Canonical Correspondence Analysis (CCA) for a nutrient-poor sites with P. serotina (n = 47 plots) b nutrient-rich sites with P. serotina (n = 48 plots) c nutrient-poor sites with R. pseudoacacia (n = 48 plots) d nutrient-rich sites with R. pseudoacacia (n = 48 plots). Species with a frequency > 20% are labeled. Green arrows and green labels represent environmental variables. Red dots = control plots, light blue dots = plots with P. serotina or R. pseudoacacia. Abbreviations: log1p(Biomass) — natural logarithm of invader aboveground biomass.