Vascular plant colonisation, distribution and vegetation development on Surtsey during 1965–2015

Abstract

Since Surtsey was formed in 1963–1967, colonisation of vascular plants has been recorded by locating the f irst colonists of each species within a 1 ha (100x100 m) quadrat grid system of the island. The abundance of individual vascular plant species was further recorded within the grid in 1996-1997, 2005-2006, and 2014-2015 using a three graded abundance scale from rare to common. During 1965–2015, a total of 74 vascular plant species were found on Surtsey. The colonisation was considerable between 1965–1979 followed by a stagnation period. After the establishment of a dense seagull colony on the southern part of the island in 1986, colonisation increased greatly and peaked between 1992–1995. The colonisation differed greatly between surface types, being highest on sandy lava and barren lava, relatively low on eolian sand and coastal sediments, and none on palagonite tuff. By classification and ordination six main vegetations types were identified over the period 1996–2015, forming a gradient from scattered, species poor pioneer vegetation to a dense, lush vegetation developed under by high nutrient input from breeding seagulls. Over this period major vegetation changes occurred. Areas with pioneer vegetation have greatly decreased, while areas with Honckenya and gravel flat vegetation, and forb rich grassland have increased. The number of species per ha increased on average from 4.8 to 7.2 and 10.4 in the years 19961997, 2005-2006, 2014-2015 respectively. Despite the great influence of seabirds within their breeding colony, most of the island still has sparse vegetation cover. The colonising species differed greatly in their rate of dispersal. Species with the greatest rate were Honckenya peploides, Poa annua and Silene uniflora, followed by Sagina procumbens, Puccinellia coarctata, Cerastium fontanum, Arabidopsis petraea, Leymus arenarius and Rumex acetosella. They are either pioneers and/or ruderals and are common on the mainland of Iceland, where they grow in sparsely covered, rocky or sandy areas or on land that has been disturbed.