All’s fair in the invasion war

Invasive alien species (IAS) have been the focus of many a debate recently (http://www.bbc.co.uk/news/science-environment-21509016), with research in this area flourishing. Indeed for job creation purposes (make space for me in approximately 2.5 years!) the attention invasive alien plant species (IAPs) in particular are now receiving, is very welcome. However, shifting attention sparks off debates, one in particular being our  knee-jerk and almost xenophobic reaction towards anything alien within ‘natural’ ecosystems (which, let’s face it have not been very natural for hundreds if not thousands of years).

 © 2009 UK Weed Control Ltd

© 2009 UK Weed Control Ltd

IAS are widely stated to pose the second largest threat to biodiversity after habitat destruction, through out-competing native species, affecting agriculture and forestry, as well as posing human health risks (Richardson and van Wilgen, 2004). Although the threat of biological invasions is well established within the scientific literature, there is still a sizable gap in our knowledge on the true extent of impact by some well-known invasive species. This is of significant concern given the resources invested in control of IAS (Approximately £1.7 billion) given the limited resources currently made available for conservation of biodiversity. In some cases, the negative effects of IAS on ecosystems are merely assumed and often disputed. In the case of IAPs it seems there is little agreement over how much is too much and therefore how much is damaging to ecosystems. (see e.g. Hulme & Bremner, 2006 and Hedja & Pyšek, 2006). More research is needed.

Nothing lives under this Japanese knotweed patch along the Black Cart Water, other than (temporarily) myself and field assistant, David and perhaps some ground elder around the periphery of the patch.

Nothing lives under this Japanese knotweed patch along the Black Cart Water, other than (temporarily) myself and field assistant, David and perhaps some ground elder around the periphery of the patch.

From my own experience locating field sites for my research three Invasive Plant Titans dominate alongside rivers in semi-urban areas: Giant Hogweed (Heracleum mantegazzianum), Japanese knotweed (Fallopia japonica) and Himalayan balsam (Impatiens glandulifera). Indeed, one might well ask if a swathe of rather attractive, orchid-like flowers, (aka Himalayan balsam), isn’t preferable aesthetically to dense brambles and stinging nettles (neither of which is much fun to walk through…) in the built up White Cart Water in Renfrewshire?

Himalayan balsam invaded public walkway along the otherwise nettle and bramble infested White Cart Water in Renfrewshire.

Himalayan balsam invaded public walkway along the otherwise nettle and bramble infested White Cart Water in Renfrewshire.

So should we be more accepting of these ‘displaced weeds’? After all, a weed is just a plant in the wrong place at the right time, exploiting its new found environmental wealth. The same could be said for humans. A recent editorial in Nature by Chris Thomas (Thomas, 2013) has left me both intrigued and slightly frustrated. He raises the possibility that, at a time when species are declining at one of the fastest rates in the history of our planet, IAS will actually increase biodiversity through their potential to hybridise and potentially naturalise. This in turn raises the question of whether there is merit in conserving IAS?

© 2012 Garden Route Initiative, Working for Water Programme.

© 2012 Garden Route Initiative, Working for Water Programme.

Globally IAS are a recognisable issue and in some countries the consequences of a tolerable approach to invasion would be truly detrimental to the well-being of local people. For example, in countries like South Africa, IAPs pose a direct threat to water security. In this respect the public have been made aware of IAPs and their threats and programmes, such as ‘Working for Water’, have engaged with communities for almost two decades in the fight against invaders. Thomas (2013) discusses our intolerance to IAS and emphasises that money should be targeted at the battles we can actually win – a point it is hard to argue with. However, climate change and human-mediated global dispersal are together moving the goal posts and changing the combatants in invasion wars and we just cannot predict the winners and losers.

References

Hejda, M. and Pyšek, P. (2006) What is the impact of Impatiens glandulifera on species diversity of invaded riparian vegetation? Biological Conservation, 132, 143-152.

Hulme, P.E. and Bremner, E.T. (2006) Assessing the impact of Impatiens glandulifera on riparian habitats: partitioning diversity components following species removal. Journal of Applied Ecology, 43, 43-50.

Richardson, D.M. and van Wilgen, B.W. (2004) Invasive alien plants in South Africa: how well do we understand the ecological impacts? South African Journal of Science, 100, 45-52.

Thomas, C.D. (2013) The Anthropocene could raise biological diversity. Nature, 502, 7.

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