Thinning alters crown dynamics and biomass increment within aboveground tissues in young stands of Chamaecyparis obtusa

The stand density of a forest affects the vertical distribution of foliage. Understanding the dynamics of this response is important for the study of crown structure and function, carbon-budget estimation, and forest management. We investigated the effect of tree density on the vertical distribution of foliage, branch, and stem growth, and ratio of biomass increment in aboveground tissues; by monitoring all first-order branches of five trees each from thinned and unthinned control stands of 10-year-old Chamaecyparis obtusa for four consecutive years. In the control stand, the foliage crown shifted upward with height growth but the foliage quantity of the whole crown did not increase. In addition, the vertical distribution of leaf mass shifted from lower-crown skewed to upper-crown skewed. In the thinned stand in contrast, the foliage quantity of individual crowns increased two-fold within 4 years, while the vertical distribution of leaf mass remained lower-crown skewed. The two stands had similar production rates, numbers of first-order branches per unit of tree height, and total lengths of first-order branches. However, the mortality rate of first-order branches and self-pruning within a first-order branch were significantly higher in the control stand than in the thinned stand, which resulted in a higher ratio of biomass increment in branch. Thinning induced a higher ratio of biomass increment in foliage and lower in branch. The increased foliage quantity and variation in ratio of biomass increment after thinning stimulated stem growth of residual trees. These results provide information that will be useful when considering thinning regimes and stand management.     

Seasonal and yearly variations in light use and nitrogen use by seedlings of four deciduous broad-leaved tree species invading larch plantations

Several deciduous broad-leaved tree species, differing in leaf phenology, invade larch (Larix kaempferii (Lamb.) Carrière) plantations in Japan. The understory light environment of larch forests changes drastically between the leafy and leafless periods. To determine how the invading seedlings exploit the changing light environment, and if phenological differences reflect the light- and nitrogen-use traits of the seedlings, we measured leaf phenology, seasonal changes in light-saturated photosynthetic rate (P(sat)), leaf nitrogen (N) content (N(area)), chlorophyll/nitrogen ratio (Chl/N), specific leaf area (SLA) and N remobilization rate (NRMR) over 3 years. The mid-successional or gap-phase species, Magnolia hypoleuca Siebold & Zucc., had a short leafy period and high P(sat) and NRMR. In contrast, two late-successional tree species, Prunus ssiori Friedr. Schmidt, which undergoes leaf flush before larch, and Carpinus cordata Blume, which maintains green leaves until frost, both had low P(sat) and NRMR but exploited the opportunity for growth during the period when the larch canopy trees were leafless. Quercus mongolica Fisch. ex Ledeb. var. crispula (Blume) Ohashi, a mid-late-successional species that underwent leaf flush at the same time as the overstory larch, had values of photosynthetic parameters between those of the gap-phase and late-successional species. Among species, M. hypoleuca and Q. mongolica had higher photosynthetic rates and photosynthetic N-use efficiencies. In all species, the relationship between N(area) and P(sat) showed species-specific yearly fluctuations; however, there was no yearly fluctuation in the relationship between N(area) and P(sat) at CO2 saturation. Yearly fluctuations in the N(area)-P(sat) relationship appeared to be induced by changes in SLA and N-use characteristics, which in turn are affected by climatic variations.     

Pore structure and the properties of electric double layer capacitor electrode of bamboo-derived activated carbon prepared by superheated steam

Bamboo-derived activated carbon prepared by superheated steam (BAC) exhibited performance for utilization as an electric double layer capacitor (EDLC) electrode. Pore structure and EDLC performances were investigated by comparison with phenol resin-derived activated carbon (MSP-20), which is commercially available and often used for the purpose. The nitrogen adsorption isotherm showed that BAC had a large BET-specific surface area of 1268 g/m² with a developed pore structure, especially of the mesopore, in comparison with MSP-20. It is considered that inherent ash in bamboo promoted activation, in addition to physical activation by superheated steam. Capacitance per electrode volume (C_V) was 52 F/cm³ with BAC. Because the density of BAC is high (0.78 g/cm³) compared with that of MSP-20 (0.58 g/cm³), sufficient C_V for usage was obtained, although the capacitance per electrode mass (C_M) at 5 mA/cm² itself of BAC (67 F/g) was lower than that of MSP-20 (126 F/g). With IR drop, the resistance value of BAC (9.7 Ω) was lower than that of MSP-20 (10.5 Ω). Especially, the diffusion resistance of BAC disclosed to be smaller than that of MSP-20. These results indicated that BAC produced by steam activation is a promising material with a pore structure suitable for ion transfer in EDLC.     

