Figure 2: Species richness frequency per plot: a andb , native and alien species respectively at 3 x 3 m grain;c and d , native and alien species respectively at 1 x
1 m grain; e and f , native and alien speciesdifference in richness between grains (Δ9-1)
respectively. The dotted lines show the mean richness values for native
(blue) and alien (red) plants.