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Getting a grip on urban invaders

Craig MacAdam has seen firsthand the impact of invasive species on native wildlife in his home town.
Here, he gives some tips for how to prevent 'urban invaders' escaping your own back garden.

May 2019

My walk to the train station in the morning takes me along a boundary wall with the railway. This wall has probably been there for the best part of a hundred years, and over that time it has developed in to an amazing habitat for all manner of plants and invertebrates. When I first started walking this route, the wall was adorned with many different species of native wild plants: Hawkbits (Leontodon spp.), Toadflax (Linaria vulgaris), Ragwort (Senecio jacobaea), stonecrops and mosses all had their own niche on the wall. Solitary bees were nesting in the old mortar, woodlice could be seen roaming over the stonework and tiny Chrysalis snails (Lauria cylindracea) hid under the mossy cushions on top of the wall.

However, this impromptu wildlife patch was under attack. Seeds of plants from neighbouring gardens had found their way to the wall and germinated in the tiny patches of soil between the stones. Soon there were carpets of Ivy-leaved toadflax (Cymbalaria muralis) all along the wall. Originating from middle and south-eastern Europe, Ivy-leaved toadflax is a popular garden plant which has escaped the beds and rockeries of nearby houses and made its home on the wall. Fortunately it isn’t particularly invasive, but that can’t be said for the next invader.

Buddleia (Buddleia davidii) is a brute of a plant. First introduced from China in the 1890s, it is popular with gardeners as it produces nectar rich flowers which attract butterflies and bees to the garden to feed. The problems start after it has flowered. Each Buddleia bush produces hundreds, perhaps thousands of tiny winged seeds which are picked up by the wind and blown in to the surrounding area. The seeds don’t need much soil to get a foothold which means they can establish almost anywhere. Railways are a particularly favourite spot for Buddleia. The whoosh of passing trains picks up the seeds and carries them further along the tracks. Dense stands of Buddleia can form on nearby land, crowding out native vegetation and the wildlife found in these areas.

The first sign of Buddleia on the wall was a couple of wiry sprigs. Now, five years later, the Buddleia is taking over. The seeds of these pioneer plants are colonising new parts of the wall. Huge woody trunks are breaking the wall apart, and now the fragile ecosystem of the wall is under threat.
There are nearly 2,000 non-native species established in the UK. These species have been transferred, either accidentally, or intentionally, from their native habitat elsewhere in the world and have found conditions suitable for them to survive in the UK. Many of these species are found in our towns and cities, where they have escaped from gardens or been unwittingly brought in with plants or other products. Like Ivy-leaved toadflax, not all of these species cause big problems, but some, such as Buddleia, can become invasive, crowding out other species or damaging the environment that they live in.

For gardeners, there are some really simple things you can do to prevent the spread of invasive non-native species.

  • After flowering, remove the seed heads of Buddleia and other plants to prevent their dispersal on the wind;
  • Buy locally grown plants, or grow your own to prevent new non-native species arriving in the country;
  • Report non-native species using iRecord and take part in surveys such as Potwatch.

Craig MacAdam, Conservation Director, Buglife

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The opinions expressed in this blog are the author's and not necessarily those of the wider Link membership.