Especially noteworthy is the marked effect of soluble phos- phorus, which is negatively associated with total richness (Fig. 3). This agrees with the results of Janssens et al. (1998) and Fu et al. (2004), who indicated that the threshold of soil phosphorus needed for the development of rich communities is below 10 ppm (compare Fig. 4). Han et al. (1995) report rather low amounts of PO4 in forests dominated by Q. mongolica. This forest type is dominant in Korea and hosts most of its phytodiversity. This means that most forest plant species in Korea are adapted to low-phosphorus envi- ronments. Correlations repeatedly found for phosphorus indicate that its availability limits both productivity and decomposition in late successional stages, whereas nitrogen is a limiting element during early successional stages (Vitousek and Farrington, 1997). Results of long-term studies indicate that the availability of phos- phorus, unlike that of nitrogen, can significantly affect the productivity of competitive plants, and thus diversity (Chytrý et al., 2009).