Alien Invasion in Stinchcombe

It’s happening right now – not people but non-native invasive plants. Human visitors are, of course, very welcome to our village.

What did the Victorians do for us?

Lots of things, however, introducing Japanese knotweed and Himalayan balsam was not their finest contribution. No doubt at the time they seemed like fascinating additions to the garden, real talking points. We can’t blame them for another non-native invasive species, Cotoneaster, which arrived over a decade before young Victoria came to the throne.

Legislation

I have singled out these three because they are causing problems locally. There are many others covered by the legislation on invasive non-native plants. The Royal Horticultural Society gives an excellent introduction from a gardener’s perspective.

In brief, the RHS say:
• the listed species are banned from sale (this doesn’t appear to be the case with the listed species of Cotoneaster!);
• they should not be planted or caused to grow in the wild; and
• we should take measures to control any already present in our garden.

Let’s have a closer look at our three invaders.

Japanese knotweed

Japanese knotweed was imported from eastern Asia in 1886 as an ornamental garden plant. It can grow quickly and vigorously just about anywhere, even breaking through concrete and tarmac. This has obvious threats for buildings and infrastructure.

How it spreads

The plant spreads by the growth of rhizomes, which are underground stems that send out roots. Even a tiny piece of rhizome inadvertently moved with soil or equipment can generate a new plant. Look how the knotweed, with its copious small creamy flowers, has taken over on the public land in the photo! This site is in North America but the same can happen in the UK.

Legal position

Whilst it isn’t illegal to have Japanese knotweed on your land, you can be prosecuted if it spreads into the wild. A civil case could be brought against you if it colonises neighbouring properties. It is not a notifiable weed; however, you must declare its presence if selling your property. A least five pieces of legislation are relevant.

A growth industry

Unsurprisingly, a whole industry has sprung up around Japanese knotweed control. The control methods available are:

• repeated spraying with professional grade glyphosate-based herbicides for at least 3 years
• physical removal and disposal as a controlled waste under the Environmental Protection Act 1990

A combination of these methods is often used. Most people are likely to need specialist help to ensure that control is successful and stays within the law.

Where is it locally?

Japanese knotweed is present in at least one place in Stinchcombe. At the request of a resident, I recently reported a patch on the verge alongside Standle Lane, using the Gloucestershire Highways online reporting system.

It looks innocuous in the photo, but without appropriate action that could soon change. Highways have added the area to their contractor’s list and the Parish Council will be monitoring progress.

Himalyan balsam

This rather attractive plant was introduced to the UK in 1839, from the Himalayas as the name suggests. It thrives on riverbanks and in damp woodlands.

What is the problem?

Why worry when the prolific pink flowers are so pretty and the bees love them? The problem is that Himalayan balsam grows fast, reaching a height of up to 3 metres. Exploding seed pods can project as many as 800 seeds per plant up to 7 metres, enabling it to spread rapidly. It quickly crowds out our native woodland species, reducing biodiversity. A further problem is that when large areas of balsam monoculture die back in the winter, the bare soil becomes vulnerable to erosion.

Where is it locally?

On the Dursley side of Stinchcombe Hill, Himalayan balsam has become well-established only a few years after it was first spotted. The Cam, Dursley and Uley Joint Woodland Management Committee is running conservationist work parties (see photo) to pull out as much as possible before it sets seed. Unlike Japanese knotweed, the pulled plants can be broken, trampled and left on site.

Cotoneaster

It was a surprise to see five species of Cotoneaster on the list of invasive alien species. They are widely available to purchase, often with no warning about their status. (There are also many other Cotoneaster species that aren’t on the list.) The first plants arrived in the UK from East Asia as long ago as 1824. They are useful ground cover and provides berries for the birds. Unfortunately, the birds spread the seeds to sensitive habitats. Limestone scree, such as on parts of Stinchcombe Hill, is especially vulnerable. Cotoneaster can eventually crowd out native flora and develop extensive root systems. Ecologist Elizabeth Kimber has written an informative article.

We’re part of the problem

Our own back garden contained two types of Cotoneaster when we moved in 26 years ago. As far as I can tell they are horizontalis and microphyllus, both on the list. They have certainly been spreading, in spite of half-hearted attempts to control them (see area in front of the bird bath).

Impact on Stinchcombe Hill

As a conservation volunteer for over a decade, I have observed an increase in the amount of Cotoneaster appearing on the upper slopes of Stinchcombe Hill. We try to root out any plants we see, but it is a huge area to monitor. Even the small plants can have long roots that it is difficult to remove completely. My garden, and possibly yours, is contributing to this problem so I need to get serious about tackling it.

Legal Position

As with Japanese knotweed, listed species of Cotoneaster are controlled waste. Strictly speaking, pruning’s and uprooted plants should not be disposed of to SDC’s garden waste scheme or taken to any of its household recycling centres. In our garden I am going to physically remove as much as possible, before the berries ripen, and burn it (considerately) on site. Chemical treatment is an option I will avoid unless it proves absolutely necessary.

How you can help

If you spot any of these three invaders on public land or in the wild around Stinchcombe, please let the Parish Council know. You can report infestations on roadside verges directly to Highways, as already stated in the Japanese knotweed section. It would still be useful if you informed the Parish Council so that we can follow up.

Kath Hudson