Invasive species - are they always bad news?

| 15th June 2009
Invasive species
Native species = good; invasive species = bad, right? Not necessarily, says Dr Peter Bridgewater. Try taking a longer term view of ecology...
There are plenty of other examples where invasives are not only relatively gentle in their impact; they are also our ammunition to help manage in the face of climatic changes

22 May 2009 was International Biodiversity Day, and this year’s theme was Invasive Alien Species (IAS) - one of the greatest threats to biodiversity, and to the ecological and economic well-being of society and the planet - according to the Convention on Biological Diversity, the 'manager' of the International Day.

A recent news analysis on this website discussed the problems of aquatic plant invaders, noting from government website reports that: Invasive non-native plant and animal species are the second-greatest threat to biodiversity worldwide (after habitat destruction). They can negatively impact on native species, cause damage to the environment, the economy, our health and the way we live.

For a number of invasives I am afraid this is undoubtedly the case. Yet we need to remember that after the retreat of the ice from Britain at the end of the last ice-age, everything was an invader, jostling for its niche and reforming landscapes and ecosystems with typical ecological vigour. Alas, there were no long-term ecological observations then, but if there had been, many species, common at first would have been seen to go extinct, or at best remain with low populations.

Certainly our accidental and (alas) deliberate introduction of plant and animal species around the world has destabilised some ecosystems that have all but collapsed under the impact of invasives. But is it all doom and gloom? In fact, there are plenty of other examples where invasives are not only relatively gentle in their impact; they are also our ammunition to help manage in the face of climatic changes.

With a wide range of introduced species, including some seen as invasive, novel ecosystems are being created, and these offer hope for the fight against biodiversity loss, and also help with adaptation to climate change. So in essence we should focus on biodiversity change and how we manage it, rather than wringing our hands about biodiversity loss.

Let me give just one example from Norfolk Island in the south pacific: the Norfolk Island green parrot, Cyanoramphus cookie. It has a total population currently estimated to be less than 200, with a small number of known breeding pairs. The current recovery plan proposes establishing and maintaining sufficient predator-free nest sites for 25 breeding pairs on Norfolk Island, and establishing a second breeding population on nearby Phillip Island. Phillip Island, however, has had its glorious native vegetation devastated by goats and rabbits over the last 100 years, but both are now exterminated, although not before a moonscape was created. Natural and artificial regeneration of the natural vegetation is being undertaken, but has a long way yet to go.

At the same time, (highly) invasive plants including African olive and red guava are spreading rapidly on Phillip Island. These same plants are also a major problem on the edge of the remaining rainforest, declared and managed as Norfolk Island National Park. The National Park undertakes a programme of removal of these species (very labour intensive) and replacement by native stock locally reared on-island. 

The principal diet of adult green parrots appears to be a variety of native seeds, fruits, flowers, and leaves, but ironically with seeds, fruit and bark of African olive and red guava are also consumed! These species may now form a significant part of the diet of newly-fledged juveniles. If these plants are eliminated the parrots cannot continue their recovery. So a balance needs to be made between complete elimination of these invasive species, or phased reduction whilst the parrot population increases. On Phillip Island, the introduced plants may well help the establishment of the parrots, given the low level of native vegetation. This situation will continue for several decades into the future.

So, even really nasty invasives may have roles in helping us manage our ecosystems, which is not to argue for complacency, just a large dose of realism and less so of fundamentalism. However I am certainly not advocating a laisser faire attitude to Polygonum japonicum, the Japanese knotweed, which is as close to a triffid as you are likely to meet!

The Convention on Biological Diversity has a news item on its website about a group in India which have actually put an invasive species (Lantana) to some good use – promoting it as a substitute for bamboo and rattan to local people. These people have had access to those traditional resources denied because of conservation concerns, yet using the introduced species has helped them improve their livelihood and is also allowing native plant species restoration.  Of course, there will be a balance point where use (and maintenance) of an invasive inhibits restoration, but that point is yet to come.

There are plenty of other examples where invasives are not only relatively gentle in their impact; they are also our ammunition to help manage in the face of climatic changes

I think this shows we have to much more creative about conservation, and I suggest the following steps make up creative conservation:

•           manage for change and with change, not against it;
•           expect surprises;
•           monitor results and be prepared to change;
•           encourage and educate the wider public; and
•           embrace conservation as the heart of sustainability.  

We know the target to reduce or halt the rate of loss of biodiversity by 2010 will not be reached – we must redouble our efforts to achieve this in the next decade. Our future approach to conservation will need new ways of looking at protected areas, new ways of dealing with species conservation, all of which will challenge our existing assumptions and approaches to conservation, including how we view and treat invasive species. But leaving things alone is no longer an option.

Peter Bridgewater is Chair of the Joint Nature Conservation Committee


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