Non-native plants add to the British flora without negative consequences for native diversity

TY - JOUR

T1 - Non-native plants add to the British flora without negative consequences for native diversity

AU - Thomas, Chris D

AU - Palmer, Georgina

N1 - © 2015, The authors. Published by National Academy of Sciences. This is an author produced version of a paper published in Proceedings of the National Academy of Sciences. Uploaded in accordance with the publisher's self-archiving policy.

PY - 2015/4/7

Y1 - 2015/4/7

N2 - Plants are commonly listed as invasive species, presuming that they cause harm at both global and regional scales; ~40% of species listed as invasive within Britain are plants. Yet invasive plants are rarely linked to the national or global extinction of native plant species. The possible explanation is that competitive exclusion takes place slowly, and that invasive plants will eventually eliminate native species (the ‘time-to-exclusion hypothesis’). Using the extensive British Countryside Survey Data, we find that changes to plant occurrence and cover between 1990 and 2007 at 479 British sites do not differ between native and non-native plant species. Over 80% of the plant species that are widespread enough to be sampled are native species, and hence total cover changes have been dominated by native species (total cover increases by native species are over nine times greater than those by non-native species). This implies that factors other than plant ‘invasions’ are the key drivers of vegetation change. We also find that the diversity of native species is increasing in locations where the diversity of non-native species is increasing, suggesting that high diversities of native and non-native plant species are compatible with one another. We reject the ‘time-to-exclusion hypothesis’ as the reason why extinctions have not been observed, and suggest that non-native plant species are not a threat to floral diversity in Britain. Further research is needed in island-like environments, but we question whether it is appropriate that over three-quarters of taxa listed globally as invasive species are plants.

AB - Plants are commonly listed as invasive species, presuming that they cause harm at both global and regional scales; ~40% of species listed as invasive within Britain are plants. Yet invasive plants are rarely linked to the national or global extinction of native plant species. The possible explanation is that competitive exclusion takes place slowly, and that invasive plants will eventually eliminate native species (the ‘time-to-exclusion hypothesis’). Using the extensive British Countryside Survey Data, we find that changes to plant occurrence and cover between 1990 and 2007 at 479 British sites do not differ between native and non-native plant species. Over 80% of the plant species that are widespread enough to be sampled are native species, and hence total cover changes have been dominated by native species (total cover increases by native species are over nine times greater than those by non-native species). This implies that factors other than plant ‘invasions’ are the key drivers of vegetation change. We also find that the diversity of native species is increasing in locations where the diversity of non-native species is increasing, suggesting that high diversities of native and non-native plant species are compatible with one another. We reject the ‘time-to-exclusion hypothesis’ as the reason why extinctions have not been observed, and suggest that non-native plant species are not a threat to floral diversity in Britain. Further research is needed in island-like environments, but we question whether it is appropriate that over three-quarters of taxa listed globally as invasive species are plants.

KW - alien

KW - biodiversity

KW - conservation

KW - invasive species

U2 - 10.1073/pnas.1423995112

DO - 10.1073/pnas.1423995112

M3 - Article

SN - 0027-8424

VL - 112

SP - 4387

EP - 4392

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

IS - 14

M1 - 201423995

ER -