Abstract
Abstract. Plant colonization and succession on the volcanic island of Surtsey, formed in 1963, have been closely followed. In 2013, a total of 69 vascular plant species had been discovered on the island; of these, 59 were present and 39 had established viable populations. Surtsey had more than twice the species of any of the comparable neighbouring islands, and all of their common species had established on Surtsey. The first colonizers were dispersed by sea, but, after 1985, bird dispersal became the principal pathway with the formation of a seagull colony on the island and consequent site amelioration. This allowed wind-dispersed species to establish after 1990. Since 2007, there has been a net loss of species on the island. A study of plant succession, soil formation and invertebrate communities in permanent plots on Surtsey and on two older neighbouring islands (plants and soil) has revealed that seabirds, through their transfer of nutrients from sea to land, are major drivers of development of these ecosystems. In the area impacted by seagulls, dense grassland swards have developed and plant cover, species richness, diversity, plant biomass and soil carbon become significantly higher than in low-impact areas, which remained relatively barren. A similar difference was found for the invertebrate fauna. After 2000, the vegetation of the oldest part of the seagull colony became increasingly dominated by long-lived, rhizomatous grasses (Festuca, Poa, Leymus) with a decline in species richness and diversity. Old grasslands of the neighbouring islands Elliđaey (puffin colony, high nutrient input) and Heimaey (no seabirds, low nutrient input) contrasted sharply. The puffin grassland of Elliđaey was very dense and species-poor. It was dominated by Festuca and Poa, and very similar to the seagull grassland developing on Surtsey. The Heimaey grassland was significantly higher in species richness and diversity, and had a more even cover of dominants (Festuca/Agrostis/Ranunculus). We forecast that, with continued erosion of Surtsey, loss of habitats and increasing impact from seabirds a lush, species-poor grassland will develop and persist, as on the old neighbouring islands.
Highlights
The frequent volcanic eruptions in Iceland cause regular disturbance and ecosystem regression (Arnalds, 2013)
Surtsey had more than twice the species of any of the comparable neighbouring islands, and all of their common species had established on Surtsey
The plant colonization curve for the island over the first 50 years can be divided into four main periods (Fig. 3)
Summary
The frequent volcanic eruptions in Iceland cause regular disturbance and ecosystem regression (Arnalds, 2013). In the more severe eruptions, existing biota and ecosystems are lost and new surfaces created; thereafter, colonization and primary succession commence. The 1963 submarine eruption and birth of Surtsey island off the southern coast of Iceland was, a surprise. The volcanic origin of the Vestmannaeyjar islands was known, but the previous eruptions in the system had occurred over 5000 yr ago (Sigurðsson and Jakobsson, 2009). The Surtsey eruption, soon followed by the Heimaey eruption in 1973, set a new focus on the islands and extensive geological and biological research was initiated (Lindroth et al, 1973; Friðriksson, 1975; Friðriksson and Magnússon, 1992; Jakobsson et al, 2007; Svavarsdóttir and Walker, 2009). A few volcanic islands have recently emerged, including Anak Krakatau (1927) in Indonesia, Tuluman Island (1953)
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