Effects of a severe typhoon on forest dynamics in a warm-temperate evergreen broad-leaved forest in southwestern Japan

The effects of a typhoon on forest dynamics and the response of major tree species were studied in a warm-temperate evergreen broad-leaved forest in southwestern Japan. The strongest typhoon on record (T9313) passed through this region in 1993. Return periods of typhoons over 30 ms⁻¹ in instantaneous wind velocity and T9313 were estimated to be 2.2 and 104.5 years, respectively. Approximately 10% of all stems suffered some damage from T9313 and annual stem mortality rose from 1.3 to 2.7%. The estimated period that the number of stems would fall below 10% of the initial was four years shorter with T9313-class typhoons than without them. Thus, the disturbance by T9313 was not catastrophic at the site although T9313 was an episodic typhoon. The short-term responses of major tree species to T9313 were classified into four types: 1) blunt-response type with little decrease and recruitment of stems in the DBH ≥ 5 cm class (Distylium racemosum), 2) retreat type with larger decrease than recruitment (e.g. Quercus acuta), 3) sharp-response type with a large decrease and much recruitment (e.g. Cinnamomum japonicum), and 4) advance type with less decrease than recruitment (Eurya japonica). Among the four regeneration types classified by previous studies (climax, light-demanding, subcanopy, and few-sapling), the climax and few-sapling types each showed a specific short-term response, the blunt-response and retreat types, respectively, that explains one aspect of the regeneration strategies of each type. On the other hand, the light-demanding or sub-canopy type showed multiple short-term responses, indicating that each regeneration type contains species with various regeneration strategies. In this paper, I analyzed data from the database that was compiled by the Aya Research Team.     

Long-term growth analyses of Japanese cedar trees in a plantation: neighborhood competition and persistence of initial growth deviations

The individual growth of tree diameter at breast height (dbh) is analyzed in an even-aged plantation of Cryptomeria japonica from stand age of 45 to 94 years, to examine how the growth of individual trees has been affected by the changes in spacing resulting from thinning operations. At any age, a significant proportion (0.37–0.46) of the variation in dbh growth during a 5–11-year period was explained by dbh at the beginning of the period, probably due to greater leaf mass of larger trees. Next, either one-sided or two-sided competition was added to the model, by calculating the basal area (BA) of neighboring trees around each tree within a given radius or BA for trees having larger dbh than the focal tree within the radius. After preliminary analyses, a radius of 8 m was selected as the critical range for tree competition. Although both types of competition explained a significant proportion (0.09–0.43) of growth variation, one-sided competition was not significant at ages greater than 54 years. Based on the model at 45 years of age, the initial deviation of growth rate for each tree from the predicted rate was calculated and added to the models as a third variable. This raised the coefficient of determination up to 0.50–0.74. These findings have practical significance for forest plantation management, particularly for controlling the growth of standing trees via thinning, to produce high-quality timber in the future.     

Effects of light and microsite conditions on tree size of 6-year-old Cryptomeria japonica planted in a group selection opening

We examined the extent to which direct and indirect measures of light and microsite conditions could explain variation in tree height and diameter at the base of 6-year-old Cryptomeria japonica trees planted in a group selection opening of about 0.32 ha on a steep slope at Shiiba, Miyazaki Prefecture, southern Japan. We first used the gap light index (GLI) and soil thickness (ST) as directly measured indices. For an indirect measure of light, we used a between-cohort competition index (BCI) estimated from the position and total height of residual trees. For indirect measures of microsite, we examined topographic indices (slope, plan and profile curvature, average slope gradient, and relative elevation) derived from digital elevation models (DEMs) with different resolutions ranging from 2 to 10 m. The multiple linear regression using GLI and ST explained about 45% of variation in tree size, while simple regression using only GLI explained about 35%. The contribution of ST was about half of GLI. The multiple regressions using BCI and the topographic indices did not explain any more variation than using BCI alone (R ² of about 0.26). We conclude that microsite conditions with shallower soil and steeper slope have negative effects on tree growth in group selection openings, although the relative importance is smaller than light conditions. More comprehensive studies considering several openings with more heterogeneous topography including different species are needed to generalize our growth prediction using the indirect measures, which are useful for practical forest management.     

