Control of invasive alien weeds averts imminent plant extinction

Invasive alien species constitute a major threat to biodiversity and cases of extinction caused by invasive alien animals are abundant. However, while invasive alien plants also harm native biota there exists a lack of cases demonstrating their ability to cause extinction of native plant species. Different alien species (vertebrates, invertebrates, pathogens etc.) commonly deliver different simultaneous impacts like predation, disease or competition. In such situations, assessing the contribution of plant invasion in causing decline of a given plant population in its natural habitat can be difficult, yet is desirable to avoid or minimize wastage of managers' resources. Using native angiosperms in lowland wet forests of Mauritius, we first compared native seedling diversity in forest areas that have been weeded of invasive alien plants about a decade previously, with adjacent similar but non-weeded areas. Then, using the weeded area, we compared results of native plant surveys carried out around the time that invasive alien plants were controlled, with the same community about a decade latter. Species richness and abundance of seedlings were higher in the weeded areas compared to the adjacent non weeded forest. We also found that several species that were presumed extinct or critically threatened with extinction had recovered dramatically as a consequence of the sole removal of invasive alien plants. This shows that the threat posed by invasive alien plants can be overwhelmingly important in driving native plant population declines in tropical forests and that imminent plant extinctions can be averted by timely control of alien plants.