Invasive non-native species: attack of the aliens
From green parakeets to grey squirrels, and tree fungi to water weeds,
invasive non-native species are driving many British plants and animals to the
brink of extinction
'Grey squirrels are loved and detested in equal measure': the species
has caused the extinction of red squirrels across much of Britain.
There is a war going on in the parks, gardens, ponds, rivers and
greenhouses of Britain. At stake is the future of the country's native flora
and fauna. This time it's not just under threat from the usual foes - lorry
parks and a tendency to pave over front gardens - but from the 2,000-plus
non-native species of animals and plants that are estimated to have found their
way here.
Not all are deadly invaders. Some non- natives, such as the horse
chestnut (origin Asia), even become pillars of the community; but some can
wreak havoc, crowding out precious native species, spreading parasites,
stealing food sources and blanketing waterways, choking the life out of native
aquatic plants with their tendrils.
This march of invasive species - moving from the environment where they
evolved to ones where they did not - is a worldwide issue. If it were flu, we'd
probably call it a global pandemic. Scientists now take it so seriously that
the UN's Millennium Ecosystems Assessment gave invasive species joint top
billing along with climate change when it came to threats against biodiversity.
This is not an issue to be trifled with.
One of the many titanic battles against invasive species is currently
being fought at Breamore Marsh in the New Forest. The marsh, a Site of Specific
Scientific Interest, is the kind of place ecologists and botanists make
pilgrimages to. In August 2009, botanist Clive Chatters went there to monitor a
rare native plant and came back with a sample of something altogether more
disturbing.
"He said to me that he had a nasty feeling it was from a small
patch of Creeping Water Primrose," recalls his wife Catherine, who just
happens to be the non-native plants officer for the New Forest. By the time it
had been confirmed and Catherine got down there herself it was the beginning of
October. "It had spread so far across the pond that I initially thought we
must have the wrong site. I couldn't believe the rate of spread. It was horrific."
At Breamore there is concern that an outflow from the pond could
potentially allow fragments of the invasive plant into the nearby river Avon,
which is why a team of volunteers is periodically to be seen waste deep in the
cold, murky water, painstakingly pulling out the tendrils by hand. On one
November day alone they extracted 40 bags of the stuff.
Trevor Renals, the senior technical advisor for invasive species at the
UK Environment Agency, shows me a picture of a worst-case scenario in Limoges,
France. The water looks as if it's covered in the fake plastic grass butchers
often use as a display backdrop. Then there are those tell-tale yellow flowers.
It may look quite pretty, but the reality is grim. There are currently
13 sites across the UK trying to contain Creeping Water Primrose. The wildlife
officer tells me they are determined that "it will not become the next
Japanese knotweed". He almost shudders at the thought that it could become
as much of a pest as Britain's most invasive non-native plant.
At the University of Hull's department of biological sciences Dr Darren Evans
fishes a couple of large signal crayfish out of his freezer. "These are
very interesting to us in our department," he says, in the manner of a
police inspector leading an enquiry. With their distinctive red claws on the
underside and white patches on the surface, these crayfish have become the
scourge of the waterways, and are spreading across most of Britain. "We
have a long tradition of researching the marine and aquatic system, and
these are a huge issue."
His colleague Thomas Breithaupt, who works specifically on crayfish, has
found up to 20 signal crayfish per square metre in some areas. "At those
concentrations they will outcompete all other species. But before we can really
have any meaningful conservation action we need to know what the current
distribution is."
Trevor Renals tells me that when he walks around garden centres, he
holds his head in his hands. Under pressure from horticultural retailers,
successive governments have shied away from banning invasive species,
preferring voluntary schemes such as Plantlife (plantlife.org.uk), a website
which advises gardeners and those in the horticulture trade how to deal with
and avoid them. "To be fair to nursery owners," says Renals,
"there's a large range of plants that aren't problematic at all. But you
do see contaminating compost and fragments of invasive plants hitchhiking on
roots."
We can't, however, pin the rise of invasive species on a contemporary
fondness for more exotic foliage. As biologist and natural-history TV presenter
Mike Dilger makes clear, our invasive-species problem has arrived courtesy of
many carriers. "If you were looking for the poster child of the invasive
species you might choose the Muntjac. It was introduced from south China by the
Duke of Bedford to his estate at the turn of the century and now it appears to
be causing problems. Then there's the American mink, which was brought over for
fur farming. You might say that was a bad idea in the first place, but when the
protestors cut the fence to free the mink it was a form of ecological genocide.
