Tuesday, 24 January 2012

Invasive species, friend or foe

A couple of weeks ago, I had a walk around the National Trust’s Wicken Fen in Cambridgeshire. Quite a blustery day, so windy in fact I seemed to be the only visitor on the reserve. The assistant in the visitor centre showed mild surprise I wished to venture out into the reserve on such a storm lashed day, with the comment “how hardy are you?” Well I am hardy, but after an hour of being buffeted and battered as the winds hurled themselves from the North Sea and across the flatlands of this area, I decided to hurl myself into a sheltering hide for a respite.

Sitting in the hide, windblown but unscathed, in front of me were a myriad of finches and tits desperately clinging onto the oscillating feeders, and 3 grey squirrels. It was while watching the antics of these alien mammals to the British countryside that the embryonic stirrings of this blog developed. In the sunlight and the wind, these North American invaders looked stunning and completely at home here on the Fens as they grappled with the peanut feeders. It’s hard to imagine therefore the devastating effect they’ve had on out native red squirrel, as the vector of the squirrel pox virus.

But look around the British countryside and I can guarantee you won’t need to look far before finding an invasive species, anything from the “iconic British” snowdrop, to Munjac deer, harlequin ladybirds, Canada goose or even the exceptionally widespread bête noire sycamore Acer pseudoplatanus which was introduced sometime between the Roman era and the 17th century.

So what exactly what is an alien species? Biologists have identified over 11,000 alien species in Europe, but while the majority of these are not troublesome, approximately 15% are known to have some impact on the environment. Much has been written about this, but while watching the grey squirrels, I thought more on the question, how alien is alien?

Invasive species are often labelled as the greatest threat to the world’s native wildlife, derided and eradicated with a zeal and vigour. Undoubtedly some species are very detrimental to the British countryside, either outcompeting native species, or vectors of disease, but the vast majority fill a niche which happily coexists with native fauna and flora. As I’ve mentioned, come January we all look at snowdrops and think, ahh spring is on its way. But we forget that snowdrops are not native to the British Isles, and were probably introduced in the 16th Century, or maybe as far back as in Roman times.

A few years ago an attempt to tackle the issue led to the formation of a European Commission funded DAISIE project (Delivering Alien Invasive Species In Europe) and headed up via the Centre of Hydrology and Ecology in Wallingford. Its aim was to attempt to log invasive species across Europe in order to understand the problem.


Terminology is also confusing, exotics, invasive, invading, alien, but what exactly are we talking about here? It is difficult to exactly define this, but put simply, an alien species is a species brought to an area through man’s activities. In other words it hasn’t got here by normal habitat or range expansion. That seems simple enough.

But this can then be subcategorized into non problematic species, those which can exist in the wild but do little harm, so we could include the snowdrop. And problematic species, those which cause impact to ecology of the environment or have an economic impact. These are probably better known as invasive species, and the ones which often grab the attention of the press. The cute looking muntjac deer would fit this category, now widespread after being released from Woburn they have a huge impact on woodland native flora as they browse herbage in flower, thus reducing vigor, affecting nesting sites and can destroy gardens. We could also have a category of non-problematic climate change species. Currently these have no or little impact on native wildlife, but with climate change may do so, for example southern hemisphere plants which may become established in warmer climate.

A possible example of this is affecting the Breamore Marsh in Hampshire’s New Forest. In August 2009, botanist Clive Chatters discovered a small patch of Creeping Water Primrose, which comes from Central and South America. Since then 14 sites have been found in south east England. Although released by accident into the wild, it is thought as the climate in Europe warms, this plant is able to colonize areas once deemed too cold to become established. In France this plant is now a huge conservation problem.

Legislation for alien species came about with the arrival of Schedule 9 to the Wildlife and Countryside Act 1981 http://jncc.defra.gov.uk/page-1377 which makes it an offence to deliberately release or plant or otherwise allow to grow a non-native species in the wild. But across Europe there are over 50 different pieces of legislation. It is complicated so in 2008, a cross British strategy was set up, the Non Native Species Secretariat. http://www.nonnativespecies.org/. From this site I was surprised to learn that in England there are 2,721 non-native species, of which 66% are plants and in Scotland in 2000, 988 species of which 70% were plants.

The Royal Horticultural Society have long campaigned for responsible imports of horticultural flora, especially if pot grown, as vectors of fungal disease and pests. Indeed the recent arrival of the fungus Phytophthora ramorum is rapidly wiping out larch species in Britain. This phenomenon wasn’t well documented until 2009 until it was discovered in the south west of England. Indeed I was shown some of the first affected areas back then. It is thought it has arrived from horticultural stock, however the non-native and often highly invasive rhododendron is also a target. Could this fungus have a benefit in the long term in helping control rhododendron? In most British gardens about 70% of plants are non-native and the vast majority non-invasive. But care at disposal is needed.

