Non-native plant species do not pose a risk to native flora, as widely assumed, because impacts are limited to localised areas, a study has suggested.
Data showed that non-native species were unlikely to out-compete native species, which were not widespread enough to have an impact nationally.
However, the study adds that invasive species are problematic in local areas, costing an estimated £1.7bn each year.
The findings appear in the Proceedings of the National Academy of Sciences.
The team from the University of York looked at data from almost 500 plots across the UK, comparing results from 1990 with those from 2007. The dataset, the Countryside Survey, is described as a “unique study or audit of the natural resources of the UK’s countryside” and has been collecting data since 1978.
Co-author Chris Thomas from the University of York said the study assessed the impact of non-native species on a national scale, not the impact recorded in localised areas.
“If you look at just one place, there are only going to be certain plants growing there,” he explained.
“If there is a bunch of non-native or recently introduced species growing there then, inevitably, in that exact location you might not see quite as much of what you would regard as native species.
“Locally, it is clearly true that if a non-native species becomes extremely abundant then you’d think that native species were suffering but what we are arguing is that non-native plants are no different from the native ones because, over a period of time, native plants change their abundance as well.”