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• Influence of thinning on understory flux components was assessed comprehensively. • Twelve-year long-term monitoring data were used for the assessment. • Thinning increased understory light intensity, soil temperature, and soil moisture. • Increased understory respiration was offset by increased photosynthesis. • Net understory CO 2 exchange was relatively robust compared with each flux component. Thinning is a necessary procedure for the sustainable management of plantation forests. Thinning has a remarkable influence on forest carbon balance; however, there are limited studies showing the integrated assessment of the effects of thinning on several understory carbon flux components using long-term monitoring data. We measured understory flux components using automated chambers continuously over 12 years to understand the effects of forest thinning conducted in May 2014 and March 2015 and to elucidate the effect of short-term climate change on understory carbon balance in a Japanese larch (Larix kaempferi Sarg.) forest in central Japan. Although thinning (39% decrease in tree stems) increased the mean annual soil moisture by 16.5% and growing season soil temperature by 2.4%, large inter-annual variations in precipitation and soil temperature largely masked the effects of thinning on both soil respiration (R s) and soil heterotrophic respiration (R h). Annual mean soil temperature was positively related to all annual efflux components. Thinning also increased the understory photosynthetic photon flux density (PPFD u) by 63.1% during the growing season (May to October). In post-thinning years, the average three-year understory photosynthesis (GPP u), understory plant respiration (R p), and total understory respiration (R u) increased significantly by 59.5%, 99.7%, and 26.9%, respectively. The net understory CO 2 exchange (NUE = R u − GPP u) changed significantly only in 2015 (13.8%). A marginally significant change in NUE based on the three-year average in post-thinning years was also detected (14.4%). Our results indicated each flux component (especially GPP u , R p , and R u) changed dramatically after thinning. In contrast, the NUE of this forest was relatively more robust than other enhanced understory flux components. However, the marginally significant increase of NUE (3-year average in post-thinning years) implied a slight increase in NUE after thinning. [ABSTRACT FROM AUTHOR]

Methane (CH 4 ) fluxes were continuously measured in a temperate forest soil using six dynamic closed chambers with a laser-based analyzer. CH 4 uptake increased with an increase in soil temperature and a decrease in volumetric water content, where multiple linear regressions using the two variables explained approximately 80% of the seasonal variations. Based on the measurements, our forest acted as an annual CH 4 sink with a spatial variation of 25%. The calculated annual CH 4 sink significantly decreased by increasing the chamber deployment period: 8–13 mg CH 4 m −2 yr −1 min −1 . The annual CH 4 sink was significantly different using different calculation methods for the initial slope: 898 ± 11 mg CH 4 m −2 yr −1 using a linear regression, 924 ± 8 mg CH 4 m −2 yr −1 using a quadratic regression, and 975 ± 10 mg CH 4 m −2 yr −1 using an exponential model. These results indicate that underestimations due to disturbing the CH 4 gradient between chamber headspaces and soils were significant despite of the short deployment periods of 4–10 min. Chamber-based fluxes were consistent with canopy-scale CH 4 fluxes by the micrometeorological hyperbolic relaxed eddy accumulation method: sink of 731 ± 38 to 888 ± 87 mg CH 4 m −2 yr −1 . Continuous dynamic closed chambers with laser-based analyzers are a powerful tool to understand CH 4 fluxes in temperate forest soils, as long as a range of uncertainties are carefully evaluated. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured CH4 flux at a forest canopy by a HREA method with laser-based analyzer. [•] The observed annual methane sink was 673–868mg CH4 m−2 yr−1. [•] The precision of a HREA method in the CH4 fluxes was better than that of EC method. [Copyright &y& Elsevier]

To understand climate change’s effect on understory CO 2 flux components, we established automated chambers in a 56-year-old Japanese larch ( Larix kaempferi Sarg.) forest in central Japan for long-term continuous measurements. Between 2006 and 2013, annual CO 2 fluxes ranged from 7.0 to 8.4 tC ha −1 yr −1 for soil respiration ( R s ), 5.7–6.8 tC ha −1 yr −1 for heterotrophic respiration ( R h ), 9.3–10.7 tC ha −1 yr −1 for total understory respiration ( R u ), 2.6–3.5 tC ha −1 yr −1 for understory gross primary production (GPP u ), and 6.1–7.6 tC ha −1 yr −1 for net understory CO 2 exchange (NUE). Mean annual soil temperature (MAT s ), especially in spring, was positively related to annual R s , R h , R u , and NUE. Based on the inter-annual relationship between MAT s and annual understory CO 2 effluxes, a 1 °C MAT s increase was estimated to increase annual effluxes by 25.1% for R s and R h , 14.4% for R u , and 23.9% for NUE. The growing season CO 2 flux components were weakly associated with soil moisture. However, during a short dry period in the summer of 2013, we observed a strong relationship between soil moisture and understory R s , R h , and R u . GPP u was primarily controlled by the understory light intensity; GPP u during growing season increased where the canopy was disturbed by typhoons in the early growing seasons in 2007 (+9.8%) and 2012 (+24.4%) as well as during the 2013 growing season (+12.2%) due to a short drought. Understory CO 2 effluxes in this larch forest will likely increase under global warming. [ABSTRACT FROM AUTHOR]

