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Forests play an important role in mitigating climate change. It can not only provide carbon sequestration in standing forests and long-life forest products, but can also reduce carbon release by bioenergy’s substitution of fossil fuel. Therefore, a comprehensive impact from forest carbon on landowners’ forest management decisions should be analyzed when considering those uncertainties in carbon life cycle. The first part of the dissertation is a meta-analysis review, in which important factors that can influence the estimation of harvesting rotations under carbon sequestration are summarized and analyzed. It concludes that some issues as natural disturbances and forest bioenergy deserve more attentions, which are addressed in the following two chapters. The second part adopts a revised Faustmann model to assess the relation between wildfire risk and prescribed fire under four assumed carbon policy scenarios. It arrives at the conclusion that penalty on carbon release in prescribed fire may reduce carbon sequestration in standing forests and make forest landowners to take the risk of loss in wildfire. Thus, a carbon policy with such a regulation should be adopted with caution. The third part investigates the probable influence brought by wood-based biofuel of stochastic prices with a Monte Carlo method. The results demonstrate that the assumption of double stochastic prices leads to earlier harvesting when comparing to constant price scenario or stochastic price assumption of only timber. The stochasticity of energy price may benefit landowners but also introduce uncertainties into their revenue. It also reduces sequestered carbon in standing forests and long-life forest products, which should be paid more attention when a general point of view on forest carbon is the concern. This project is informative for landowners who are facing new opportunities and challenges in forest management and is also helpful for carbon policy makers when dealing with forest carbon dilemmas of prescribed fire and bioenergy.

The boreal forest is one of the worlds largest forest biomes and comprises a major portion of the terrestrial carbon (C) sink. Quantifying the net C change in forest ecosystems is an important step in understanding and modeling the global C cycle. The goals of this project were: to estimate and compare the total change in ecosystem C over a 10-year period in two boreal forest stands using biometric and eddy-covariance approaches, and to evaluate the year-to-year changes in C uptake. This study utilized 10 years of eddy-covariance data and ecosys model data from the Old Aspen (OA) and Old Jack Pine (OJP) sites in central Saskatchewan, part of the Boreal Ecosystem Research and Monitoring Sites (BERMS). According to the eddy-covariance and C stock approaches, between 1994 and 2004 the net change in C storage at OA was 15.6 ± 4.0 and 18.2 ± 8.0 Mg C ha-1, respectively. At OJP, the 10-year net change in C storage from eddy-covariance was 5.8 ± 2.0 Mg C ha-1 in comparison to 6.9 ± 1.6 Mg C ha-1 from the carbon stock approach. While both sites were sinks of C between 1994 and 2004, the greatest increase in C occurred in different components - the forest floor at OA (14.6 Mg C ha-1) and in the living vegetation at OJP (8.0 Mg C ha-1). In 2004, total ecosystem C content was greater at OA (180.6 Mg C ha-1) than OJP (78.9 Mg C ha-1), with 50% (OA) and 39% (OJP) of the C in the detritus and mineral soil pools. During the 10-year period of eddy-covariance measurements, there was a positive correlation between both annual and growing season gross ecosystem photosynthesis (GEP) and live stem C biomass increment at OA, whereas no significant relationships were found at OJP. Stem C increment accounted for 30% of total net primary productivity (NPP) at both sites, and NPP/GEP ratios were 0.36 and 0.32 at OA and OJP, respectively. Overall, this study found good agreement between eddy-covariance and biometric estimates of ecosystem C change at OA and OJP between 1994 and 2004. Over that period at OA, eddy-covariance estimates of photosynthesis captured the inter-annual variability in C uptake based on the growth of tree rings.

