COLONIZATION OF THE LAND
How Are the Plants Studied?
At the beginning of research in Surtsey,
each new individual among higher plants was observed and its place of
discovery and growth registered on a map of the island. Each new plant
was labelled with a wooden stick and given an identification number.
The growth of the plant was measured and its flowering and seed formation
was possible while the number of individual plants was small, but when
the plants started to disperse their seeds in Surtsey and the rate of
reproduction increased, it became impossible to label each individual
and observe its development. Instead, permanent plots were set up in
different habitats and locations on the island in order to follow plant
succession. In addition, changes in the soil and invertebrate fauna
in the plots are observed. Furthermore, each summer the island is combed
for new pioneers, and the status of all species growing outside the
permanent plots is updated. This has given a clear picture of the colonization
of higher plants and the increase in the number of species on Surtsey.
Coastal Species Were the First
In the first two decades, the sands and
lava of Surtsey were quite barren and soil development was poor. Few
species are adapted to such conditions and able to grow and reproduce
under them. Shore plants that grow on sandy beaches and in windblown
sand are adapted to nutrient-poor soils and can survive in severe conditions.
Such plants were the first pioneers to colonize Surtsey and were characteristic
of the vegetation during the first decades, along with the mosses and
lichens that were found early on the island. This first period of plant
history in Surtsey was therefore characterized by species adapted to
dispersal by the sea or wind and capable of growing and surviving under
first higher plant species found in Surtsey was sea rocket (Cakile
arctica) in 1965. It was also found there the following year along
with sea lyme grass (Leymus arenarius). In 1967 these species
were joined by oyster plant (Mertensia maritima) and sea sandwort
(Honkenya peploides). In the late summer of that year the sea
rocket flowered and was the first species to reach that stage. However,
in these first years no higher plants survived overwinter in Surtsey,
as they were either buried in the sand or washed away by the winter
The first higher plant to survive over
winter was the sea sandwort. The species overlived in the winter of
1968-69, and it has done very well since then. Only a few years passed
before it had flowered and formed seeds. The first seeding taking place
in 1971, which his was a turning point in the dispersal of this plant,
and consequently it´s spread all over the island as the years
Sea sandwort is now by far the most common
higher plant species on Surtsey, growing everywhere that any pumice
and sand can be found. The number of plants is most likely several million,
and the largest ones have formed hummock-like patches with an area of
several square meters. Sea sandwort has a well-developed fibre root
system growing deep into the sand and beyond the plant surface above
ground. In this way it can utilize nutrients from a large area to grow
took sea lyme grass and oyster plant a longer time to reach the flowering
and seeding stages. Consequently, these plants began spreading and forming
populations later than the sea sandwort. It was in the years 1977 -
1979 that sea lyme grass and oyster plant started seeding and spreading
throughout the sands and pumices. Sea lyme grass is a hardier species
and is now one of the most common species on the island. It has formed
several sand dunes decorated with sea sandwort and oyster plant. In
this manner, there has developed on Surtsey a community of shore plants
quite similar to the vegetation on sandy shores of Iceland. The annual
species sea rocket and smoothish orache (Atriplex longipes) have occasionally
been found on the northern ness, but they have not succeeded in establishing
stable populations on the island.
During the period 1975-1985, following
the colonization by the shore plants, very few new species were added
to the young flora of Surtsey, and the succession slowed down (graph).
Plant Succession with Increased Gull Breeding on Surtsey
The first birds to nest in Surtsey were
the fulmar (Fulmarus glacialis) and the black guillemot (Cepphus
grylle) in 1970. In 1974, they were joined by the great black-backed
gull (Larus marinus), in 1975 by the kittiwake (Rissa tridactyla)
and in 1981 by the herring gull (Larus argentatus). Breeding
birds were nevertheless very few to begin with, and their influence
on the vegetation development was rather limited. In 1986, a lesser
black-backed gull (Larus fuscus) was discovered breeding on
Surtsey for the first time. At this point in time, a gull colony was
beginning to develop on the lava on the southern part of the island,
where 10 lesser black-backed gull and herring gull nests were found.
