‘Super-invader’ plants like Japanese knotweed are causing flowers across the UK to lose their uniqueness and become increasingly similar, study warns

  • Researchers studied more than 650 regional floras from around the world
  • This allowed them to look at the diversity of plant species within each region
  • They compared other effects such as differences in climate and governance
  • They found that in most cases invasive species naturalise and dilute diversity 

British flowers are becoming less unique and increasingly similar, according to a new study that suggests this is due to ‘super-invader plants’ like Japanese knotweed.

Alien plants spreading into an existing ecosystem can sometimes contribute to the uniqueness of regional flora, but more often they ‘homogenise’ the diversity of plants and flowers, according to a team from the University of Konstanz in Germany.

In a new study, published in the journal Nature Communications, researchers compared the composition of 658 regional floras from around the world. 

‘Unless more effective protective measures are taken to counter the ongoing spread and naturalisation of alien plants in the future, they will continue to destroy the uniqueness of our ecosystems,’ warned study author Dr Mark van Kleunen. 

British flowers are becoming less unique and increasingly similar, according to a new study, that suggests this is due to ‘super-invader plants’ like Japanese knotweed

What is an invasive species? 

An invasive species is one – be it animal, plant, microbe, etc – that has been introduced to a region it is not native to.

Typically, human activity is to blame for their transport, be it accidental or intentional.

Sometimes species hitch a ride around the world with cargo shipments and other means of travel.

And, others escape or are released into the wild after being held as pets. A prime example of this is the Burmese python in the Florida Everglades.

Plants such as Japanese knotweed have seen a similar fate; first propagated for the beauty in Europe and the US, their rapid spread has quickly turned them into a threat to native plant species.

Climate change is also helping to drive non-local species into new areas, as plants begin to thrive in regions they previously may not have, and insects such as the mountain pine beetle take advantage of drought-weakened plants, according to the National Wildlife Federation.

To understand the true impact invasive plants have on the diversity of an ecosystem, the German team turned to a number of global plant databases comparing the composition of 658 regional floras.

They considered the number of plant species a region shares or does not share with other regions, and the degree to which plant species are related to each other.

This allowed them to assess the floristic uniqueness of individual regions.

The researchers discovered that various biogeographic factors play an important role in the spread of alien plants and the loss of uniqueness of regional floras.

This includes the geographic distance between the regions they studied, as well as their ‘climatic distance’  – how different the regional climates are from each other.

‘The more similar two regions are in terms of climate, the more likely it is a plant from one region will succeed in establishing itself as a naturalised species in the other, once geographic barriers have been crossed,’ said lead author Dr Qiang Yang.

‘In a sense, plants from a region with short climatic distance to their new habitat are climatically pre-adapted,’ said Dr Yang.

However, anthropogenic factors also have an impact on the spread of alien plants, the team discovered – that is factors caused by humans. 

For instance, the researchers said some of the areas they studied had a shared history, with the same government running them. 

‘Regions that are now or had been under the same political administration in the past exhibit greater homogenization in the composition of their floras,’ they wrote.

Areas within the US or Europe were given as an example of this shared governance. 

Historical examples, on the other hand, are the European colonial powers and their former colonies in South America and elsewhere.

‘Between regions of the same national territory or regions with historical colonial ties, there is or at least was lively exchange in the past – in the form of both cargo and passenger traffic,’ said Qiang Yang.

‘This usually also increases the exchange of plants across geographical borders, be it intentionally, as trade goods or agricultural crops, or unintentionally.’

Alien plants spreading into an existing ecosystem can sometimes contribute to the uniqueness of regional flora, but more often they ‘homogenise’ the diversity of plants and flowers, according to a team from the University of Konstanz in Germany

Overall, naturalized alien plant species are the main driving force behind a global decline in diversity, within any single region. 

‘These effects are now evident even in the most remote corners of the world’, reports Dr Mark van Kleunen, Professor of Ecology and senior author. 

When alien plants integrate into an existing ecosystem and successfully spread, in rare cases this contributes towards the uniqueness of regional flora.

However, it is more often the case that it naturalises, leading to a decline in diversity.  

JAPANESE KNOTWEED HAS BAMBOO-LIKE STEMS AND SMALL WHITE FLOWERS

Japanese Knotweed is a species of plant that has bamboo-like stems and small white flowers.

Native to Japan, the plant is considered an invasive species. 

The plant, scientific name Fallopia japonica, was brought to Britain by the Victorians as an ornamental garden plant and to line railway tracks to stabilise the soil.

It has no natural enemies in the UK, whereas in Asia it is controlled by fungus and insects.

In the US it is scheduled as an invasive weed in 12 states, and can be found in a further 29.

It is incredibly durable and fast-growing, and can seriously damage buildings and construction sites if left unchecked.

The notorious plant strangles other plants and can kill entire gardens. 

Capable of growing eight inches in one day it deprives other plants of their key nutrients and water. 

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