Abstract
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
https://ror.org/044bma518 
