Vegetation succession on Surtsey, Iceland, during 1990-1998 under the influence of breeding gulls

Abstract

Vegetation successio~la nd soil clevelop~lle~wlte re studied on Sui-tse): in 22 permanent plots that were set 11p in 1990 to 1995. The plots were on sand or lava substrate and outside or inside a gull coloily that started forming on the islalld in 1986. The formation of the colo~lyw as followed by enhancement of plant cover in the breeding area and a sllarp rise in rate of colo~~izatiooifl plant species not foui~cpl reviously on the island. T~veaty species of vascular plants were recorded within the plots in 1998, when a total of 47 species was founcl on the whole islancl. Plots outside the guI1 colony had on average 2 species and 6% plant cove^: Honlrt??ipri pe/)Zoirlc~I vas the lllost PI-ominent species in the saild plots but Si~gi??pnr ocrcnlbens in the lava plots. Inside the gull colony 9 species were found on average in each plot ancl total cover was 72%. In sand plots inside the colo~lyH onke1~)1(/1~ eo/~loirlPs,o c~r r,i,li.z~rca nd Slcllrtria rnr?rlin werc the dominant species, but Piicciiiellin riisti~17as ncl Cocl~ler~'roif[/~ir ilzrrlis in the lava plots. The soil outside the cololly was high in pH (7.5) ancl low in total C (~0.1%)I.n side the cololly the soil pH (6.4) had decreased and total C (1.1%) increased. Changes in vegetatio~l cover and species richness have been minor in plots outside thc gull colony during the st~~cplyer iocl and the clomi~la~slpt ecics Ho7zkc/zjlrc pe/)loirles appears to have f~lllyc olo~~izetchle sand areas. Most of the species of these areas are pere~lllialsw it11 clollal growth. M'ithin the gull colony plant cover and species richness have, on the other hand, i~lcresecln vo to th1-eefolcl. The vegetation of the gull cololly is characterized by perennial and a~liluals pecies aclaptecl to disturbed and nutrient-rich habitats. Most of the species are foulld in bird colo~lieso n neighbouring islands.