In the British countryside they have no natural predator. And what about the
ruddy duck?" What about it, I ask. "It's now subject to an
eradication programme before it wipes out the native white-headed duck."
Add to this roll call the various vanity projects by landed gentry, the
collection escapees, the farmed fish which escape from cages damaged in storms,
the abandoned pets (such as terrapins and goldfish) put into rivers, and the
general flora and fauna ferried about on coats and on lorry tyres through
21st-century living, and the rise of invasives is really no surprise.
As a nation our reaction to their appearance can be unpredictable. Some
we love, some we hate and some people continue to plant Japanese knotweed.
"It is fascinating," agrees Dilger. "There are some
amazing niche plants that people have brought in which do no harm at all - in
Haringey for example there's a Greek dock growing. Those sort of non-natives
have huge value as biological curios. Then you have a species such as the
ring-necked parakeet. At first we all loved the bright flash of green in London
parks, but now there's a worry that they're pushing out native birds. They've
been too successful and public opinion is turning against them. Like a lot
of biologists, I'm not a huge fan of alien species because of the impact
on native wildlife and the negative implications for biodiversity
overall."
In 2008, the UK set up a non-native species secretariat. Sightings and
alert emails are picked up by Dr Helen Roy, senior scientist at the NERC Centre
for Ecology & Hydrology. They are most often from people concerned that
they've spotted the Asian hornet and the killer shrimp - both on serious alert.
"Thankfully it's usually a case of mistaken identity," says Roy.
"Especially with the hornet, which often turns out to be of the European
variety." But every one must be checked out.
In her spare time, Roy is the volunteer co-ordinator for the National
Ladybird Survey, which includes mapping the non-native invasive Harlequin
ladybird. "This is a brilliant sighting," she says, showing me a
picture of a pupa that's been sent in. To my eyes, it just looks like a
ladybird pupa, but to Roy it's a treasure trove of important information.
"You can see it has a parasitic fly on it, a scuttle fly. So now we
know not only the species but can record the ladybird parasite, too. We see a
parasite that usually attacks a native ladybird switching to a Harlequin.
It's evolution in action. There is just no such thing as too much information
on invasive species."
Increased information also helps scientists make decisions on where to
tackle an invasive species, or whether they will flourish happily and add to
the ecology. Even Roy has her non-native favourites. "I have soft spots
for the Bryony ladybird, and the cream-streaked ladybird which came here in the
1930s," she admits. "It's very slow to spread and causes no notable
problems. In fact, large numbers of these new species aren't causing a problem.
It's about determining the threat level. We may have lots of information on the
native ecology of a species, but not on it within its invaded range. We
don't know what threat they pose until we have information on what they are
eating or their interactions with other species. Are they being confined to
urban areas, how commonly are they found in the wider countryside? When we have
a better idea we can ask more detailed questions about what they're doing
in those localities."
Trevor Renals emphasises that it's not just about guarding borders.
"The cost of repairing the damage from non-native invasives can rise
exponentially," he says. "With some species you could get to the
point where it's not feasible to control them anymore. What we need to rely on
to make decisions is good recording."
And this is the point where we all pitch in. The scientists monitoring
invasive species want your data. "What we don't yet have is a big enough
programme to record invasive species so that we can map them," says Darren
Evans. Along with Dr Michael Pocock of the NERC Centre for Ecology &
Hydrology he rolled out a project, Conker Tree Science, last year to use
citizen science (namely you, me and our mobile phones) to begin cataloguing the
spread of the horse chestnut leaf miner bug across the UK. His goal now is to
generate data that can be used in a scientific journal and to progress research
of non-native invasive species.
So while you vote for this year's Ethical Awards, Evans and Pocock would
very much like you to engage in a bit of citizen science, too. See our top
10 unwanted non-native invasive species gallery. Over the next few months we're
asking you to keep an eye out for these species and to photograph and catalogue
whenever you can, sending this vital data off to the organisations listed in
each box.
"For starters we want to see how far these species have spread
nationally," says Evans. "I think citizen science and public
engagement is really important at this stage in our understanding of
conservation. As scientists it's our responsibility to be stewards of the earth
and to manage it in a way that's sensitive and appropriate. There's a moral
imperative to manage invasive species, but obviously we can't do that in teams
of three and that's where citizen science is so powerful. Everybody's data is
important. People who fish at the weekend, for instance, are the eyes and the
ears of the riverbank. The prospect of so much new data is very exciting."
So, it's over to us.