Figure 18.5 A line transect of serpentine and nonserpentine soils. As one moves along the transect, the concentration of metals in the soil exhibits a sharp increase midway along the transect. The presence of plant species along the gradient, as indicated by the bars, demonstrates that some species primarily live in nonserpentine soils (shown in blue), a few species primarily live in the ecotone (shown in green), and several species primarily live in the serpentine soils (shown in pink). Three of the species are able to live across the entire transect (shown in purple).
Data from C. D. White, “Vegetation–Soil Chemistry Correlations in Serpentine Ecosystems” (Ph.D. dissertation, University of Oregon, 1971).