Vegetation, amount of sediment movement and forest floor cover percentage were investigated in five stands with different vegetation condition in “Izumo-Kitayama” mountainous districts of Izumo City, Shimane prefecture, from July 2013 to September 2014. The stand (1) is a forest stand damaged by pine wilt disease immediately before this study. The stand (2) is a forest stand where over 10 years have passed after the damage of pine wilt disease. The stand (3) is a broad-leaved deciduous forest. The stand (4) is a logged area with poor vegetation. The stand (5) is a logged area where forest floor plants are only living. The order of the stands according to the quantity of sediment movement is (4)>>(5)>(1)>(3)>(2). The sediment movements were inhibited by the high forest floor cover percentage (around 80%) and the low crown of Symplocos kuroki under dead trees of pine wilt disease in (1), by the lowest crown distribution among the five stands and the high forest floor cover percentage (over 90%) in (2), by the high forest floor cover percentage (over 90%) due to falling leaves of Quercus variabilis in (3), by the high forest floor cover percentage (over 90%) due to recovering of forest floor after logging in (5). In stand (4) with poor vegetation, sediment was severely moved. The stand (2) and (3) had the lowest sediment movement as mentioned above. Therefore, the two stands were thought to be one of the target forest in “Izumo-Kitayama” mountainous district. In stand (5), sediment movement was inhibited during the study. But, the possible increase of browsing by sika deers as the number of sika deers grows cause a large quantity of sediment movement, as in stand (4). In logged areas such as (4) and (5), it is necessary to regenerate the woody plants which form crowns and can supply deciduous leaves.

As trees increase in size, water transport from roots to leaves becomes constrained due to increasing path length, hydraulic resistance, and hydrostatic limitation. In trees, hydraulic conductivity decreases with increasing size due, not only to hydrostatic constraints and increasing path length, but also increasing number of annual nodes and junctions through which water must travel to reach terminal leaves. Axial tapering of xylem conduits contributes to increasing efficiency of whole-tree water conduction and minimizing hydraulic constraints on productivity and growth. Here, we compared xylem structure along the vertical gradient in large, old Cinnamomum camphora trees (with height ca. 25 m and age ca. 100 years) to infer the height effect on xylem structure and its variation with height. Vessel diameter (D) was smaller and vessel density per sapwood area was higher for upper than lower trunk. Within annual rings, vessel diameter decreased from early- to late-wood and the rate of this change was nearly constant with height. Potential hydraulic conductivity, calculated from D, was markedly lower for upper than lower trunk and lack of vessels with D > 250 μm at upper trunk contributed to this difference. Vertical change in xylem structure observed here, may contribute to maintaining hydraulic efficiency and minimizing hydraulic limitation in large, old trees.