Fig. 3. Mean soil pH, soil aluminum content, and soil iron content. Shown from urban (n = 8) and nonurban (n = 5) sites are: (a) mean soil pH, (b) mean soil Al content, and (c) mean soil Fe content. Dots indicate range of variation; whiskers indicate 5th and 95th percentiles; solid lines indicate median values; and dashed lines indicate means. Means between urban and nonurban samples were significantly different for soil pH in the A and B horizons (p < 0.01). Median values between urban and nonurban samples were significantly different (t test) for soil Al and Fe in the A and B horizons (p 0.001) (after Sonoda et al., 2002).