• CH 4 fluxes were observed by chambers in an upland forest soil over seven years. • Modules for CH 4 uptake were calibrated by the observed data with a Bayesian method. • After calibrating two parameters, the modules reproduced the observed fluxes well. • Future CH 4 fluxes were predicted to increase with rising CH 4 concentrations. • The modules contained high uncertainty levels in future predictions even after the calibration. Upland soils are thought to be a sink of CH 4 , the second most important anthropogenic greenhouse gas, owing to oxidation by methanotrophs. To better understand CH 4 fluxes in upland forests, we quasi-continuously measured CH 4 fluxes using an automated closed chamber system over seven years on a larch plantation in a volcanic soil in Japan. We hypothesized that the long-term data sufficiently can calibrate modules for CH 4 fluxes, and aimed to predict future pathways of CH 4 uptake and their uncertainties in the forest. Based on the observations, a thinning of the overstory only marginally influenced the CH 4 fluxes measured by the chambers. Using the data with a Bayesian method, we calibrated four modules for CH 4 fluxes in forest soils, which were embedded in the process-based ecosystem model VISIT. The modules well reproduced the observed seasonality, annual budgets, and interannual variability in the CH 4 fluxes after calibrating the following parameters: the diffusion coefficient or base CH 4 oxidation rate constant and temperature sensitivity. The CH 4 fluxes were predicted to increase in the future under the RCP8.5 scenario but to decrease under the RCP 2.6 scenario. The contrasting trajectory was caused by rising and decreasing CH 4 concentrations under the RCP 8.5 and 2.6 scenarios, respectively. Furthermore, the magnitudes of the future changes in the fluxes differed in each module because the responses to the changes in the CH 4 concentrations were inconsistent among the modules. The observed CH 4 fluxes increased with increasing atmospheric CH 4 concentration (4.95 mg CH 4 m−2 d−1 ppm−1), which was greater in magnitude than those in the modules. Considering the uncertainties in the modules and potential confounding effects in the observations, we conclude that further understanding the responses of CH 4 uptake to rising CH 4 concentrations is required. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports 3-year measurements (2001–2003) of the net ecosystem CO2 exchange (NEE) over a northern Japan larch plantation forest, using an eddy covariance technique with both open- and closed-path systems. The study evaluates interannual variations in the seasonal patterns of NEE, the annual NEE, clarifying the factors controlling the carbon balance. NEE for both open- and closed-path systems look equivalent from the half-hourly mean values; however, there is a small systematic bias in the annual cumulative totals. In this study, we used closed-path data because open-path data during winter are doubtful and the annual NEE from closed-path data was closer to the biometric NEP than that from open-path data. The 3-year averages of annual NEE, gross primary production (GPP), and ecosystem respiration (RE) were −212±43 (standard deviation), −1673±59, and 1462±42gCm−2 y−1, respectively. The larch plantation forest absorbed large amounts of CO2 during just 1 month, June. During that period, photosynthetic photon flux density (PPFD) was large while the temperature was not high. These meteorological conditions were suitable for CO2 absorption before the leaf area index (LAI) reached its peak. Maximum GPP at light saturation (P max) was also large. During the 3-year measurement period, PPFD in summer, and temperatures in spring and summer engendered remarkable interannual differences of GPP, RE, and NEE. In spring, snowmelt and larch foliation occurred about 2 weeks earlier in 2002 than in either 2001 or 2003 because of higher temperatures; consequently, the ecosystem began to photosynthesize earlier. In July, NEE was more negative in 2003 than in other years. The GPP became larger because of higher PPFD, larger P max; while the RE became smaller because of lower temperatures. Compared with similar forests, the amounts of GPP and RE measured here were large, but NEE was similar. The reason is that the photosynthetic capacity of larch is naturally large: the ample PPFD, and the lack of environmental stresses from dry air or soil, consequently allows high photosynthesis rates to be maintained. Moreover, it can be inferred that RE values are enhanced by the high photosynthetic activity of larch forest during the growing season. [Copyright &y& Elsevier]

• Variations in methane emissions from a shallow mid-latitude lake were examined. • This lake had areas with steady bubble methane emissions. • The steady bubble emission was seasonally controlled by the hydrostatic pressure. • Methane emissions from the other area was seasonally controlled by temperature. Temporal and spatial variations in methane (CH 4) emissions from the littoral zone of a shallow mid-latitude lake, Lake Suwa, were examined using the eddy covariance technique. The observation data were supplemented with dissolved CH 4 measurement and incubation experiments of lake sediment and water. This lake had areas with steady bubble CH 4 emissions, shaping the spatial variation in CH 4 flux with strong spot emissions. In the other areas, CH 4 was emitted via diffusion and episodic ebullition. CH 4 emissions from this area had a clear seasonal variation, reflecting temperature variations, with a maximum monthly mean emission of 0.39 µ mol m − 2 s − 1 in August. The higher emission in summer was due to higher CH 4 production in the sediment and the resulting higher dissolved CH 4 concentration in the surface water. The steady bubble CH 4 emission was seasonally controlled by the total hydrostatic pressure, with higher emission under lower pressure, suggesting regulation of the amount of bubbles emitted from the lake bottom by pressure. Isotope analysis revealed that this CH 4 was produced biologically. This natural gas seepage was estimated to emit 1.9 Mg of CH 4 annually. Compared with other eddy covariance studies over inland waters, CH 4 emissions from Lake Suwa may be large for the latitude. This may be related to eutrophication, which enhances CH 4 production. [ABSTRACT FROM AUTHOR]