Dataset compilation
For all datasets, all plant species names were standardized using the canonical name from the Catalogue of Life using the taxize package in R (Chamberlain & Szocs, 2013). Additionally, for approximately 80% of the plant species, we obtained their evolutionary strategy (Grime, 1979), Landolt’s Ecological Indicator Value for Temperature (EIV-T; Landolt et al. 2010), and their native status (Weidema, 2000; a compilation of information and databases on introduced species in Nordic areas). EIV-Ts are useful indices to reflect the environmental temperature where a plant species is most likely to sustain a population. They range from 1 to 5 (1 = cold-loving and 5 = warm-adapted; Landolt et al. 2010), therefore providing a one-dimensional broad-scale temperature niche for each species. A species was identified as at least partially ruderal when its Grime’s CSR strategy classification (C: Competitive, S: Stress-tolerant, R: Ruderal) contained an R, e.g., CRS, CRR, or RRR (Grime, 1979).
Of the 401 observed species in the combined historical dataset, 240 were identified as ruderal and 100 were identified as non-native ruderals. The Rallarvägen 2021 resurvey dataset contained 268 species of which 94 were identified as ruderal and 36 were identified as non-native ruderals. The MIREN T-trails dataset contained 128 species of which 39 were identified as ruderal and 12 were identified as non-native ruderals. We managed to obtain the EIV-T for every identified ruderal species.