SDG 15: TARGET 15.8: screening of botanic garden collections for invasive species: a case study from Germany.
Botanical gardens (BGs) play an important role in plant conservation, research and public outreach. Living collections of BGs may also provide a source of invasive species because they harbour a high number of wild plants originating from all over the world. In European BGs for example the current number of cultivated species is estimated to be c. 80 000. In the past, a number of plant species have escaped botanical garden collections and became naturalized in the wild. To reduce the threats from invasive species becoming naturalized outside BGs Heywood and Sharrock (2013), through the Council of Europe, published a European Code of Conduct for Botanic Gardens on Invasive Alien Species; this document is not legally binding but suggests voluntary measures. Among them it proposes to "undertake an audit of the existing collections in the botanical garden for invasion risk". This paper presents an evaluation of the invasiveness of plant species grown outdoors in 20 German BGs and two in neighbouring countries. The aim was to (i) identify those species that are known as invasive in whatever region of the world, and (ii) to identify amongst these, species that do not grow wild in Germany but which have aclimatic match between their native ranges and Germany, thus are likely to be able to spread into suitable habitats. These can be considered as species potentially invasive to Germany and requiring special attention. The study showed that screening the collections in BGs is feasible and worth conducting in order to help reduce the threats by invasive plant species. Such an approach also helps to highlight that the majority of cultivated species do not have the risk of becoming invasive.