Non-native Invasive weeds – the not so good, the really bad and the ugly ones too!

I hope you will forgive the spaghetti western reference in the title (cue the haunting tones of Ennio Morricone’s theme music)? But, to kick-off Invasive Species Week 2022 (NNSS Event), I use it here to highlight the fact that there are many non-native invasive plant species but not all are dealt with in the same way when it comes to our legislature – why is that?.

Invasive weed control is an important sector. Worldwide, invasive species are thought to cause over 1,300 trillion dollars of damage annually – that’s’ how important! So it’s vital to understand why some plants are prioritised for management/control/eradication.

I’m happy to tell you there is some science (quite a lot actually) involved in the decision-making process and the Non-Native Species Secretariat have commissioned an extensive review of their 2015 Strategy document. The report includes a raft of recommendations regarding future regulation and management of non-native species and we will try to highlight some key points here.

As regards individual non-native invasive weed species, which one does Clint Eastwood ride off with in the end? Read on……

The (not so) ‘good’ invasive species

Here, by ‘good’ we mean they are known and acknowledged as problematic, and as such, they are listed (scheduled) in relevant statutes such as the Wildlife & Countryside Act 1982*. This is important because it means their presence (e.g. Japanese Rose, Himalayan balsam, Giant Rhubarb + 70 more!) imposes an obligation on landowners to control them (at the very least to prevent their spread) and that wastes arising (which contains propagules, seeds or any storage organs able to re-generate) are classified as Controlled waste.

The statutes in this case have the benign effect of creating a legal incentive for action (and restrictions on sale) as distinct from any commercial imperative such as preventing physical damage to buildings etc. That is, the environmental impact of these species is deemed to be significantly relative to their peers….

‘Good’ species therefore include plants such as Japanese knotweed, Giant hogweed and Rhododendron, but why these and not others? To some extent this is a reflection of what the non-native species secretariat considered important at the time but the ongoing review (see above) may result in a broader understanding of non-native invasive species which keeps up with the changing threats to the environment.

* For a full update on all statutes regarding wildlife protection please watch this excellent webinar by Dr Julie Riley at Wildscapes Ltd.

The ‘bad’ invasive species

So the NNSS recognise, there are plenty of invasive non-natives which are problematic, but not currently under legal statutes. Lets consider one in particular – well a group actually.  By simply responding to market needs the PCA has identified a clear and present danger from a number of bamboo species that seem to love our climate and gardens – check out our webinar on Buddleia and Bamboo and details of Surveyor Training!

PCA members are well equipped to respond to the challenge of dealing with these rhizomatous perennials in urban spaces. The cost is usually justified on the basis of solving encroachment issues or preventing damage to hard surfaces or buildings. But in the wild, bamboos can spread and behave in classic invasive style, displacing native plant communities, resisting disease and providing virtually no benefits to resident insect or other animal communities.

In certain cases the Environment Agency/Defra (or environment agency bodies in Wales/Scotland/NI) can impose Species Control Orders, but these seem to be used rarely, and never for bamboo species to our knowledge. That’s why we’re calling these species (under the radar so-to-speak) the ‘bad’ guys – because they do as much damage as other non-native invasives but are getting away with it (not listed)!

…and the Ugly prize goes to…?

Now let’s think about the real underdogs and give an example – Poison hemlock! This plant is a classic example of non-native species that has been around for so long it seems to be part of our native flora – semi naturalised. In this case Hemlock wins the ‘Ugly’ prize because of its poisonous properties. Not that unusual for a member of the carrot family, but it is by far the most common and widespread poisonous member of the group.

By poisonous we mean it can cause some irritation/blisters or sensitisation through skin contact, but in the main the toxic alkaloids that we fear are mostly only accessible if ingested (as the ancient Greek Socrates, knew only too well). Farm livestock can be harmed, but unless someone inadvertently used hemlock as a salad leaf, we generally aren’t ‘at risk’ day-to-day.

So, this particular ‘ugly’ invasive is widespread, increasingly annually and can be problematic, but is unlikely to ever be considered worthy of special status in law. Perhaps the best way forward would be to include them as ‘Harmful Weeds’ (Weeds Act 1959) in an agricultural context. Unfortunately, updating this statute wasn’t considered within the scope of Strategy Review 5.

On a practical level, our advice is to assess these semi-naturalised invasives in the context of the sites where they are found; we have to be pragmatic and accept that if it is widespread and common, putting it on a Schedule of invasive plants would achieve very little of value on a national scale.

So how does it end for the hero in this story?

Perhaps the analogy I’ve tried to run with here is slightly inappropriate – we’ve labelled the really important (Schedule 9 etc.) weeds as ‘good’ on the basis that the legal status afforded to them helps us achieve benign outcomes for the environment. But the moral of the story is that we can have lots of exotic (non-native) plants to cherish/admire in gardens etc. but we need to be ‘savvy’ about which ones might run amok given a chance and this includes lots that are not listed and may even be considered semi-naturalised!

Is there hope of a ‘happy ending’?….cut to scenes of Clint riding into the sunset clutching not a pot of gold, but a potted plant which we can see is a Phyllostachys bamboo – he’s an invasive weed ‘hero’, but he also knows that the only way to keep a ‘running’ bamboo species, is to buy it in a pot and keep it in a pot!

Invasive Species Week Info Hub

A reminder that its Invasive Species Week 16th – 20th May and we hope you will engage with as many online or in-person events as possible – and look out for further resources being shared by the PCA via our Invasive Species Week Info Hub. Remember that when it comes to any and all invasive weed management issues the PCA’s Invasive Weed Control Group members can offer professional advice and guidance.

To summarise, ALL non-native invasive species are inherently ‘bad’, even the ‘good’ ones and particularly the ‘ugly’ (poisonous) ones…

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