ヒバ林伐採による土壌有機物の変化について

抄録

Fine stands of "Hiba" (Thujopsis dolabrata var. Hondai MAKINO) are widely distributed in the Tsugaru and the Shimokita Peninsulas, north Japan. Since the tolerance to shade is strong, dense pure stand appears and a large quantity of acid humus accumlates, the writer believes that "Hiba" is one of the podzol-forming species. Accordingly, in the "Hiba" forest region, it is considered that vegetational factor has a great influence on soil formation. Ever since 1957, the writer examined the effect of forest cutting on the soils of moderately moist brown forest (BD), dried brown forest (BB) and podzolized soils (PDIT). In this paper, based on the results during three years after clear-cutting, the changes of contents and nature of soil organic matter were studied. The changes of soil organic matter and related some properties are as follows: 1) The changes of morphology of Aclayer (Fig. 2); Owing to the cutting of "Hiba" forest, the following facts are observed: on BD-soil poor in A_0-layer, F-layer is smashes into fine pieces, and on BB-soil of mor type humus, the thickness of Aclayer reduces to half, H-layer transforms into HA-layer and so appearance of mor type disappears in the third year after cutting, and on PDII-soil the thickness reduces to half, but the appearance of mor type humus remains unchanged. 2) The changes of contents and nature of soil humus (Figs. 3-6); From the analytical results of total carbon and alkali soluble humus on BD-, BB- and PDII-soils, it is found that on BD-soil humus contents immediately diminish after cutting and reduce to minimum in the second year, on BB-soil increase in spring of the second year and hastily decrease in autumn of the same year and gradually increase from that time onward, and on the contrary, on PDII-soil alkali-soluble humus remarkably increases owing to the cutting. From the above mentioned, the writer found that effect of the cutting is greater in order of PDII-< BB- <BD- soils. While on BD-soil poor in Aclayer, organic matter diminishes immediately owing to the cutting, on BB-and on PDii-soils rich in Aclayers, alkali-soluble humus increase momentarily and then gradually decrease with passage of time. Such tendency is especially remarkable on PDII-soil. In view of the above, it is found that Aclayer serves as a buffer which protects the change of soil from environmental changes. Since the forest management is a repetition of deforestation and regeneratoin, the writer considers that such investigation is significant to soil formation and application of soils in forestry.