Plant responses
Plant species richness decreased with increasing invasion across all
gradients (Figure 1a, Appendix S1: Table S1). Plant community (Figure
2a, Appendix S1: Table S2) and functional (Figure 3a, Appendix S1: Table
S3) composition differed significantly across invasion levels. In
Montana, B. arvensis invasion was negatively correlated with
C3 perennial grass, C4 perennial grass,
forb, and sub-shrub/shrub cover (Appendix S1: Figure S3a, Table S4). In
Wyoming, B. arvensis and B. tectorum cover were strongly
negatively correlated with C4 perennial grass cover and
weakly negatively correlated with C3 annual grass;B. tectorum cover was also negatively correlated with
C3 perennial grass cover (Appendix S1: Figure S3a, Table
S4).