To estimate the aboveground biomass of tropical secondary forests dominated by pioneer species, allometric equations to relate diameter at breast height with the dry mass of the aboveground organs of several pioneer species were developed. The aboveground biomass of secondary forests was estimated using four methods based on the allometric equations. Biomass estimated with an allometric equation for all species combined was equivalent to that estimated with species-specific allometric equations. However, the estimated biomass based on a general-purpose allometric equation was substantially higher than that using other allometric equations. The allometric equation for all species combined is suitable for estimating the biomass of a secondary forest from the view points of accuracy and labor.
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.
Forest soil is a huge reserve of carbon in the biosphere. Therefore to understand the carbon cycle in forest ecosystems, it is important to determine the dynamics of soil CO 2 efflux. This study was conducted to describe temporal variations in soil CO 2 efflux and identify the environmental factors that affect it. We measured soil CO 2 efflux continuously in a beech secondary forest in the Appi Highlands in Iwate Prefecture for two years (except when there was snow cover) using four dynamic closed chambers that automatically open after taking measurements. Temporal changes in soil temperature and volumetric soil water content were also measured at a depth of 5 cm. The soil CO 2 efflux ranged from 14 mg CO 2 m -2 h -1 to 2,329 mg CO 2 m -2 h -1 , the peak occurring at the beginning of August. The relationship between soil temperature and soil CO 2 efflux was well represented by an exponential function. Most of temporal variation in soil CO 2 efflux was explained by soil temperature rather than volumetric soil water content. The Q 10 values were 3.7 ± 0.8 and estimated annual carbon emissions were 837 ± 210 g C m -2 year -1 . These results provide a foundation for further development of models for prediction of soil CO 2 efflux driven by environmental factors.
For a successful natural regeneration of Japanese white birch (Betula platyphylla var. japonica), competitive vegetation should be managed. Here, we clarified how soil water condition modifies the competitiveness of Japanese white birch against perennial weeds, Eupatorium species, based on an ecophysiological approach combining a glasshouse experiment and a field survey. We investigated photosynthetic and growth responses to various water regimes from water deficit to waterlogging (two times-a-week irrigation, three times-a-week irrigation, half waterlogging, and full waterlogging) in pot-grown seedlings of Japanese white birch and the competitive weed Eupatorium makinoi. The ratio of seedling height of Japanese white birch to seedling height of E. makinoi showed a decreasing trend from two times-a-week irrigation to full waterlogging, which suggests a lower competitiveness for light resource in Japanese white birch with increasing soil wetness. The maximum rate of Rubisco carboxylation (Vc,max) based on unit N was lower in waterlogging treatments than in two times- and three times-a-week irrigation in Japanese white birch, whereas E. makinoi showed the opposite response. This suggests that N partitioning into Rubisco and/or Rubisco activation might be suppressed in Japanese white birch but enhanced in E. makinoi under waterlogging. The maximum photochemical efficiency of photosystem II (Fv/Fm) was also lower in seedlings of Japanese white birch grown under waterlogging treatments. We further conducted a field survey on the relationship between Fv/Fm and topographic wetness index (TWI) in seedlings of Japanese white birch and E. glehnii (closely related to E. makinoi) naturally grown in a study site 5 years after canopy tree cutting. Lower Fv/Fm was observed in seedlings of Japanese white birch with increasing TWI, whereas no significant trend was observed in E. glehnii, in agreement with the glasshouse experiment. Thus, keeping soils not always humid might be favorable to photosynthetic performance and growth competitive ability of Japanese white birch against Eupatorium species.
CO 2 1 2 2 3 CO 2 90 386 390, 2008 CO 2 35 m 35 m 49 CO 2 CO 2 15.8 26.7 1 CO 2 CO 2 CO 2
To identify the soil carbon stock change from cropland to forest land in Japan, we compared the soil carbon stock of a cropland and that of an adjacent forest land at 23 different sites. With regard to a 0-30 cm depth basis, the soil carbon stock in the cropland was greater than that in the forest land; however, it was less than that in the forest land when an equivalent mass basis was used. In less than an elapsed time of 20 years after a land-use change, the soil carbon stock after afforestation was less than that in the adjacent cropland at the same sites. However, after an elapsed time of 20 years, the soil carbon stock in the afforested site exceeded that in the adjacent cropland at the same sites. The ratio of the soil carbon stock in forest land to that in the cropland was 1.10 on average, which is comparable with the previous mass-corrected paired-sampling studies. The ratio in the conifer-planted forest was significantly greater than that in the hardwood re-generated forest. Some of the previous reviews, including those of the non-mass-corrected data, were possibly biased, and more studies using the paired-sampling method with equivalent mass basis need to provide more general ratios in the future.
5 (2018) Recovery of Soil Penetration Resistance on Compacted Skid Trails after Forest Thinning in Central Hokkaido. J Jpn For Soc 100: 110⊖115 Vehicular traffic on skid trails after forest thinning causes compaction, leading to increased soil penetration resistance. In this study, we investigated the recovery of soil penetration resistance after thinning in a planted Todo fir forest. The soil penetration resistance profile of upper soil (to a depth of 0.6 m) was measured on a skid trail before thinning (2008) , immediately after thinning (2008) , and 5 and 6 years after thinning (2013 and 2014, respectively). The penetration resistance profile revealed that a hard soil layer formed down to a depth of 0.2 m immediately after thinning; however, soil penetration resistance and the soil compaction index decreased 6 years after thinning. Thus, our results indicate that compaction effects on skid trails disappear 5 or 6 years after the event. A "soil compaction index" (SCI) was created to evaluate the degree of soil compaction. SCI can indicate the degree of soil compaction as one numerical value.
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