Effect of vegetation switch on soil chemical properties

Soil chemical properties were investigated under four types of forest to evaluate the effect of replacement of tree species on soil chemical properties in the north of Japan. Two sites had undergone a vegetation switch around 1960 from broadleaved to coniferous trees (BC) and coniferous to broadleaved trees (CB), while the other two sites had had no vegetation change and carried broadleaved trees (BB) and coniferous trees (CC). Soil samples from the four sites were analyzed for pH (water, H ₂O), electrical conductivity (EC), total carbon (C) and nitrogen (N) content, exchangeable cations [Ex. calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na)], inorganic nitrogen (Inorg-N), nitrogen mineralization potential, total phosphorus (P), and available phosphate. Most of the soil chemical properties in both the upper (0–5 cm) and lower (5–10 cm) layers at the BC site had lower values than those at the BB site. Values of soil chemical properties in the upper and lower soil layers were similar at the BC and CC sites. pH, Inorg-N, EC, Ex.Ca and Ex.Mg in the upper layer at the CB site were significantly higher than those at CC site, whereas all soil properties at the CB site except for Inorg-N were similar to those at the BB site. In the lower layer at the CB site, values of soil chemical properties except for the C/N ratio were almost the same as those at the CC site, but lower than those at the BB site. The upper soil layer at sites where a vegetation switch had occurred was affected by the current tree species, whereas in the lower soil layer, the effects differed between the different vegetation switch patterns. At the CB site, where the vegetation switch was from coniferous to broadleaved trees, the soil chemical properties in the lower layer remained similar to those at the coniferous site (CC) 50 years after the vegetation switch, while changes in soil properties have occurred following the switch from broadleaved to coniferous trees. The change in soil nutrient content by vegetation switch was considerably affected by change in not only litter quality but also composition of earthworm community. In particular, a combination of epigeic and endogeic earthworms exhibited important roles for nutrient dynamics to the deeper soil layer.