Can gardeners identify ‘future invaders’?

It is estimated that there are 30 million gardeners in Britain, who could play a crucial role in being the ‘first contact’ for reporting ornamental plants in gardens with invasive potential. Invasive species are one of the five drivers of the global nature crisis, many of which were originally introduced through ornamental horticulture. Ornamentals confined to gardens and those which have already naturalised, but are not yet shown to be invasive, represent a ‘pool’ of species with invasive potential – ‘future invaders’. An online survey asking gardeners to report ornamentals they had noticed invading or taking over their garden resulted in 251 different taxa being reported (including cultivars). The future invaders were prioritised with a simple yet structured scheme, looking at the domestic and global naturalised and invasive status of each taxon, including in the Global Register of Introduced and Invasive Species (GRIIS) and the Global Naturalized Alien Flora (GloNAF) databases. The structured scheme identified a shortlist of nine ornamentals of concern which should be prioritised for further analysis, such as a formal risk assessment. Identifying and preventing future invaders before they escape gardens is critical, to prevent future threats to nature. There is also a gap in the identification of potentially invasive ornamentals, which are not currently invasive, yet are beyond the scope of formal horizon scanning because they are naturalised. Here we explore whether surveying gardeners can be a suitable approach to prioritising future invaders while also being an opportunity to increase awareness of invasive species. This positive feedback loop between gardeners and invasion scientists could help reduce the risk of future invaders.