Problem? What problem….?

Author: Mike Clough

Date Posted: Wednesday 17th February 2016

When the scientists talk about Alien species doing ‘harm’ – what is it they are actually talking about? The 8th Convention on Biological Diversity asked for … action to…’prevent the introduction of those alien species which threaten ecosystems, habitats or species’.

What this implies is that for consideration a species must be new to the region (alien) and must threaten the native flora and fauna.

This is defined as causing ‘actual ecological harm’.

When I’m talking to people about Japanese Knotweed they often ask – why is it so problematic – then follow this up with … ‘Surely its spread is just part of global warming’ …or they think its just part of … ‘progress’…or… ‘evolution’…

One of the phrases that I hear repeated is that these alien species were all… ‘accidentally’ .. introduced however the truth is that many were deliberately planted. In America for example 85% of the woody species were introduced for horticultural purposes. Many of the grass species introduced to Australia for pasture became problematic whilst only 5% turned out to be useful.

The spread of Japanese Knotweed is partly due to its ability to grow from the smallest of fragments but it’s also to do with a more complex story. If every species that arrived on our shores behaved as Japanese Knotweed did… then we would be totally over-run.

So we must ask – why do certain plants become invasive and others don’t?

Only a fraction of the alien plants that land on our shores actually become established – and an even smaller fraction become a serious problem. There are a variety of reasons for this disparity in growth habit – alien species have evolved ‘somewhere else’ and have left behind all of the co-evolved species when they were moved to the British Isles. They have also left behind diseases and predators which would have kept their progress in check – so often they have a growth advantage over our native plants. Some species can cope with our climate whilst – others may struggle with higher or lower rainfall levels or temperature extremes.

There are also great debates about whether particular plant is causing a problem. It took many years for the issues with Japanese Knotweed to be recognised.

Generally, an invasive species that is expanding its range in new region and having negative impact is easily identified –

Impacts can include:

Species elimination

Water depletion

Crop damage

Forest damage

Fishery disruption

Navigation impediment

Clogging water works

Destruction of homes/gardens

Loss of grazing land

Given the impacts of alien species we have great motivation to alleviate the problem – however there are some basic problems in doing so – not least of which is that invasive species are self-replicating.

If one had to clean up an oil spill or example – complex though this is – once it’s cleaned up the work is done. With invasive species unless one manages the situation properly …the infestation will simply grow back. Invasive species can also adapt and evolve mechanisms to overcome control efforts. Once an invasive species integrates itself into an ecosystem its control becomes far more complex due to its interaction with other species.

‘Horizon planning’ is a new buzz word in the industry – meaning that we should be looking ahead and identifying future problems. It is a recognised fact that eliminating a species before it gets a foothold is far more cost effective that trying to eliminate an established plant…. The problem with this is being able to recognise when a plant becomes truly invasive. This is complicated further by ‘lag times’ – this being the length of time between when a plant becomes established and when it becomes invasive. Lag times can be many decades – or even centuries …making observation and reaction almost impossible.

One must also remember that there is some good news about alien species in that they serve as the foundation for our food production systems. If you think about our food supply – only about 20 plant species contribute to major food source …and pretty much all of these are grown far from their places of origin. These species have been moulded through selection and engineered to fit local conditions in the most productive manner possible.

Alien species have also been used by our Landscape Architects and garden designers over the years to ornamental purpose in our gardens, parks and stately homes.

So it’s not all bad news…


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Mike Clough

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