A sharp increase in the breeding population occurred over the next few
years, and the dense breeding population that had soon developed grew
larger each year. In 1990, the number of breeding pairs had risen to
200. By that time lesser black-backed gulls, herring gulls and great
black-backed gulls were found in the colony.
population explosion in the gull colony on Surtsey after 1986 was accompanied
by a new wave in the colonization of higher plants and the succession
of vegetation. The stagnation that had characterized previous years
was broken. A number of new species began to colonize the island, and
most of them were discovered within the gull colony. It is likely that
many of the species were dispersed to the island by the gulls. In the
period 1985-1995, the number of higher plant species on Surtsey grew
from 21 to 44. In recent years the increase in number has slowed down.
In the summer of 2004, 60 species of higher plants had been found on
Surtsey of which 54 had living representatives on the island that year.
This shows how the gull invasion has affected plant colonization and
survival on Surtsey (graph).
In the gull colony, not only did the species
increase in number but the vegetation also became denser due to the
fertilizing effects of the birds. In only a few years, the black pumices
and lava sands changed into a lush grassland and forb community. By
the year 2004, the breeding area on the southern part of the island
had expanded to about 10 hectares.
Comparison of Vegetation outside
and inside Gull Colony
The succession of vegetation has been
observed closely, in permanent plots both outside and inside the gull
colony, since 1990. Changes have been slow outside the colony, the most
interesting being that species characteristic of gravel plains, especially
northern rock cress (Cardaminopsis petraea), sea campion (Silene
uniflora) and thrift (Armeria maritima), have been found
and are beginning to spread over the island in areas formerly colonized
by the sea sandwort, lyme grass and oyster plant. In permanent plots
(100 m²) outside the gull colony, the number of plant species recorded
in the summer of 2002 ranged from 1-5, and the total plant cover did
not reach 30% in any of them. Inside the gull colony there were, on
the other hand, up to 10 different species in each plot, and there was
a continuous plant cover in some of them.
In sandy areas inside the colony, the
most abundant species in the vegetation are the sea sandwort, sea lyme
grass, annual meadow grass (Poa annua), common meadow grass
(Poa pratensis), common chickweed (Stellaria media),
common mouse-ear (Cerastium fontanum) and the sea mayweed (Matricaria
maritima), while in the lava the reflexed saltmarsh grass (Puccinellia
distans), scurvy grass (Cochlearia officinalis) and procumbent
pearlwort (Sagina procumbens) are most prominent. Arctic fescue
(Festuca richardsonii) has been found at several sites where
it has formed homogenous patches that increase in size from year to
year. These patches are similar to grass swards of Arctic fescue, which
dominate in many bird colonies of the neighbouring islands.
Northern green orchid (Platenthera
hyperborea) and lady’s bedstraw (Galium verum) were
found for the first time on Surtsey in the summer of 2003 (see
article here, in Icelandic), and both these plants were in lush
vegetation in the gull colony. They are examples of species that colonize
land where vegetation has been developing for a while. The same is true
of a few species of grassland mosses that have begun to colonize the
gull colony on Surtsey. This confirms that plant succession on Surtsey
is no longer in the primary stage.
Late Invasion by Willows
Dwarf willow (Salix herbacea)
was discovered on Surtsey in 1995 and was the first willow species to
colonize the island. A few individuals of this species have been found,
and in recent years both tea-leaved willow (Salix phylicifolia)
and woolly willow (Salix lanata) have been discovered on the
island. The willow plants have been found both inside and outside the
gull colony. It is likely that the seeds of all these species were dispersed
by wind to Surtsey in the early days, but that conditions for their
growth and development were not favourable until during the last decade.
The improved soil conditions following the gull colonization are probably
the main reason for this invasion of willows on Surtsey.
Future Development of Vegetation
number of higher plants growing on Surtsey has become considerably higher
than of most of the neighbouring Vestmannaeyjar (Westman Islands), which
are considerably smaller in size. These islands host 2-30 species, and
there is a close relationship between island size and species richness.
On Heimaey, which is the largest of the Vestmannaeyjar there are about
150 species of higher plants. The island is seven times the area of
The number of species on Surtsey will
continue to rise during coming decades. It is unlikely, however, that
the number will ever reach 100. In the future, Surtsey will continue
to erode and shrink, with a consequent loss of habitats and species.
Surtsey will become similar to its small neighbours, Geirfuglasker and
Súlnasker, which have less than 10 plant species in their flora.
a slideshow of higher plants on Surtsey
Fririksson, Borg■ˇr Magn˙sson - email@example.com)
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