Abstract
Effects of a mixture of deciduous broad-leaved trees on the understory vegetation and soil properties were investigated in Japanese black pine stands at a coastal sand dune in Kaetsu District, Niigata Prefecture, Japan. The coverage of both shrub and herb layers in the mixed stands was lower than that in the pure pine stands. However, the mixed stands contained many saplings or young growth of evergreen broad-leaved trees compared with the pine stands. Gramineous species which mainly preferred sands or grasslands showed a high coverage in the pine stands, whereas mixed stands contained many forestal species. These results indicated that the mixture of deciduous broad-leaved trees altered light and soil conditions on the forest floor. All soils had a horizon sequence of A0-A-C, which were determined as Sandy immature soil. In the A0 horizon, exchangeable Ca and Mg concentration, base saturation and pH were higher in the mixed stands than those in the pine stands. In the mixed stands, many more nutrients, especially Ca, Mg and N were accumulated in the upper mineral soils (010 cm depth) compared with the pine stands. A mixture of deciduous broad-leaved trees and succeeding establishment of evergreen broad-leaved trees in the pine stands at coastal sand dunes may play a significant role for the conservation and improvement of coastal forests and the reduction of the degree of disaster in these areas.
