Plant species surveys
Within each of the three plots at all 20 sample sites along the three roads, observers record all vascular plant species (including both native and non-native species) and visually estimate vegetation cover and record abundance classes of each species. The detailed sampling protocol is provided in Supporting Information S1 and can also be downloaded from the MIREN website (www.mountaininvasions.org). Taxa should be identified to species level using up-to-date local floras. Before being included in the global database, submitted regional species lists undergo taxonomic harmonization to detect synonyms for the same species in different regions, and to correct spelling problems. This procedure is done by the MIREN data managers, using the R-packages “taxize” (Chamberlain & Szöcs, 2013; Chamberlain et al., 2020) and “WorldFlora” (Kindt, 2020). Firstly, species names are matched with World Flora Online (http://www.worldfloraonline.org), and if not found there, they are searched via the additional databases included in the Taxonomic Names Resolution Service (Boyle et al., 2013). All changes of species names are transmitted to the submitting region for verification or correction, before the dataset enters the global database (Figure 2).
Each taxon should be classified as native or non-native to that region by the participant using local floras and databases. As a general rule, plant species introduced into the country or mountain range after AD 1500 are considered as non-native, although regional deviations are welcome if properly justified. For noteworthy records (e.g. first records or new high/low elevation records of native or non-native species), specimens should be collected outside of the plots (when possible) and placed in a herbarium to facilitate identification and to inform local floras (Walsh & McDougall, 2018).