Effects of mean maximum tree height in 91 ecological sections on the degree to which PSC (A) and PSV (B) affect invasive species cover (i.e. slope values for these relationships). Note that values on x and y axes were transformed (z-transformed and [(x + abs(min(x)) + 1)7], respectively) prior to analysis. Untransformed values for slopes were largely negative (Fig. 1; Suppl. material 3, fig. S3.1)