Invasive species

What is ‘an invasive species’? We use the term frequently but often flexibly. This post aims to clarify this.

Definitions of the term ‘invasive species’ use a variety of wording, yet all share the same three characteristics. These are:

  • The species is non-native and has been introduced to Britain either by design or by accident.
  • It has the ability to spread or has already done so.
  • It has the ability to cause damage to our ecosystems, habitats or native species (and perhaps our economy and well-being) or has already done so.

In a nutshell, the invader, therefore, has arrived, thrives and does damage. This applies to animals, plants, fish, insects . . . you name it (although this post considers only plants). Just one or two of these characteristics is insufficient for a plant to be called invasive. It needs to demonstrate all three: “arrived, thrives and does damage”.

The UK government’s own website is where Schedule 9 of the Wildlife and Countryside Act of 1981 has its home. This lists the plant species that are deemed to be invasive species. There are nearly 55 plants listed there. (The Royal Horticultural Society, which uses the same definition of invasive plants, lists 78 such species.) Only four of the cemetery’s 210+ flowering plant species are on these lists:

Official guidance on invasive species in England is that:

You must not plant in the wild, or cause to grow in the wild, invasive non-native plants. This can include moving contaminated soil or plant cuttings.

If you find invasive non-native plants on your land, you must stop them from spreading and causing a nuisance or damage to other land or property. If you do not, you could be responsible for any damage they cause and may be prosecuted.

Natural cycles of feast and famine

There are other flowering plants that appear to be invasive. These are ones that can, in certain years, flourish and expand from one grave to another. They give the impression that they are invading an adjacent area within the cemetery, as well they might be, but they will be doing so in a natural cycle of growth that one year can cause them to flourish, and another year can cause them to almost vanish. This is entirely natural for many of our native plants. Examples of this are Common Ragwort from several years ago, and this year Hogweed (not the invasive Giant Hogweed, which isn’t found in the cemetery). When these annual expansions happen, they do so without the risk to our environment (or economy or well-being). If a plant isn’t one of the 55 or so plants listed on Schedule 9 of the Wildlife and Countryside Act of 1981, then it isn’t an invasive species.

These boom years for native plants are just as likely to be followed by a famine year and, in this sense, nature manages itself well enough without our need to intervene.

Non-invasive native plants that nevertheless need managing

We have a very small group of native plants that are neither booming nor doing damage, but are ones that are always on the march, typified by Ivy and Bramble. We do not wish to sit back and see them march ever onwards, so they become subject to careful and judicious management. We leave enough for dependent insect, butterfly and bird species to benefit from them, without allowing them to take over, but they aren’t invasive. Invasive plants are the ones that “have arrived, thrive and do damage” and because of that are listed in Schedule 9 of the Wildlife and Countryside Act of 1981.