Evaluation of a natural forest restoration project in Kobe City, Japan ten years after planting

Abstract

Among the various methods of forest restoration in Japan, restoration of mid-successional, secondary forests, which have high biodiversity, could contribute to maintaining biological diversity in human-disturbed landscapes. In many restoration projects, the neighboring natural secondary forest is often chosen as the target vegetation. However, there is no established methodology for secondary forest restoration in Japan. Here, we compared tree species composition and stand structure between a restored site (10 years after planting) and the neighboring secondary forest designated as the target vegetation. We found that restoration contributed to increasing tree cover, but the vertical structure of the stand was poorly developed. Moreover, the species composition of the neighboring secondary forest had changed markedly in ten years, mainly due to pine-wilt disease. As a result, compositional similarity between the restored and target plots had not increased in 10 years, while structural similarity was lower than 10 years ago. We conclude that, although current forest restoration methods contribute to increasing vegetation cover, single plantings of native species may be insufficient to restore the natural community structure, especially because vegetation of the target forest is constantly changing. Subsequent adaptive management is needed to direct succession of restoration sites toward natural forest composition and structure.