New in town? What to do with alien species

[Neil Rigby]

Guest post: What to do with alien species, asks Urban ecologist Ian D Rotherham.

Ian with Chris Packham looking at the ecology of a Sheffield river

Impacts of invasive alien plants and animals can pose serious threats to nature conservation on scales similar in severity and significance to human-induced climate change. Once isolated faunas and floras of islands have been decimated, globalising world ecology with ecosystems erased by European colonisation.

Environmental disruption (industrialisation, intensive farming, urbanisation and climate change) mean species that are unable to adapt decline dramatically, while those able to exploit changes spread globally - the stuff of nature conservation nightmares.

Himalayan balsam, an alien, colonising species


Yet science and culture blur and blend for this interaction of people and nature. With rigorous scientific evidence, and issues seemingly clear-cut, immediate 'knee-jerk' responses are that we know which species are naturalised exotics, we know where they are, and we should eradicate.

Reality is more complex but effective debate is challenging. The media loves sound-bites and 'sexy issues' so alien invasions with clear simple messages are easy. But subtle complex debates are less newsworthy. Alien species establishing and naturalising potentially wreak havoc amongst native ecosystems, yet with few exceptions, people are unwilling or unable to do much about this.

Mediterranean fig


Most harmful invasions go unchecked; impacts run their natural course with global ecology 'Disneyfied' and local or regional character and distinction lost or diluted. This occurs in evolving and changing landscapes with both natural and human influences. Like climate change, not all effects are human-induced, but subtle mixes of natural changes and those catalysed by people. Species and ecologies are dynamic not static, changing over decades, centuries, or millennia.

Alien species are plants, animals or microorganisms not 'native' to an area but accidentally or deliberately introduced by humans. About 1 per cent becomes invasive and 0.1 per cent of aliens are damaging. Species spreading across the planet is not a new phenomenon but recent horror stories have triggered debates amongst ecologists, politicians, industry, and the public.

Some 15 per cent of Europe's 11,000 aliens have environmental or economic impacts with damage to the UK economy estimated at £2bn annually. Behind the headlines are questions of what is native and where, what is alien and when: Spanish bluebell, eagle owls, Canada geese, 'big cats', beavers, signal crayfish and wild boar - which get a free pass?

Japanese knotweed

In a once biologically dead, urban industrial river for example, colonising plants like sycamore, Himalayan balsam, Japanese knotweed, buddleia and giant hogweed, mix with native willows and alder and ground floras of native bluebells, wood anemones, woodrush and greater stitchwort. Under the shelter of the dense knotweed, play families of native otters in turn squeezing out invasive American mink.

The recombinant ecology, whether we like it or not, is here to stay in our changing world. If problems are caused, then the answer is to manage them, and that is a long-term commitment and costs money. The issue is not whether species are 'alien', but whether they cause environmental problems. Invasive native bracken and birch, for example, can destroy heathland and grassland ecologies.

Brown hare is a celebrated Biodiversity Action Plan species but exotic. The humble rabbit, a keystone ecological animal in Britain, vital to chalk grasslands and to predators like common buzzard, arrived with the Normans.

Professor Ian D Rotherham is author of 'Invasive & Introduced Plants & Animals: Human Perceptions, Attitudes, and Approaches to Management'. Watch Chris Packham discuss the alien species on Autumnwatch, 8.30pm 18 November on BBC Two.



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