The boreal forest is one of the worlds largest forest biomes and comprises a major portion of the terrestrial carbon (C) sink. Quantifying the net C change in forest ecosystems is an important step in understanding and modeling the global C cycle. The goals of this project were: to estimate and compare the total change in ecosystem C over a 10-year period in two boreal forest stands using biometric and eddy-covariance approaches, and to evaluate the year-to-year changes in C uptake. This study utilized 10 years of eddy-covariance data and ecosys model data from the Old Aspen (OA) and Old Jack Pine (OJP) sites in central Saskatchewan, part of the Boreal Ecosystem Research and Monitoring Sites (BERMS). According to the eddy-covariance and C stock approaches, between 1994 and 2004 the net change in C storage at OA was 15.6 ± 4.0 and 18.2 ± 8.0 Mg C ha-1, respectively. At OJP, the 10-year net change in C storage from eddy-covariance was 5.8 ± 2.0 Mg C ha-1 in comparison to 6.9 ± 1.6 Mg C ha-1 from the carbon stock approach. While both sites were sinks of C between 1994 and 2004, the greatest increase in C occurred in different components - the forest floor at OA (14.6 Mg C ha-1) and in the living vegetation at OJP (8.0 Mg C ha-1). In 2004, total ecosystem C content was greater at OA (180.6 Mg C ha-1) than OJP (78.9 Mg C ha-1), with 50% (OA) and 39% (OJP) of the C in the detritus and mineral soil pools. During the 10-year period of eddy-covariance measurements, there was a positive correlation between both annual and growing season gross ecosystem photosynthesis (GEP) and live stem C biomass increment at OA, whereas no significant relationships were found at OJP. Stem C increment accounted for 30% of total net primary productivity (NPP) at both sites, and NPP/GEP ratios were 0.36 and 0.32 at OA and OJP, respectively. Overall, this study found good agreement between eddy-covariance and biometric estimates of ecosystem C change at OA and OJP between 1994 and 2004. Over that period at OA, eddy-covariance estimates of photosynthesis captured the inter-annual variability in C uptake based on the growth of tree rings.

Since the 1980s, hemlock-dominated forests (Tsuga canadensis) of central New England have been increasingly infested by the invasive pest hemlock woolly adelgid (HWA, Adelges tsugae), predominantly resulting in its replacement by black birch-dominated forests (Betula lenta). To date there has been no long-term empirical analysis of HWA effects on forest carbon (C) cycling due to forest transition from hemlock to black birch. To address this question, I measured the C pools in five stand types at varying ages and stages of HWA infestation in Massachusetts and Connecticut. I also measured C fluxes in aboveground net primary production (ANPP) and soil respiration, and studied the drivers of these fluxes viz. litter production, rates of foliar decomposition, soil exoenzyme activity, temperature sensitivity of soil respiration and nitrogen (N) cycling. The mass of C stored in recovering forests was resilient to HWA infestation but the location of these stocks varied among stand types. There was a transition of C from live biomass in healthy, unaffected secondary hemlock forests to coarse woody debris (CWD) in recently girdled forests intended to simulate the effect of HWA on hemlock loss. Twenty years post-HWA infestation, however, ANPP was very high and there was a large increase in biomass-C pools in aggrading black stand types. C pools in mature, secondary black birch stand types ~135 years since pastureland abandonment were as large as those in primary hemlock stand types ~235 years of age, suggesting recovery of C storage within one century of HWA infestation. Soil respiration rates were positively correlated with inputs of hardwood leaf litter, fine root biomass and exoenzyme activity. Stand-type variations in ANPP were positively correlated with annual N requirements and N uptake from the soil. Nitrogen-use efficiency was highest in the girdled and post-HWA infestation stand types where ANPP was dominated by wood production which has a wide C:N ratio. Similar trends were found in soil respiration, but not to the same degree as that of ANPP. Collectively, my results indicate that southern New England forests C storage is highly resilient to the HWA-induced losses of hemlock, suggesting that these ecosystems will continue to be sinks for atmospheric carbon dioxide.

