Plants like Japanese knotweed are causing flowers across the UK to lose their uniqueness
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.
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.'
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.