Coastal forests that were entirely washed away by the 2011 Tohoku earthquake and tsunami turned into driftwood, increasing the tsunami damage. It is desirable that coastal forests should not be washed away by a tsunami even if they are knocked down. Using Google Earth images and 10-m mesh land elevation data, we investigated the relationship between types of forest damage (washed away or not) and topography in 17 coastal forests that were attacked by tsunamis of 6-16 m in height. In case of a tsunami height of <10 m, either a ground elevation of >3 m at the front of the forest, or an elevation of >1.2 m at the front and an elevation of >2 m at the rear of the forest was essential for coastal forests to not be washed away. In case of a tsunami height of >10 m, 4 factors were important for coastal forests to not be washed away : a ground elevation of >2 m at the front of the forest, a distance of >130 m from the shoreline to the forest, a forest width of >190 m between the front and the rear of the forest, and a ground slope steeper than 0.085 mm^-1 from the front to the rear of the forest. These findings can be applied to new countermeasures against anticipated Nankai Trough large-scale earthquakes and tsunamis.

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After the 2011 Great East Japan tsunami, assessments of the role of coastal forests as natural defenses against tsunamis are strongly needed. To increase the reliability of such assessments, we conducted flume experiments using living branches of Pinus thunbergii that is main species in the coastal forests of Japan and measured the hydraulic characteristics of Pinus thunbergii. The drag coefficients of leaves decrease with increasing flow velocity in velocities less than 1.2m is and do not have an obvious relation to the flow velocity for velocities greater than 1.2 m/s. This may be because leaf deformation does not indefinitely increase as the flow velocity increases. Therefore, it is suggested that the drag coefficient of leaves converges with increasing flow velocity. For flow velocities greater than 1.2 m/s, the average drag coefficient of leaves is 0.013. The drag coefficients of branches do not have an obvious relation to the flow velocity and the average drag coefficient of branches is 0. 78.

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Apart from the well-known ecosystem services of mangroves in the coastal regions, mangroves recently have been recognized as a major repository of carbon. However, little is known about the carbon storage in the mangroves as soil aggregates and, we envisage that studying soil aggregates under mangroves in comparison with upland forest soil aggregates would yield valuable information about the process of carbon storage. Therefore, this study aims to elucidate comparatively, the characteristics of soil aggregates of mangrove and upland forest soil, separated by density fractionation. Samples were collected from a mangrove ecosystem and an upland forest area in the northern region of Okinawa Island. Four density fractions (<1.6, 1.6～2.0, 2.0～2.5 and >2.5 g cm^-3 fractions) were separated by sodium polytungstate with three density levels (1.6, 2.0 and 2.5 g cm^-3). Carbon and nitrogen content and C/N ratio were highest in the lighter fractions and decreased with increasing density. Clay and silt minerals and sand and silt minerals were included in the low-density fractions (<1.6, 1.6～2.0 g cm^-3) and high-density fractions (2.0～2.5 and >2.5 g cm^-3) respectively. In the upland forest soil, highest clay and carbon percentages were observed in the 1.6～2.0 g cm^-3 fraction. However, mangrove soil had the highest carbon content in the 1. 6～2.0 g cm^-3 fraction, which, on the contrary, had low clay content. Therefore, it can be suggested that clay minerals are necessary to stock carbon in the upland soil. However, it was not the case for the mangrove soil.

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Many trees of coastal forests in East Japan were damaged by the Great East Japan tsunami. Since then, the restoration of coastal forests damaged by the tsunami has been in progress. Therefore, the evaluation of the lodging resistance characteristics of the trees of coastal forests is strongly required, but these characteristics have been insufficiently studied for broad-leave tree species. We conducted tree-pulling experiments on Pinus thunbergii and the following broad-leaved tree species of coastal forests : Acer mono var. glabrum, Machilus thunbergii, Quercus crispula, Quercus dentata, and Zelkova serrata. The diameter at breast height(dbh) of the experimental trees ranged from 5 to 15 cm. For each tree species, the critical turning moment at which tree was uprooted increased with the increasing tree size characteristics such as dbh, squared dbh x tree height(dbh²h), and weight of above ground parts of tree (w). The critical turning moment of each tree species was well approximated by the functions of dbh, dbh²h, and w. The critical turning moment of Z. serrata was the largest and that of M. thunbergii and P. thunbergii were the smallest among the six tree species studied.

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ケヤキ、エゾイタヤ、カシワ、シナノキの4種類の落葉広葉樹をクロマツと混交させるための植栽方法を検討した．クロマツ幼齢林内に試験区を設け，広葉樹植栽区（以下「広葉樹区」），クロマツと広葉樹を植栽したクロマツ同齢混交植栽区（「マツ同時区」），予め2年前にクロマツを植栽し，後で広葉樹を植栽したクロマツ異齢混交植栽区（「マツ先行区」）の3区で比較を行った．植栽区間では広葉樹の生存率と樹高成長量に差がなかったが，マツ同時区ではクロマツと広葉樹が同じ階層で競合しており，クロマツが被圧される可能性が考えられた．また樹種間ではケヤキが生存率，成長量ともに優れていた．今回の結果からクロマツと広葉樹を競合させないように二段林化を図る場合には，クロマツを先行的に植栽し，その後に広葉樹を植栽する異齢二段林が有効と考えられた．

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