Northern peatlands are an important carbon store, with carbon dynamics and hydrology intrinsically linked. The riparian zone is the interface between the terrestrial and aquatic systems, situated adjacent to the stream and characterised by periodic flooding, near surface water tables and unique soil and plant species composition. Due to its unique biogeochemical environment, the riparian zone has the potential to modify significantly the production, mobilisation and transport of carbon via the land-atmosphere and aquatic pathways. Two contrasting headwater catchments, an ombrotrophic peatland (Auchencorth Moss, SE Scotland) and a forested, till dominated catchment (Västrabäcken, N Sweden), were investigated. In each carbon concentrations in soil and stream water and hydrological parameters were measured in transects connecting the wider catchment, riparian zone and stream. The overarching aim was to investigate the role of the riparian zone on the hydrological and bio-geochemical functioning of peatland and forested catchments, focusing on carbon export via the aquatic pathway. Specific objectives were to: a) examine the importance of soils, water table and vegetation composition on riparian biogeochemical cycling, b) investigate riparian-stream hydrological connectivity and the transport of carbon across the soil-water interface and c) assess riparian processes in relation to the net ecosystem carbon balance (NECB) across northern latitude ecosystems. Porewater total carbon (TC) concentrations (sum of dissolved organic and inorganic carbon (DOC, DIC), CO2 and CH4) were on average higher in Auchencorth Moss (78.8-140 mg C L-1) than the Västrabäcken (27.7-63.2 mg C L-1) catchment. In both catchments, higher TC concentrations were observed in the riparian zone compared to the wider catchment. The dominant control for differentiating between catchment and riparian biogeochemical processes was the higher average riparian water table with each carbon species displaying a positive relationship with water table height. A range of other factors, including soil temperature and the carbon content of catchment and riparian soils, also contributed to the complexity of riparian carbon biogeochemical cycles. Catchment specific phenomena, including the presence of aerenchymous vegetation and stream sediment deposition onto the riparian zone, modified riparian carbon dynamics in the Auchencorth Moss catchment. Isotopically, porewater DOC, CO2 and CH4 had a 14C content >100 %modern, indicating that the modern plant derived DOC is being transported down the soil profile, providing the source for CO2 and CH4 production at depth. In both catchments the riparian zone represented an important and dynamic source of carbon to stream waters. Total annual CO2 export from the riparian zone of the Västrabäcken catchment to the stream channel over the hydrological year was 2.7 g CO2-C m2 yr-1 with export predominantly from between 40 and 55 cm depth within the soil. Two monthly peaks in CO2 export occurred over the hydrological year related to either storm events or the spring snow melt period which accounted for 19 % of annual export, highlighting the temporal variability in soil-stream linkages, especially during high flow periods. In the generally wetter peatland catchment, riparian-stream linkages were driven by antecedent conditions and variation in riparian water table, with changes in water input, rather than changes in CO2 source concentrations, controlling stream water composition. The negative CO2 concentration-discharge relationship in the stream suggested that event water dominated, with small but important inputs from high concentration soil water during individual events. The importance of event water in transporting carbon was confirmed through the isotope result. CO2, CH4 and DOC exported via the aquatic pathway predominantly contained modern, plant derived carbon from the near surface soil horizons but with a small contribution (5-28 %) from deeper geological sources leading to aged evasion CH4 (310-537 years BP) and CO2 (36 years BP to modern). In both catchments the riparian zone was more important, relative to the wider catchment, in controlling the export of carbon via the aquatic pathway. At Auchencorth Moss, the riparian zone, plus an area of the catchment extending ~20 m from the stream, were hotspots for land-atmosphere fluxes of CH4, with mean flux of 1.08-7.70 mg m2 hr-1 in comparison to the catchment overall (0.05 mg m2 hr-1). In both catchments, combining detailed catchment hydrological models with high temporal resolution carbon concentration measurements, especially in riparian zone soils, has the potential to improve estimates of downstream and evaded carbon export in headwater catchments. Riparian zones should therefore be included more in studies investigating hydrological and biogeochemical processes in northern latitude headwater catchments. The processes within riparian zones suggest that despite the relatively small area that riparian zones represent, in relation to the wider catchment, they may play an important role in the NECB of peatland and forested catchments under future management and climate change scenarios.

This study examined the annual C balance and its shifting trend in Canada’s managed forests from 1991 to 2006 using the Integrated Terrestrial Ecosystem C-budget (InTEC) model. During this period, Canada’s managed forests remained a moderate C sink of 58 Mt C yr¬¬¬-1 on average, but displayed an apparent trend of shifting towards a C source. The combined risk of climate change and increased disturbances are weakening the C sink in Canada’s managed forests. This study also compared the results from InTEC with those from CBM-CFS (Carbon Budget Model of the Canadian Forest Sector) at both national and regional levels. InTEC shows larger inter-annual variability and regional difference than CBM-CFS due to its incorporation of both disturbance and non-disturbance factors. In comparison, CBM-CFS3 has likely underestimated both the true C loss and the C sink potential of Canada’s managed forests, given that it does not account for the non-disturbance factors.

This study examined the annual C balance and its shifting trend in Canada’s managed forests from 1991 to 2006 using the Integrated Terrestrial Ecosystem C-budget (InTEC) model. During this period, Canada’s managed forests remained a moderate C sink of 58 Mt C yr¬¬¬-1 on average, but displayed an apparent trend of shifting towards a C source. The combined risk of climate change and increased disturbances are weakening the C sink in Canada’s managed forests. This study also compared the results from InTEC with those from CBM-CFS (Carbon Budget Model of the Canadian Forest Sector) at both national and regional levels. InTEC shows larger inter-annual variability and regional difference than CBM-CFS due to its incorporation of both disturbance and non-disturbance factors. In comparison, CBM-CFS3 has likely underestimated both the true C loss and the C sink potential of Canada’s managed forests, given that it does not account for the non-disturbance factors.

京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第22022号 / 地環博第186号 / 新制||地||96(附属図書館) / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)准教授 岡田 直紀, 教授 舟川 晋也, 准教授 真常 仁志 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DGAM

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