Keen of Hamar National
Nature Reserve
A Lunar Landscape
You
might feel as though you have landed on the moon when you first arrive at
the Keen of Hamar. The barren scene seems bleak and lifeless, but
appearances can be deceiving. This is a landscape in motion and nestling
in its stony ground are some of the rarest plants in Britain. To the
untrained eye there is certainly something special about the place, but
for a botanist it is heaven.
A Unique Habitat
Hamar means "rocky outcrop on the hillside". The soil
here is among the oldest and poorest in Britain and the scene probably
resembles what much of Northern Europe looked like as the ice retreated
after the last ice age some 10,000 years ago. The rock type at the Keen of
Hamar is serpentine and where it weathers in such a way to produce large
numbers of small angular fragments, it is known as `debris'. Serpentine
outcrops occur elsewhere in Unst, on the neighbouring island of Fetlar, at
the Lizard in Cornwall, on the islands of Rum and Skye, and in small areas
of Fife and Aberdeenshire. What is unique about the Keen however is the
extent of serpentine debris - one of the largest expanses in Europe.
Photo right: serpentine outcrops on the
Keen of Hamar.
A Mountain near Sea Level
Stone stripes can be found on the bare north facing
slopes of the reserve. These are formed through the sorting of stones by
size following repeated freezing and thawing of water in the soil. In
Britain this process is normally associated with high mountains such as
the Cairngorms or Helvellyn in the Lake District. But at the Keen of
Hamar, where there is little vegetation to hold the soil together, these
stone stripes occur at just 50m above sea level. These stone stripes are
currently active and may move downslope by up to a few centimetres each
year - a landscape in motion. Experiments have shown that where the ground
surface has been disturbed the stripes may reform in a single winter.
Soil Transported by
Ice
There are actually two types of `soil' found on the
reserve. The visible effect of this is quite dramatic and results in the
complex patchwork of vegetated and bare areas we see today. Much of the
site comprises bare serpentine debris and this debris is still being
produced as the forces of the weather shatter more serpentine bedrock into
tiny pieces. This can be seen on the upper slopes of the Keen. Elsewhere,
thin, stoneless, sandy soils give rise to well vegetated patches on the
lower slopes of the reserve. This heathland is typical of the vegetation
found on much of the Sheltand serpentine and is rich in flowers, grasses
and sedges. Although this soil was derived from serpentine, it did not
originate from the bedrock at the Keen but was transported to the site and
deposited there by moving ice more than 10,000 years ago - a drift
deposit.
Some Very Special Flowers
The community of flowers that are specially adapted to
life on he debris is one of the most impressive in North West Europe. A
number of species with a restricted distribution in Britain grow here
including, northern rock cress, Arabis petraea, hoary whitlow
grass, Draba incana, Norwegian sandwort, Arenaria norvegica,
and rarest of all Edmondston's chickweed, Cerastium nigrescens.
This plant was discovered in 1837 - by Thomas Edmondston of Buness, later
Professor of Botany at the Anderson University of Glasgow. Other species,
notably scurvy grass, Cochlearia offtcinalis, stone bramble,
Rubus saxatilis, thrift, Armeria maritima, and sea plantain,
Plantago maritima, show distinctive growth forms adapted to the
conditions on the Keen of Hamar.
Photographs (left to right, top to bottom): Slender St. John's Wort -
Hypericum pulchrum. This bright yellow flower can be found among healthy
areas on the reserve. It is the only representative of its family in
Shetland.
Kidney
Vetch - Anthyllis vulneraria. This species is often found close to the
coast. The colour of the flowers is very variable although those found on
the Keen are an unusual, lemon-yellow.
Hoary
Whitlow Grass - Draba incana. This species likes exposed places where it
clings to rocky outcrops, its roots deeply embedded in crevices. Look for
the tiny rosette of leaves just around the margins of the green-topped
rocky mounds that can be found on the slopes of the Keen.
Frog
Orchid - Coeloglossum viride. This inconspicuous green and red orchid is
actually quite widespread on the reserve although orchid spotters need to
get down on their hands and knees on the areas of short turf to find it.
Research On The Keen
Pegs marking fixed quadrats and transects are a
human feature of the reserve! For over 25 years scientists have been
attempting to explain why the debris habitat is so inhospitable for plant
growth and, why natural processes of succession i.e. the build up of a
soil leading eventually to complete vegetation cover have not occurred.
Various theories have been put forward including the presence of toxic
metals in the debris soil or, a lack of nutrients essential for plant
growth. These factors may still be in part responsible, but today a
shortage of water in summer is the favoured explanation. It is difficult
to imagine that water shortage could ever be a problem in Shetland.
However the coarse nature of the debris and the lie of the land means that
any rain that falls tends to run off the site. Many of the plants do show
adaptations to living in very dry conditions such as fleshy leaves,
extreme hairiness and extensive root networks.
Although
the site has certainly been grazed by farm animals in the past there is
now no grazing, other than by rabbits. A fenced corridor through the
middle of the site allows cattle to move between areas of grazing pasture.
The effects of the enrichment of the debris by a natural fertiliser,
cattle dung, can be seen here. The field adjacent to the reserve entrance
also illustrates the sensitive nature of this site. Here the debris was
fertilised and reseeded.The reserve declared in 1975, is owned by Scottish
Natural Heritage. It is situated east of the A968 north of Baltasound
(take the side road to Little Hamar).
Photo left: Edmonstons Chickweed -
Ceratium nigrescens. Discovered by local botanist Thomas Edmonston of
Buness in 1837, this plant's world distribution is restricted to the
serpentine debris on Unst. The large white flowers can be seen from June
to August.
Guidance
for visitors
In the
interests of this special place and your own safety we ask you to:
-
Leave dogs behind as they are likely to disturb the fragile habitat.
-
Not
to leave litter. It can kill or maim animals.
-
Not
to take plants or animals, only photos.
-
Not
to disturb nesting birds.
-
Take care on the cliffs.
-
Norweigan Sandwort is specially protected under the 1981 Wildlife and
Countryside Act and it is an offence to intentionally damage or destroy
the plant or to collect its flowers and seeds.
All text and
pictures copyright Scottish Natural Heritage © SNH 1999
For further
enquiries contact: Scottish Natural Heritage, Ground Floor, Stewart
Building, Alexandra Wharf, Lerwick, Shetland. ZE1 0LL. Telephone (01595)
693345.
Nature in Shetland
