Supplementary Information

S1 File. Supplemental information: methods and results. Detailed history of management for both Reference sites and methods for data analysis, including the list of R packages used. All supplemental results (Table A-J and Fig A-D) are also included. A glossary for site, plot and treatment numbering is included.

S2 File. Species list from NIRMI plant survey at BM and VV Slag. “1” denotes presence. C-value stands for Coefficient of Conservatism, based on Universal FQA Calculator.

S3 File. Species presence/absence for each plot. Data were compiled from three days of observation: day 77, 91 and 112. Positive identification of a species at any of these days counts as presence, marked by “1”. Two unidentified Dicanthelium species are marked with *. Species only appeared in topsoil plots are marked with ‡; species germinated from the commercial topsoil in the greenhouse are marked with †.

S4 File. Functional traits of plant species observed in the survey used for data analysis. Species abbreviations follow those used in S3 File. If one species has multiple measurements of one single trait, measurements were either averaged (numerical) or entered together (categorical). Numerical data with multiple measurements were averaged. Missing data were left blank and substituted with NA in actual analyses. For all analyses, “Type”, “Growth Form” and “Native?” were taken out; in addition, “Seedbank Longevity” and “Lateral Spread” were taken out when performing RLQ analysis and fourth-corner method because of low availability of data. Data were unavailable for the two unidentified Dicanthelium species and Cyperus bipartitus.

S5 File. Cover data. Cover in all removal and control plots is measured from weekly monitoring photos. Time is in days from start of the experiment.

S6 File. Species number over time. Species number over the full experimental period in each removal and control plots is obtained from weekly monitoring photos. Time is in days from start of the experiment.

S7 File. Biomass of germination plots. Biomass of removal and control plots at the end of experimental period.

S8 File. Initial biomass of focal species plots. Biomass of focal species plots at the beginning of experimental period (week 2 after planting).

S9 File. Final biomass of focal species plots. Biomass of focal species plots at the end of experimental period.

S10 File. Reference sites species list. Species lists were compiled from Chicago Park District seeding plans for BM-R and plant survey on VV-R. Note that these lists were not obtained by the same method used for Slag sites.