland
Received: 09 Oct 2013 – Discussion started: 10 Dec 2013
Abstract. Surtsey and Mount St. Helens are celebrated but very different volcanoes. Permanent plots allow for comparisons that reveal mechanisms that control succession and its rate and suggest general principles. We estimated rates from structure development, species composition using detrended correspondence analysis (DCA), changes in Euclidean distance (ED) of DCA vectors, and by principal components analysis (PCA) of DCA. On Surtsey, rates determined from DCA trajectory analyses decreased as follows: gull colony on lava with sand > gull colony on lava, no sand ≫ lava with sand > sand spit > block lava > tephra. On Mount St. Helens, plots on lahar deposits near woodlands were best developed. The succession rates of open meadows declined as follows: Lupinus-dominated pumice > protected ridge with Lupinus > other pumice and blasted sites > isolated lahar meadows > barren plain. Despite the prominent contrasts between the volcanoes, we found several common themes. Isolation restricted the number of colonists on Surtsey and to a lesser degree on Mount St. Helens. Nutrient input from outside the system was crucial. On Surtsey, seabirds fashioned very fertile substrates, while on Mount St. Helens wind brought a sparse nutrient rain, then Lupinus enhanced fertility to promote succession. Environmental stress limits succession in both cases. On Surtsey, bare lava, compacted tephra and infertile sands restrict development. On Mount St. Helens, exposure to wind and infertility slow succession.
Revised: 12 Feb 2014 – Accepted: 23 Feb 2014 – Published: 14 Apr 2014
del Moral, R. and Magnússon, B.: Surtsey and Mount St. Helens: a comparison of early succession rates, Biogeosciences, 11, 2099-2111, doi:10.5194/bg-11-2099-2014, 2014.