Effects of contact with wood on blood pressure and subjective evaluation

This study examined the effects of contact with wood on the living human body using a physiological index and subjective evaluation. Consecutive blood pressure measurements were used as the physiological index, and sensory evaluation using the semantic differential (SD) method was used for subjective evaluation. Consideration was also given to cases in which materials were cooled and heated as well as kept at room temperature, to eliminate the effects of heat flux due to differences in thermal conductivity between wood and other materials. It was found that contact with wood produced coarse/natural sensations, with no associated increase in systolic blood pressure. Contact with cold wood created subjectively dangerous/uncomfortable but still coarse/natural sensations, also with no associated increase in blood pressure; therefore, there was no correspondence between subjective evaluation and physiological responses. Contact with aluminum kept at room temperature and cold acrylic plastic created flat/artificial and dangerous/uncomfortable sensations, with an associated significant increase in blood pressure; thus, there was a close correlation between subjective evaluation and physiological responses. It was therefore concluded that contact with wood, unlike artificial materials such as aluminum, induces no physiological stress even when kept at room temperature or cooled. Part of this report was presented at the 48th Annual Meeting of the Japan Wood Research Society in Shizuoka, April 1998     

Novel plasmodesmata association of dehydrin-like proteins in cold- acclimated Red-osier dogwood (Cornus sericea)

Dehydrins are proteins associated with conditions affecting the water status of plant cells, such as drought, salinity, freezing and seed maturation. Although the function of dehydrins remains unknown, it is hypothesized that they stabilize membranes and macromolecules during cellular dehydration. Red-osier dogwood (Cornus sericea L.), an extremely freeze-tolerant woody plant, accumulates dehydrin-like proteins during cold acclimation and the presence of these proteins is correlated with increased freeze tolerance (Karlson 2001, Sarnighausen et al. 2002, Karlson et al. 2003). Our objective was to determine the location of dehydrins in cold-acclimated C. sericea stems in an effort to provide insight into their potential role in the freeze tolerance of this extremely cold hardy species. Abundant labeling was observed in the nucleus and cytoplasm of cold-acclimated C. sericea stem cells. In addition, labeling was observed in association with plasmodesmata of cold-acclimated vascular cambium cells. The unique association of dehydrin-like proteins with plasmodesmata has not been reported previously.     

Influences of indigenous phototrophs on methane emissions from a straw-amended paddy soil

A pot experiment was conducted to investigate the influences of indigenous phototrophs on methane (CH₄) emissions from a paddy soil where rice straw was incorporated or was surface-applied. During the cultivation, half of the pots were covered with aluminum foil, except for the minimum space for rice plants, to prevent ambient light reaching the floodwater or the soil surface. Growth of oxygen-producing phototrophs was hardly observed in the unilluminated plots, whereas intensive growth of algae, duckweed and hydrophytes was found in the illuminated ones. Plant growth was not affected by the different treatments. Seasonal changes in CH₄ emission determined by a closed chamber method indicated that illumination had no or only minor effects on CH₄ emissions when rice straw was incorporated or was not applied, but significantly reduced CH₄ emissions when rice straw was surface-applied. Methanogenesis occurring in the soil-floodwater interface was further investigated in two lab-scale model experiments measuring methanogenic activity. As a result, more activated methanogenesis was found in the surface-applied rice straw and the soil around the straw compared with the soil incubated without rice straw. The magnitude of the methanogenic activity in the rice straw incubated under illuminated conditions was significantly lower than that incubated in the dark. Consequently, this study demonstrates that methanogenesis in paddy soil occurs even in the soil-floodwater interface if plant residues like rice straw exist, and such methanogenesis is likely to be suppressed by growth of indigenous phototrophs under illumination.