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Oxford Ragwort Senecio squalidus |
Recently I have become aware of
PlantTracker
which has been set up by the Environment Agency, the Nature Locator
team at Bristol University and the Centre for Ecology and Hydrology.
They are asking for help from the public to track down non-native
species that are a threat to our native wildlife. It is well known how
species such as
Rhododendron ponticum,
Fallopia japonica (Japanese Knotweed) and
Crassula helmsii
(New Zealand Pigmyweed) have become unwelcome aliens in our Country.
There is a website and an app for use on smartphones to help locate the
plants. The results are already proving to be of help to them and to the
BSBI in identifying key risk sites for further invasion problems.
I well remember the excitement back in the 1970s that the late Dr Francis Rose showed when he first found
Crassula helmsii in
a small pond adjacent to Hatchet Pond in the New Forest. His excitement
was caused by the fact that his initial identification of it was
Elatine hydropiper,
a very rare species that he had never seen before. Further research
however put him right, and the truth was that he had had his first
encounter with a most unpleasant alien. It did not take long for the
whole of the bottom of that pond to be a one species carpet of
Crassula helmsii with some important species crowded out completely.
The first occurrence of
Crassula helmsii in the New Forest was recorded by the late and very able, deaf botanist Paul Bowman. His notebook showed that having found
Crassula helmsii
nearby, he then drove to Hatchet Pond. Circumstantial evidence suggests
very strongly that a small piece of the plant may well have attached
itself to his boot. This shows just what an invasive threat this species
must be. The original source of the invasion is thought to have been an
aquarist supply shop in Essex.
The story of Oxford Ragwort
Senecio squalidus
is fascinating. This species is now ubiquitous on the tops of walls and
throughout Britain’s railway system. It is now completely taken for
granted as part of the British flora. It is called Oxford Ragwort
because it was grown in Oxford Botanic Gardens in the late 17th century
having been collected from volcanic cinders on the slopes of Mount Etna.
It was a small hop from its flower bed in Oxford to the walls of the
Botanic Garden from whence it found the walls in the rest of the City
and, from 1844, the cinders on the early railway tracks passing through
the town. In no time at all, it had established itself throughout
Britain on its fast expanding railway network.
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Rhododendron removed from one ownership but dense in a
neighbouring one in Sussex |
Another species Canadian Pondweed,
Elodea canadensis
was a terrible invasive menace in the past, but now seems to have
settled itself relatively comfortably into the ecology of aquatic
habitats. One of the great problems with invasive species is that they
have no predators, species that feed on them or diseases that keep them
in check in their new home. The very attractive bug
Graphocephala fennahi was introduced into Britain in the 1930s from America. This species
feed on rhododendron, and it appears possible that it also spreads a
fungus that attacks it. Japanese Knotweed seems to be a species that is
extremely difficult to eradicate, and once established creates a habitat
that is devoid of pretty well all other species of wildlife. It creates
such a dense cover that other photosynthetic organisms cannot establish
themselves beneath it.
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Harlequin Ladybird |
As everyone knows, unwanted, and invasive aliens are
not restricted to the plant world. Grey squirrels, mink and more
recently harlequin ladybirds are all species that have had a savage
effect on our native fauna. It is interesting that bluebells are rather
rare in Europe, and the wonderful and ebullient spectacle of the British
bluebell wood does not exist there. The reason for this is that wild
boar are native in Europe, and control bluebells by digging them up, and
eating them. Is it possible that bluebells became an invasive species
when the wild boar finally became extinct in Britain? Is it possible
that this acknowledged aspect of our wildlife heritage will be
threatened by wild boar becoming once more established here?
Interestingly
Cyclamen hederifolium with its English name
Sowbread has not become invasive in our woodlands although it is grown
extensively, and does very well as a garden plant. Where established, it
can provide a fine spring show on hedge banks. In Europe, woodland can
be “ploughed” by wild boar seeking the corms of wild cyclamen.
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Himalayan Balsam Impatiens glandulifera |
There has been encouragement from conservationists to
provide wildlife corridors to encourage the spread of wildlife.
Unfortunately it is the aggressive, non native aliens that benefit from
most habitat corridors. One only has to see the spread of
Impatiens glandulifera
Himalayan Balsam throughout our river and canal system to see how
beneficial wildlife corridors can be to alien species. The same is true
of our railway system and the spread of Oxford Ragwort. Most native
species such as dormice, bats and badgers do not spread their range
along wildlife corridors although some may use corridors such as
hedgerows to find forage. It would be wonderful if otters were able to
return to our river system as rapidly as mink did and it is heartening
to see how many have returned already. A much better way to encourage
an increase in native wildlife is to increase the acreage of our best,
existing wildlife habitats. As mentioned in my first blog, many of the
lichens that are used for estimating the age and ecological continuity
of woodland are probably dispersed in the digestive systems of molluscs.
In the New Forest, Burley Old Inclosure which was newly planted around
1700 has developed both as habitat and in its lichen flora to compare
favourably with neighbouring native, ancient and ornamental woodland.
Discouraging
the spread of aliens using non-native biological control may be fraught
with difficulty. There are examples of non-native predators becoming a
greater threat than the species they were designed to control. Where
successful, such control may be very effective, but extreme caution is
required before such biological control is implemented. Most
conservationists shy away from the use of chemical control, however it
seems that chemical methods are about the only armament available for
the control of Japanese Knotweed. Invasive species are not confined to
land, they can also cause havoc in marine habitat around our coast. The
slipper limpet is a case in point as is Japweed
Sargassum muticum
which became established on the Isle of Wight in the early 1970s. It
has now spread throughout western Britain as far north as south western
Scotland, and is established in Ireland. In Britain, its long strands
grow to the exclusion of all native marine algae where it has become
established. Control of this menace was started too late for it to be
very effective.
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Martagon Lily Lilium martagon |
Finally, the question of whether a species is native
or introduced can be fraught with difficulty. While the date in which
most became established can be easily found, there can be arguments for
the native status of species that are universally thought of as being
introduced. Of native species, smooth snake has some doubt cast upon its
native status while the late Dr Francis Rose argued strongly that there
was a case for the Martagon Lily
Lilium martagon being native.
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