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

It is acknowledged that exogenous nutrient addition often stimulates early-stage litter decomposition in forests and late-stage decomposition is generally suppressed by nitrogen addition, whereas the interactive effects of nutrient addition and abiotic environmental factors, such as climate, on decomposition remain unclear. The tea bag method, which was developed to provide the decomposition rate constant k of early-stage decomposition and stabilization factor S of labile materials in the late stage, is a potentially useful tool for examining the impacts of nutrient addition on both early- and late-stage litter decomposition and their interactions with climate. At a long-term (38-year) continuous fertilization experimental site (an Abies sachalinensis Fr. Schmidt stand) in Hokkaido, Japan, we examined whether a standard tea bag method protocol was sufficiently sensitive to reveal any impacts of nutrient addition on early- and late-stage decomposition. In addition, we tested the interactive effects of nutrient addition and climate on litter decomposition. The short incubation period of the tea bag method (ca. 90 days) enabled us to obtain decomposition data from the same location at three different times in a year, i.e., early summer, midsummer, and winter, providing an opportunity to test interactive effects. We demonstrated that the decomposition rate of rooibos tea and the decomposition rate constant k of early-stage decomposition were clearly stimulated by fertilization in midsummer, but no impacts were detected in other seasons, probably because the relative importance of nutrient availability was elevated in midsummer, during which decomposition rates were less constrained by temperature and moisture. The green tea decomposition rate and stabilization factor S, an index related to late-stage decomposition, were unaffected by fertilization. This was probably because the tea bag method does not take into account lignin degradation, which is considered a key factor controlling late-stage litter decomposition. Overall, the present study (i) successfully determined the interactive effects of nutrient addition and climate factors on litter decomposition by making full use of the tea bag method, and (ii) the results suggest that the tea bag method can be a suitable tool for examining the direct effects of nutrient addition and their interactions with environmental factors on early-stage litter decomposition, but not those on late-stage decomposition.

Estimating carbon (C) and nitrogen (N) stocks in deadwood in forests nationwide is required for understanding large-scale C and N cycling. To do so requires estimated values of wood density and C and N concentrations. Additionally, parameters that show variation should be examined. In this study, we clarified the estimated values and the variation in three parameters in each decay class of each of two tree species and examined whether dead log diameter and region contribute to variation in the parameters. Data were collected from 73 Chamaecyparis obtusa (Sieb. et Zucc.) Endl. plantations and 66 Cryptomeria japonica D. Don plantations throughout Japan. Wood densities decreased from 386 to 188 kg m À3 for C. obtusa and from 334 to 188 kg m À3 for C. japonica in decay classes 1-4. The variation in wood density increased with decay class, and the coefficient of variance increased from 13.9% to 46.4% for C. obtusa and from 15.2% to 48.1% for C. japonica. The N concentrations increased from 1.04 to 4.40 g kg À1 for C. obtusa and from 1.11 to 2.97 g kg À1for C. japonica in decay classes 1-4. The variation in N concentration increased with decay class, and the coefficient of variance increased from 51.9% to 76.7% for C. obtusa and from 50.3% to 70.4% for C. japonica. Log diameter and region contributed to variations in wood density and N concentration in decay classes 1 and 2 for C. obtusa and C. japonica. However, no relationship was observed between regional climates and the two parameters. In contrast, C concentrations ranged from 507 to 535 g kg À1 and were stable with much lower coefficients of variance throughout the decay classes for both tree species. Thus, we recommend that the same C concentration can be adapted for all decay classes of both tree species.

The tea bag method provides a replicable and standardized method to study the effect of environmental variables on the decomposition of standard litter, which enables comparison of organic matter decomposition rates on a large scale. However, it remains uncertain whether tea bag decomposition in response to wetness is representative of that of local litters. We performed incubation experiments to examine whether the effect of soil water on tea bag decomposition becomes inhibitory at higher water contents, as is the case in local leaf litters. In addition, we performed field studies in a mixed forest and cedar plantation in Japan to compare two litter bag mesh sizes: 0.25-mm mesh, the size previously used by a major manufacturer of tea bags (Lipton), and nonwoven bags with mesh sizes finer than 0.25 mm, which are currently produced by Lipton. Both green tea and rooibos tea exhibited higher decomposition rates at higher water contents, but decomposition was inhibited at the highest water content; this was in contrast to our hypothesis based on a field observation but consistent with conceptual models of local litters. The nonwoven tea bags did not show lower decomposition rates, despite the finer mesh size. Rather, the nonwoven rooibos tea bags exhibited slightly higher decomposition rates than the 0.25-mm mesh bags in the cedar plantation, possibly due to a greater abundance of microorganisms that decompose litters in the nonwoven bags, due to the decrease in predation by mesofauna. Our findings provide essential information for future studies of tea bag decomposition.