Náttúrufræðingurinn - 2023, Blaðsíða 22

árum og einnig hafa sést merki um að
hann sé tekinn að þreifa fyrir sér uppi í
graslendinu. Miklar líkur eru á að lunda
stórfjölgi í eynni og að hann verði þar
einkennisfugl þegar tímar líða. Ásamt
fýl, máfum og fleiri sjófuglum má búast
við að hann viðhaldi þar gróskumiklu
graslendi líkt og í öðrum úteyjum Vest-
mannaeyjaklasans. Þær sýna glöggt hvað
bíður Surtseyjar og lífríkis hennar.
SUMMARY
Surtsey Volcanic Island At Sixty:
Vascular Plant Colonization and
Ecosystem Development
Surtsey volcanic island rose out of the
sea in the fall of 1963, formed in a vol-
canic eruption that lasted into the sum-
mer of 1967. It is the youngest island of
the Vestmannaeyjar island archipelago
off the south coast of Iceland. From
1964, colonization of life and ecosystem
development has been studied on Surts-
ey. The colonization of vascular plants
has been studied in greatest detail and
annual records from the first finding
in 1965 exist. In 2022 a total of 78 spe-
cies had been recorded on the island, of
those 63 species had living individuals
and over 40 species had formed viable
populations. Shore species were the
first colonizers of the island, their seeds
washed by the sea upon the northern
shores. They are adapted to sandy, infer-
tile substrates and able to establish un-
der harsh conditions. Most of the shore
species were successful and started
spreading within the next few years.
Following their establishment plant
colonization slowed markedly down. In
1985, a dense breeding colony of seagulls
(Lesser black-backed gull, Herring gull
and Great black-backed gull) started to
form on the southern part of the island.
It was followed by a sharp increase in
plant colonization. The birds dispersed
new plant species to the island and im-
proved soil conditions through their nu-
trient transfer from sea to land. Within
the breeding area plant growth was
greatly enhanced. This second wave of
colonization continued for about two
decades when it slowed down. How-
ever, colonization by new vascular plant
species is still ongoing and the flora of
Surtsey has become considerably richer
than that of the other but smaller neigh-
bouring islands. In the later years, the
number of wind-dispersed species has
increased considerably. They are more
nutrient demanding and some of them
need fungal symbionts for establish-
ing. These conditions and amelioration
were brought about by the breeding
seabirds (gulls and fulmars) upon the
island. Our studies indicate that about
10% of the current vascular plant flora
was dispersed by the sea to the island,
70% by birds and 20% by wind. All
but few of the plant species of Surtsey
are found on the other Vestmanna-
eyjar islands, the others on the mainland
of Iceland.
Since 1990, plant succession has been
studied in permanent vegetation plots
on the island. The study has revealed
a distinct difference between areas af-
fected by the seagulls and those where
their impacts are limited. Plant growth
and succession has been determined
by nutrient supply, mainly nitrogen
and phosphorous. Seagulls and fulmars
breeding upon the island transport nu-
trients from the sea to their colonies
and greatly enrich the soil. Within
their breeding grounds a dense, lush
grassland has formed, expanding from
year to year. It has become increasingly
dominated by the long-lived rhizoma-
tous grass species Festuca richardsonii,
Poa pratensis and Leymus arenarius
along with the herbs Stellaria media
and Tripleurospermum maritimum, out-
competing smaller ruderal species. The
vegetation of these areas has now strong
affinities with vegetation of bird colo-
nies of the older, neighbouring islands.
Besides the greening of Surtsey by the
seabirds there are indications that grey
seals breeding on the northern, lowland
spit have enhanced vegetation growth
in their hauling-out area. Vegetation of
areas on Surtsey that are little affected
by seabirds or seals is still very sparse.
However, their vegetation cover and
species richness is gradually increasing.
Their characteristic species are Honck-
enya peploides, Leymus arenarius, Silene
maritima, Rumex acetosella and Arabi-
dopsis petraea.
The increased breeding of seabirds
on the island and transfer of nutri-
ents from sea to land was followed by
a jump in ecosystem development on
the island. In the expanding and lusher
grassland vegetation, invertebrate life
became richer and more diverse. In
1996, the first land bird, snow bunting
feeding its young on insects, was found
breeding on the island. Few years later
the insectivorous passerine species,
meadow pipit and white wagtail, also
started breeding. In 2002, a pair of
greylag geese bred on the island, feed-
ing within the grassland area. A raven
started breeding on the island in 2006,
sitting at the top of the food chain.
The erosion of Surtsey by the ocean
continues. In 2021, more than half of the
island had disappeared. Within the com-
ing decades and centuries, it will take
the shape and size of the neighbouring
islands and its biota will become alike.
A decline will occur; habitats on Surtsey
will be lost along with many species. It
is probable that puffin, currently found
in limited numbers in the sea cliffs, will
invade the expanding grassland of Surt-
sey and form a large breeding colony.
This will have profound effects on suc-
cession and ecosystem processes on the
island as within their colonies on the
other Vestmannaeyjar islands.
Náttúrufræðingurinn
22
Ritrýnd grein / Peer reviewed