Forest floor microsite conditions and tree seedling establishment were studied at an old-growth Picea-Abies forest in Hokkaido Island, northern Japan. Tree seedlings were established abundantly on coarse woody debris (CWD) from decay class III, a class indicating moderate decay, to class V, the most advanced decay class. The height-class distribution of tree seedlings indicates that the recruitment of Picea glehnii (Fr. Schm.) Masters and Picea jezoensis (Sieb. et Zucc.) Carr. seedlings on CWD started on decay class II and was mostly restricted to CWD decay class III. Seedlings of Abies sachalinensis (Fr. Schm.) Masters also favored establishment on CWD but had a wide adaptability to most of the microsites. Although CWD functioned as a suitable seedbed, water extracts from CWD were acidic and had quite low mineral nutrient concentrations. Tree seedling establishment did not necessarily require high levels of nutrient content in microsites. Although the forest floor was largely covered by CWD, with 2056 m 2 ·ha -1 of the total projected 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.Résumé : Les conditions dans les microsites du parterre forestier et l'établissement des semis d'arbre ont été étudiés dans une vieille forêt de Picea-Abies sur l'île d'Hokkaido, dans le nord du Japon. Les semis étaient abondants sur les débris ligneux grossiers dans la classe de décomposition III, une classe qui indique une décomposition modérée, à la classe de décomposition V, la classe de décomposition la plus avancée. La distribution des classes de hauteur des semis montre que le recrutement des semis de Picea glehnii (Fr. Schm.) Masters et de Picea jezoensis (Sieb. et Zucc.) Carr. sur les débris ligneux grossiers a débuté avec la classe de décomposition II et était surtout limité à la classe de décom-position III. Les semis de Abies sachalinensis (Fr. Schm.) Masters s'établissaient surtout sur les débris ligneux grossiers mais s'adaptaient à la plupart des microsites. Bien que les débris ligneux grossiers constituent un lit de germination adéquat, les extraits aqueux des débris ligneux grossiers sont acides et ont une très faible concentration en nutriments minéraux. L'établissement des semis n'exigeait pas nécessairement un contenu élevé en nutriments dans les microsites. Bien que le parterre forestier soit largement recouvert de débris ligneux grossiers, avec 2056 m 2 ·ha -1 de la superficie totale projetée couverte par des débris ligneux grossiers, les débris ligneux grossiers appartenant à la classe de décomposition III couvraient seulement 366 m 2 ·ha -1 du parterre forestier, indiquant que le rôle des débris ligneux grossiers comme lit de germination efficace est limité dans le temps et dans l'espace.[Traduit par la Rédaction] Takahashi et al. 1155

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Root biomass and root distribution were studied in Entisols derived from the thick deposition of volcanic pumice on Hokkaido Island, Japan, to examine the effect of soil conditions on tree root development. The soil had a thin (<10 cm) A horizon and thick coarse pumiceous gravel layers with low levels of available nutrients and water. Two stands were studied: a Picea glehnii-Abies sachalinensis stand (PA stand) and a Larix kaempferi-Betula platyphylla var. japonica stand (LB stand). The allometric relationships between diameter at breast height (DBH) and aboveground and belowground biomass of these species were obtained to estimate stand biomass. The belowground biomass was small: 30.6 Mg ha −1 for the PA stand and 24.3 Mg ha −1 for the LB stand. The trunk/root ratios of study stands were 4.8 for the PA stand and 4.3 for the LB stand, which were higher than those from previous studies in boreal and temperate forests. All species developed shallow root systems, and fi ne roots were spread densely in the shallow A horizon, suggesting that physical obstruction by the pumiceous layers and their low levels of available water and nutrients restricted downward root elongation. The high trunk/root ratios of the trees may also have resulted from the limited available rooting space in the study sites.

Estimation of carbon sequestration in the forest sector should take into consideration changes in carbon stock in all carbon pools, including above‐ground and below‐ground biomass, litter, deadwood and soil. In this review, we discuss current knowledge of carbon stocks in litter, deadwood and soil in Japan’s forest sector. According to data from published reports and nationwide surveys, the carbon stock in forest litter is less than that indicated in the Intergovernmental Panel on Climate Change (IPCC) guidelines for temperate and cool temperate forests; for example, coniferous species showed 4.4 Mg C ha−1 for Cryptomeria japonica and 3.1 Mg C ha−1 for Chamaecyparis obtusa, and broad‐leaved species ranged from 3.5 Mg C ha−1 for Castanopsis spp. to 7.3 Mg C ha−1 for Fagus spp. For deadwood carbon stock, coniferous plantations with a record of non‐commercial thinning showed 17.1 Mg C ha−1 and semi‐natural broad‐leaved forests showed 5.3 Mg C ha−1 on average, although only limited data were available. The black soil group (comparable to Andosols and Andisols) showed large carbon stocks in soil layers 0–30 cm deep (130 Mg C ha−1). The brown forest soil group (Cambisols and Inceptisols), occupying the most dominant area, showed a carbon stock of 87.0 Mg C ha−1 on average, which was similar to the data shown in the IPCC guidelines. In a comparison of land use between the forest sector and the agricultural sector for the same soil group, the carbon stock in the agricultural soil was 21% lower and in the grassland soil it was 18% higher than the stock in the forest soil. In this review, we also discuss issues for improving the estimation method and inventory of carbon stock in litter, deadwood and soil in Japan.

Cryptomeria japonica (sugi) and Chamaecyparis obtusa (hinoki) are major Japanese timber species whose plantation area accounts for 44 and 25%, respectively, of the plantation forests in Japan. Physiology, anatomy and ecology of the species have been intensively studied for this half century, which now forms a huge stock of information. These data, however, were scattered in diverse sources, including papers, bulletins of research institutes, reports of other kinds and books, and were presented in nonstandardized, diverse styles in each source. This paper