These are becoming increasingly controversial in many countries Introductions of animals and plants, intentional or otherwise, have wreaked havoc in native ecosystems all over the world. One of our colleagues in New Zealand has spent many hours trying to rid offshore islands of cats and rats to protect ground-nesting birds. The stories of the cane toad, the giant African snail and Caulerpa taxifolia seaweed are well known, but there are hundreds of others.

In Britain, an audit of non-native species in England published by English Nature (now Natural England), revealed for the first time the number of non-native species in England and the impacts they have on the environment.

Two thousand, seven hundred and twenty-one non-native species and hybrids have been found in the wild in England, including 1,798 flowering plants (making up 73% of the total) most of which have escaped from gardens. Detailed analysis was carried out of 1,413 species considered to be most significant and showed that 1,177 are considered to be established in England.

Most non-native species don’t cause any environmental or economic problems but some can cause considerable damage. Japanese knotweed, for example, can grow through concrete, damage property and destroy habitats by swamping the other plants.

Invasive alien species impact on biodiversity and the natural environment by displacing or preying upon native species, by changing habitats, or by introducing new diseases or parasites. The invasions can have serious economic and ecological consequences. The ecological cost may be the irretrievable loss of native species and ecosystems, including loss of characteristic local distinctiveness. The English Nature report identifies nineteen species which have strongly negative environmental impacts. These include:

• Signal crayfish which carry a disease that kills native crayfish;
  
• Grey squirrels which out-compete native red squirrels and carry a disease that kills them;
  
• Chinese mitten crabs – a voracious predator which threatens native species, and in large numbers can cause erosion of soft banks;
• Giant hogweed which has a toxic chemical sap that causes skin blisters in people and out-competes other native plants and grasses.

Some alien animals and plants have beneficial effects. The report identified four animals (common pheasant, greylag goose, red-legged partridge and Rhizophagus grandis a predatory beetle used for pest biocontrol in forestry) and fifty-one plants – mainly tree crops and field crops - that had strongly positive economic impacts. Others have mixed effects, for example, Buddleja (butterfly bush) is considered beneficial as a useful nectar source for some insects, notably butterflies, but can also colonise bare ground habitats important for other invertebrates, such as the bombardier beetle. It also has a major negative economic effect, because of the cost of herbicide applications along railway lines to control it.

In the last twenty years, some invasive non-native species have increased considerably, at least doubling their numbers, including the freshwater fish topmouth gudgeon, Canada goose, Chinese muntjac, New Zealand pygmyweed and butterfly bush. New species continue to arrive and spread rapidly, for example the horse chestnut leaf miner, which probably first appeared in 2002.

Introduced animals occupy a wide variety of habitats, but plants are more selective, being strongly concentrated on cultivated, built and derelict land. This has potentially important economic and environmental considerations for towns and cities where many of these new species are establishing and can be very expensive to remove.

Invasive species also affect sustainable development and land or resource management, and can result in impacts on human interest, for example by causing financial losses or public health issues. Natural England confirm they will now use these results to decide which alien species pose a threat to English wildlife and how they can be tackled. Other countries are pursuing similar policies.

Betts Estates inevitably come across invasive alien species on their UK sites and have to control them. Japanese knotweed (our protocol JK) is perhaps the commonest and an information sheet is available for download here. We can assist with the ecological science and options for control of all invasive and pest species.

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