So is there a dilemma maybe?

When is an alien species a problem, and when is it just a happenchance arrival on our shores with little effect on the native wildlife? In a recent article by Dr Thomas Ings is at the School of Biological & Chemical Sciences at Queen Mary University, London he discussed the use of the bumblebee, Bombus terrestris as a commercial pollinator. As a result the species has become established in 2 countries, Chile and Japan. Commercial growers also use the subspecies, B. terrestris sassaricus, which can hybridise with the native B terrestris. However in areas of France where the subspecies had escaped, although fears of hybridization would wipe out the native bumblebee, it seems the, the latter had out competed it for food and resources and in a study, 6 years after being found living wild, no sightings of B. terrestris sassaricus were made.

But are we conditioned to think of some species, especially the nice to look at species, as a native British species? A quick look on the internet will throw up some surprising facts. Christopher Lever, a naturalist who has studied naturalized animals in Britain for 50 years. He says the first species to be introduced to Britain was probably the house mouse that came over with Neolithic man. Hard to think the house mouse being non-native as it chomps its way through your cheese store (actually they prefer sugary items, not cheese). 

Other experts claim that the threats posed by invasive species have been exaggerated and that many native species can be equally destructive. Professor Christopher Smout, from St Andrews University, is one who recently argued this "culturally-determined" idea of native and non-native species is fundamentally flawed.

Reading the Naturalized Animals of Britain and Ireland, the general assumption is that generally it is a very bad thing to introduce an alien species outside their natural range because in most cases they damage the surrounding environment. However with current projects to reintroduce once native species into the wild such as sea eagles, beavers and red kites, are we any more at risk of creating a wildlife crisis as the control measures for these species are now often none existent?

So am I any clearer in this topic? Well yes and no. Some introduced species are obvious candidates for eradication, such as the Japanese knotweed, but if someone suggested eradicating snowdrops from the British countryside this spring, the word would spread like a carpet of Spanish bluebells in May. And the sycamore tree once seen as having little conservation merit is now known to become with age a microcosm for rare lichens and epiphytes in western Britain, as a result of its base rich bark. So the next time you’re observing wildlife at Watership Down, bare a thought for that iconic invasive species which inspired Beatrix Potter too, the rabbit, first brought to Britain by the Romans but only becoming established in the wild during the mid to late 12th Century.

Personally I adore the brown hare, certainly they’re non-native as like the rabbit they were brought over by Romans, although possibly they may have been native before the last ice age. Are they friend, foe or probably something in the middle happily ignoring the problem and just living free and adding to the biodiversity of Britain’s countryside?


  1. I'm glad you survived a rare ole fen blow!

    A really interesting topic.


  2. It is squirrel season here. I would suggest you get after those gray squirrels. They are monsterous even here. They have descimated the Fox Squirrel which is in my mind a better squirrel. Invasives are a sad thing sometimes. As you say though I would be sad come spring if I didn't have snowdrops. Here we could send your area a truck load of European Starling. I hear they are in trouble in your area. Here they are a pest taking the nest holes of many woodpeckers that are already in trouble because there are so few rotten trees for them to nest in. We could also send House Sparrows. We have 100+ at our feeders. Makes a person want to stop feeding them. They also take the nest holes that Titmouse and Chickadees and other smaller birds wish to use. A sad situation. The Canada Goose is supposed to be here but many no longer migrate making them a nuisance. Not to mention the Wild Mustard,Purple Loosestrife etc etc. What a mess we humans can make of a place.

  3. personally I like Grey Squirrels. For many its there first introduction to wildlife. yes its sad about the red but is it REALLY worth all that money to eradicate them.

  4. Super post Andrew - I thought I knew quite a lot about alien species but I've learnt a great deal from reading this feature.

    Emotive subject really as my heart is so against culling but when I see the havoc mink have wreaked with water voles then my head rules!

  5. A very interesting subject here but as we have virtually now squirrels at all in our corner Brittany - certainly never seen a grey one - the odd red one which are fab; I'd love to see more over here. Must admit I couldn't help being distracted by the gorgeous header photo of the piggies :-)

  6. Thank you all for the comments, from what you've said it looks like it really is an issue, which isn't easy to get to the bottom of. Needs further investigation I think, maybe a radio programme..... huuuumm that's an idea :-)