Native Flora Not Threatened by Introduced Species

When it comes to plant life in Britain, it is generally thought that species introduced from other countries - "non-native species" - pose a risk to the plants that originate here. But according to University of York study that has recently been published in PNAS , these plants aren't quite as invasive as we thought. Not only are plants that have been introduced to Britain less widespread than native species, they're also not spreading any quicker either. In fact, the report indicates a positive association between the two; areas in which native species thrive, so do non-native plants, and vice versa. So where did the assumption that non-native plants are a problem for native flora come from? It could be something to do with localised studies. So, instead of localising their research, the team led by Professor Chris Thomas and Dr Georgina Palmer wanted to assess the impact of introduced species on a national scale. They collected data from around 500 different sites across the UK, in 1990 and again in 2007, and then compared and analysed the results. Professor Thomas and Dr Palmer, both authors of the report, explained that examining data on a local scale could give the wrong impression. If a non-native species is particularly abundant in one area, it would be plausible to think that native plants were suffering. But it could simply be a case of the land being more suitable for the foreign plant and the native species could be flourishing somewhere else. The professor used bramble for his example. "[They] might become abundant," he said, "or a change in uplands management could result in bracken becoming more widespread." During the report's time frame, native species were also shown to have increased their abundance more so than non-native flora. On top of this, most introduced species were not even common enough to show up at any of the study sites. This means that, despite popular belief, most of the vegetation in the UK is actually made up of native plants. Any changes to the vegetation doesn't have anything to do with the introduction of new species. The study didn't give the team the predicted results of new species increasing and native species decreasing. Instead, they found that there wasn't any consistent different between the species, regardless of when they arrived in the country, or they were already here. The team therefore concluded that there are lots of non-native plant species on the list of problematic plants for no reason. And as Professor Thomas suggested, it doesn't make any real sense, "unless you are willing to add hundred of problematic native species to the list as well."