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During late May 2021, the GB Non-native Species Secretariat and partners are organising ‘Invasive Species Week 2021’. Non-native species are often called invasive alien species – for simplicity we use aliens in this blog. So, this is a good time to reflect on what invasive species are and where they ‘fit’ ecologically and in terms of nature conservation. A crucial question is also how we, the most invasive species globally, cohabit with the rest of biodiversity. Clearly invasive species, typically non-native, can be very bad news indeed. Simply put, in economic terms the impacts are colossal, and furthermore, the costs are rising rapidly. Nevertheless, the situation is not so straightforward or simple as appears at first. Many assume ‘problem’ species are all invasive non-natives, yet this is often not the case

Native plants like bracken for example, come close to the top of any list of problem plants in Britain. Indeed, history and science frequently get rather muddled as to what is native. As a ‘nation of gardeners’ we love exotic flowers and, helped by urbanisation, globalisation, and climate change, many of these cultivated plants are leaping the garden fence. We do enjoy gardening with potentially invasive species, but throughout history gardeners and landscapers actively release them into the wild. This is a strong reason for having awareness-raising events like Invasive Species Week. 

However, our aspirations for achieving some control must be tempered with a touch of reality. Not only is the evidence against us making significant impacts on all but a handful of invasive species, but history is against us too. During the Ice Ages our islands have been colonised and recolonised by biodiversity for 25,000 years or more. More recently, human settlers have actively and passively introduced species for around 3,000 years. However, the pace is hotting up and our ecology is now a hybrid mix, novel and thoroughly ‘recombinant’.

Economic costs from non-native invaders are very high, although how this is calculated does affect how this is presented. Furthermore, economic impacts of non-native species must be considered from both positive and negative viewpoints. In this context, horticulture and gardening, garden tourism, economic forestry, and most of all agriculture all rely heavily on exotic species and cultivars worth billions of pounds to the UK economy. Additionally, in some areas economically significant plants such as Sitka spruce are also major invasive problems.

With invasive animals there are big questions regarding time of arrival, how it arrived, is it native, non-native or honorary native, and why is it a problem. If a species, either native or exotic, is deemed problematic, is there anything we can do to minimise or eradicate it? Following from this question is whether necessary actions are possible and acceptable or desirable, and critically, are we prepared to pay? We know, for example, that grey squirrels are non-native, destroy the eggs and young of native birds, and have economic impacts on forestry. However, would the British public, landowners, foresters, and conservation bodies really be prepared to take effective action to either control or to eradicate the species? Also, would it really be possible? The answer to both questions is probably ‘no’

The signal crayfish is an invasive alien problem species from North America deliberately introduced to Britain causing the almost certain extinction of the native crayfish. However, across swathes of the English Midlands for example, this highly damaging invasion has taken place with virtually no attempt to stop or even slow the process. There have been high profile efforts such as the eradication of coypu and muskrat in the mid-twentieth century, and then more recently to near removal of ruddy duck, but these aside, success has been limited. Furthermore, the actions proved contentious and controversial hindering complete success and leaving long-term implications. 

These examples suggest that we need to reconsider how best to live with invasive non-native species minimising adverse impacts while recognising our complex nature-cultural interactions. Invasions of both native and non-native species are mostly caused and exacerbated by human impacts on the environment – typically poor land-use choices. These include removal of native species, creation of invasion opportunities, , chronic stressing of ecosystems, and the globalising of species distributions. To address long-term problem species we must accept that our current ecosystems result from eco-fusion processes over many centuries. 

We need to decide what mix of ecology we want in the long-term and why, whether this is possible, and how can it be achieved realistically and economically. We should focus on ‘problem’ species rather than ‘aliens’. We must also accept that the decisions we make are subjective assessments of what, where, why, and when there is a problem! Science can provide objective assessments even though the ecological history is frequently wrong, but the ultimate decisions are choices people must make. Whatever we decide, history is not reversible. Our future ecology will be a fusion of long-term natives, honorary natives, and aliens. Adverse impacts can be minimised only by fundamental changes in the way that people interact with nature; the rest is tinkering around the edges.

Ian D. Rotherham and Peter Bridgewater are at the Advanced Wellness Research Centre, part of Sheffield Hallam University. Views expressed in this article are those of the authors, not necessarily those of Bright Blue.