Invasive Aliens – What’s it all about?

So, contractors, how do you explain “Invasive Alien Species” to your clients?

It can all sound a bit like the X-Files when talking of ‘aliens’ taking over the land… Do you go down the route of explaining about the ease with which the plants are spread? Or go down the “Need-for-biodiversity” route? Or do you just tell them “It’s the law…”?

Most people understand about the problems with Japanese knotweed – but they tend not to understand why the plant is on their land, where it has come from and how it got there.

The easiest route to gaining an instruction from a client is sometimes to ‘scaremonger’ – by talking about Japanese knotweed growing through concrete, causing damage to hard surfaces and re-growing from the tiniest of fragments.…

… Showing blisters and burns caused by Giant hogweed tends to raise a purchase order…

… Telling horse owners about the number of animal deaths caused by liver failure brought on by consumption of ragwort, will create a worry for equestrians…

But, is the drama and fear that these plants create really the reason that they need to be managed and controlled? Far too often, I talk to clients who do understand that invasive species need to be dealt with – but who, when pushed, could not explain the reasoning behind the treatment plans they are implementing.

Other people believe that trying to stop the advance of ‘alien’ infestations is like trying to stop the tide coming in. Climate change and the global movement of goods gives massive opportunity for the spread of new species into previously unattainable locations… why should we even bother to try and manage these changes and the spread and establishment of these new invaders?

And what about those types of invading species that have wonderful flowers, provide pollen for insects and brighten up otherwise-dull riverside locations without causing any perceived ‘harm’?

Is a lack of a clear understanding from our clients down to us as contractors? And what can we say to defend our stance as contractors working to eradicate these infestations, when confronted by such simplistic and appealing arguments?

As professionals, I believe we should be taking the time to explain the reasons behind the recommendation for removal strategies and to explain the control methods used.

For example: yes, Himalayan balsam is attractive and provides a great source of pollen for bees – but – the bees are drawn to the balsam pollen because of its potency and become so addicted to the stuff that they no longer pollinate our native species. So, we have a plant that spreads rapidly and which has an explosive method of reproduction being favoured in both the pollination and reproduction battle. This doesn’t bode well for native plants and the native species that predate upon them.

Another example: while some people claim that half of the cases of livestock poisoning in Great Britain result from the ingestion of ragwort, there is firstly no way to distinguish such cases from poisoning due to aflatoxins (caused by mould growing on feed), and long-term data on cattle poisoning shows that bracken and oak were responsible for more than double the amount of cases reported for ragwort / aflatoxin poisoning. Improved stock management, a greater understanding of plant species in general (and above all, fairer gate prices to enable farmers to actually implement this) might make significantly more impact than simply spraying away any ragwort that we come across – ragwort, of course, being a native species and supporting over 40 desirable insect species, pollinators and cinnabar moth caterpillars.

These and many more examples show why I believe that each perceived problem species should be looked at with an individual perspective.

Maybe global demonisation of certain plants shows a lack of understanding of what is taking place on a larger scale. What if, on a contaminated brownfield site, we find nothing that will grow due to the poor quality of the soils, but then Japanese knotweed takes hold? Should we immediately run out and chemically treat and eradicate the plant, or should we be celebrating that something is growing where previously there was bare ground?

Perhaps this question would be answered by looking at the long term aims for the site? If it is to remain undeveloped, then having the area ‘green up’ would seem beneficial from a point of view of biodiversity, potential to improve the natural land value of the site and even carbon capture. However, if the site is to be developed as a housing estate or industrial land then maybe control and eradication of the Knotweed would be advisable.

I would like to think that INNSA’s members would be able to get into intelligent conversation about the pros and cons of alien species and could discuss options with clients rather than having a “Kill everything” policy.

Our credibility as land managers is at stake here and we must be seen to be protectors of the environment. Mass murderers and those that have carried out ethnic cleansing never do well in the history books.

Years ago, I remember a tree surgeon that recommended all sycamores be ‘heavily pruned’. By this he meant felled. Some people (including the tree surgeon in question) considered sycamore an alien species that should not grace our shores. However, if one now takes on board the potential loss of ash trees in the UK due to ash die back, the damage to oak trees by the processionary moth and the other diseases that blight our native trees, then had all the sycamores been clear-felled thirty odd years ago as he desired, we would be looking at having very few trees left in the UK.

Mike Clough
Chairman