The reason why I evaluate Japanese Black Pine as just one among many trees is explained for the disaster prevention of the coastal forest in Japan. This pine, maritime species native in Japan, is big tree growing up to 40 m in height, with long roots growing vertically into soil, evergreen needles and thick bark tolerant against salty sea water, and stout thick trunk called hard pine. This pine is luxuriantly growing on dry and salty sand hill along the seashore by the activity of mycorrhizal fungi. Dense forest of this pine, therefore, has been used in the disaster prevention of maritime sand hills in Japan as just one.

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We studied the need for thinning in the stands of the Nishinohama coastal forest (Tahara city, Aichi prefecture) where Japanese Black Pine (Pinus thunbergii) seedlings regenerated naturally and densely after devastating damage caused by Pine Wilt Disease. We considered the different stage of the stands where the seedlings were regenerated in change over time, because we need time to obtain the result if we pursue the passage of stands. Consequently, although natural thinning was allowed to progress, overcrowding was not mitigated. In other words, the seedlings became extremely overcrowded and the density in terms of the number of trees soared, with five times or more per investigation area compared with the proper number. Accordingly, trees with thin trunks and height/dbh ratios exceeding 100 occupied the majority. Although trees with height/dbh ratios of 70 or less existed, the ratios were less than 15% in almost all investigation areas. Moreover, the number of trees with height/dbh ratios of 70 or less did not approach the proper number density, despite the increased canopy height. Therefore, we expected as follows; when the Japanese black pine stand with seedling densely caused by natural regeneration is left, healthy trees with height/dbh ratio of 70 or less might remain, avoiding failing together but the stand becomes only an open forest, due to insufficient healthy trees to form a closed forest. In other words, thinning is necessary when the closed forest is required at one generation where natural regeneration occurs after the devastating damage caused by Pine Wilt Disease

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The use of water-retaining material and mixing of the soil dressing for planting Kuromatu to increase its survival ratio on a sandy coast was analyzed. Water-retaining material in a dry state was ineffective in increasing the survival ratio of the planted tree. However, when a water-retaining material containing reabsorbed water was used, the survival ratio improved. When seedlings with water-retaining material attached to roots were used, the survival ratio of the planted tree improved. The survival ratio of the planted tree also improved with mixing of the soil dressing. This effect was commonly observed in Akadama and Kanuma soils.

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Coastal forests have a potential to be a defense wall toward not only blown sand but also tsunami attack to the land area, therefore they play quite important role especially in the view of disaster prevention. The authors surveyed the methods of coastal forestation works using a questionnaire delivered to 18 prefectural offices and 5 national forestation offices from north to south in Japan. The results of the questionnaire showed that the forestation methods varies widely over the country between east and west region, e.g. east as along the Pacific Ocean and west as along the Sea of Japan. Also the results notified that there are some methods which are commonly adopted over the regions, it is concluded that such common methods are relatively more important than other biased methods.

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