Developments in plant colonization and succession on Surtsey during 1999–2008

Abstract

Plant immigration on Surtsey continued during 1999–2008 and 69 vascular plant species had colonized the island by 2008. That year 63 species were recorded, of which 32 had formed viable populations. Birds were considered the main agents of seed dispersal to the island, having dispersed 75% of the species, while 16% were wind dispersed and 9% by sea from 1965. Plant succession was studied in permanent plots. Barren areas were starkly distinct from a gull colony area affected by breeding seagulls from 1985. Average breeding density by plots within the gull colony was 4 nests 1000 m-2 during 2003–2008. Species richness, plant cover and biomass remained low in the barrens. Here two communities, a Honckenya peploides community on tephra sand and a gravel flats community with Silene uniflora as the indicator species, had developed. Carbon and nitrogen content of soil in barrens was very low and pH relatively high. By 2008, plant species richness in the gull colony was considerably higher than in the barrens and average plant cover and biomass was from 10 to 40 times greater. Soil within the colony area had a relatively high C and N content, and pH was lower than in the barren area. Two forb-rich grassland communities had developed within the colony. on lava, a Puccinellia distans/ Sagina procumbens community composed mainly of ruderal species, and a community with the perennial grasses Poa pratensis, Leymus arenarius and Festuca richardsonii as dominants on sand and lava. With the closing of the grassland sward, species richness had declined, reflecting developing dominance. in 2008 the forb-rich grassland of the gull colony had expanded to about 10 ha in area. it had become a foundation of an abundant invertebrate life and a small community of land birds developing on the island from 1996. Seabirds (primarily gulls) have become increasingly important in shaping and driving the ecosystem development on Surtsey through their nutrient transfer from sea to land and by dispersal of seeds to the island. Puffins have recently started breeding on the island and they are expected to affect further development of the ecosystem.