Figure 4: The significant drivers of alien species richness at the small (1 x 1 m) and large (3 x 3 m) grain, and the difference in alien species richness (Alien Δ9-1) between large and small grain. a . Elevation, b . Northness, c . Presence/absence of Azorella selago (the boxplots show the median and minimum/maximum values, different letters above plots indicate significant differences in mean values between presence and absence ofA. selago at p ≤ 0.05), d . Distance to nearest drainage,e . Geology (different letters above plots indicate significant differences in mean values between the geologies at p ≤ 0.05), andf . Mean temperature. The graphs show the effect of predictors on the response variable after the effect of all the other predictor variables had been considered. Model parameters are shown in Table 1c, d.