Surface Soil pH Decrease under Sugi (Cryptomeria japonica D. Don) Trees on the Lowland in the Kinki District

Abstract

Recently, decline of Sugi trees has been reported on the lowland in the Kinki District. To investigate the cause of the decline, we analyzed degree of Sugi decline and surface soil acidity under Sugi trees in 1987-1991. Studied sites were 274 shrines or temples. And in each site we investigated Sugi trees of old age (over 80 years old) and collected surface soil samples under Sugi trees. Soil pH was measured by means of the glass electrode pH meter.
In some sites surface soils close to trees were very acidic (pH values were below 4.0). In most sites there was a tendency that soil pH value around the stem was lower than that among trees. But there was no correlation between the degree of Sugi decline and the soil acidity.
We also analyzed surface soil acidity under other species, Hinoki (Chamaecyparis obtusa), Akamatsu (Pinus densiflora), Kuromatsu (Pinus thunbergii), Kusunoki (Cinnamomum camphora) and Konara (Quercus serrata). The soil pH was lower in the following order, Hinoki sites<Akamatsu and Kuromatsu sites<Kusunoki and Konara sites. Particularly in Hinoki sites soil pH values around stems were lower than those among trees as in Sugi sites. This pH decrease around the stem is probably correlated to stemflow. We measured the pH of leachates from bark of each tree species. The pH value was lower in the following order, Sugi and Hinoki<Akamatsu and Kuromatsu<Kusunoki and Konara.
These results suggested that the stemflow acidity is specific to the species, and that the acidity of surface soil around stem has been influenced by stemflow. The low surface soil pH around Sugi stems might be a result of the acidic stemflow, and might not be the cause of the decline.