Establishment of tree seedlings and water-soluble nutrients in coarse woody debris in an old-growth Picea-Abies forest in Hokkaido, northern Japan

Forest floor microsite conditions and tree seedling establishment were stud ied at an old-growth Picea-Abies forest in Hokkaido Island, northern Japan. Tree seedlings were established abundantly on coarse woody debris (CWD) fr om decay class III, a class indicating moderate decay, to class V, the most advanced decay class. The height-class distribution of tree seedlings indi cates that the recruitment of Picea glehnii (Fr. Schm.) Masters and Picea j ezoensis (Sieb. et Zucc.) Carr. seedlings on CWD started on decay class II and was mostly restricted to CWD decay class III. Seedlings of Abies sachal inensis (Fr. Schm.) Masters also favored establishment on CWD but had a wid e adaptability to most of the microsites. Although CWD functioned as a suit able seedbed, water extracts from CWD were acidic and had quite low mineral nutrient concentrations. Tree seedling establishment did not necessarily r equire high levels of nutrient content in microsites. Although the forest f loor was largely covered by CWD, with 2056 m(2).ha(-1) of the total project ed area covered by CWD, CWD decay class III covered only 366 m(2).ha(-1) of the forest floor, indicating that CWD as a functioning seedbed is limited by time and space on the forest floor.