Tree composition and stand structure in the habitats of a rare tree species, Acer pycnanthum, with special reference to the human impact

摘要

Twenty-nine stands covering almost all Acer pycnanthum habitats in Gifu, Nagano and Aichi prefectures in central Japan were investigated to clarify their tree composition and stand structure. Stands including A. pycnanthum were classified into five major types according to tree composition; each type was characterized by the dominance of Quercus serrata (Type A), Cryptomeria japonica (Type B), A. pycnanthum (Type C), Chamaecyparis pisifera (Type D) and Alnus japonica (Type E), respectively. Types A and E were composed of post-harvest secondary-growth broadleaf stands and Type B was composed of coniferous plantations. Type C included both old-growth without any records of loggings and post-harvest secondary-growth broadleaf stands. Type D was both old-growth and secondary-growth of C. pisifera stand. A. pycnanthum showed the various types of dbh distribution, affected by the land-use history. The tree composition of old-growth stands was supposed to have retained the features of natural A. pycnanthum habitats. As well as strict conservation of existing natural habitats, new habitats must also be created to maintain the population of this species. The expansion and linking of existing habitats is also necessary in order to maintain the local population.