Simulating age-related changes in carbon storage and allocation in a Chinese fir plantation growing in southern China using the 3-PG model

Chinese fir [(Cunninghamia lanceolata (Lamb.) Hook (Taxodiaceae)] plantations are helping to meet China's increasing demands for timber, while, at the same time, sequestering carbon (C) above and belowground. The latter function is important as a means of slowing the rate that CO₂ is increasing in the atmosphere. Available data are limited, however, and even if extensive, would necessitate consideration of future changes in climatic conditions and management practices. To evaluate the contribution of Chinese fir plantations under a range of changing conditions a dynamic model is required. In this paper, we report successful outcome in parameterizing a process-based model (3-PG) and validating its predictions with recent and long-term field measurements acquired from different ages of Chinese fir plantations at the Huitong National Forest Ecosystem Research Station. Once parameterized, the model performed well when simulating leaf area index (LAI), net primary productivity (NPP), biomass of stems (W_S), foliage (W_F) and roots (W_R), litterfall, and shifts in allocation over a period of time. Although the model does not specifically include heterotrophic respiration, we made some attempts to estimate changes in root C storage and decomposition rates in the litterfall pool as well as in the total soil respiration. Total C stored in biomass increased rapidly, peaking at age 21 years in unthinned stands. The predicted averaged above and belowground NNP (13.81 t ha⁻¹ a⁻¹) of the Chinese fir plantations between the modeling period (from 4 to 21-year-old) is much higher than that of Chinese forests (4.8–6.22 t ha⁻¹ a⁻¹), indicating that Chinese fir is a suitable tree species to grow for timber while processing the potential to act as a C sequestration sink. Taking into account that maximum LAI occurs at the age of 15 years, intermediate thinning and nutrient supplements should, according to model predictions, further increase growth and C storage in Chinese fir stands. Predicted future increases (approximately 0–2 °C) in temperature due to global warming may increase plantation growth and reduce the time required to complete a rotation, but further increases (approximately 2–6 °C) may reduce the growth rate and prolong the rotational age.     

The impact of nitrogen deposition on carbon sequestration by European forests and heathlands

In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) ¹⁵N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40 kg C/kg N. For heathlands, a range of 5–15 kg C/kg N has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kg N addition in soils is larger than for above-ground biomass and varies on average between 5 and 35 kg C/kg N for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75 kg C/kg N deposition for forest and heathlands, with a most common range of 20–40 kg C/kg N. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses.     

Risks to forest carbon offset projects in a changing climate

When included as part of a larger greenhouse gas (GHG) emissions reduction program, forest offsets may provide low-cost opportunities for GHG mitigation. One barrier to including forest offsets in climate policy is the risk of reversal, the intentional or unintentional release of carbon back to the atmosphere due to storms, fire, pests, land use decisions, and many other factors. To address this shortcoming, a variety of different strategies have emerged to minimize either the risk or the financial and environmental implications of reversal. These strategies range from management decisions made at the individual stand level to buffers and set-asides that function across entire trading programs. For such strategies to work, the actual risk and magnitude of potential reversals need to be clearly understood. In this paper we examine three factors that are likely to influence reversal risk: natural disturbances (such as storms, fire, and insect outbreaks), climate change, and landowner behavior. Although increases in atmospheric CO₂ and to a lesser extent warming will likely bring benefits to some forest ecosystems, temperature stress may result in others. Furthermore, optimism based on experimental results of physiology and growth must be tempered with knowledge that future large-scale disturbances and extreme weather events are also likely to increase. At the individual project level, management strategies such as manipulation of forest structure, age, and composition can be used to influence carbon sequestration and reversal risk. Because some management strategies have the potential to maximize risk or carbon objectives at the expense of the other, policymakers should ensure that forest offset policies and programs do not provide the singular incentive to maximize carbon storage. Given the scale and magnitude of potential disturbance events in the future, however, management decisions at the individual project level may be insufficient to adequately address reversal risk; other, non-silvicultural strategies and policy mechanisms may be necessary. We conclude with a brief review of policy mechanisms that have been developed or proposed to help manage or mitigate reversal risk at both individual project and policy-wide scales.     

Below- and above-ground biomass and net primary production in a paleotropical natural forest (Sulawesi,Indonesia) as compared to neotropical forests

Data on the biomass and productivity of southeast Asian tropical forests are rare, making it difficult to evaluate the role of these forest ecosystems in the global carbon cycle and the effects of increasing deforestation rates in this region. In particular, more precise information on size and dynamics of the root system is needed. In six natural forest stands at pre-montane elevation (c. 1000 m a.s.l.) on Sulawesi (Indonesia), we determined above-ground biomass and the distribution of fine (d < 2 mm) and coarse roots (d > 2 mm), estimated above- and below-ground net production, and compared the results to literature data from other pre-montane paleo- and neotropical forests. The mean total biomass of the stands was 303 Mg ha⁻¹ (or 128 Mg C ha⁻¹), with the largest biomass fraction being recorded for the above-ground components (286 Mg ha⁻¹) and 11.2 and 5.6 Mg ha⁻¹ of coarse and fine root biomass (down to 300 cm in the soil profile), resulting in a remarkably high shoot:root ratio of c. 17. Fine root density in the soil profile showed an exponential decrease with soil depth that was closely related to the concentrations of base cations, soil pH and in particular of total P and N. The above-ground biomass of these stands was found to be much higher than that of pre-montane forests in the Neotropics, on average, but lower compared to other pre-montane forests in the Paleotropics, in particular when compared with dipterocarp forests in Malesia. The total above- and below-ground net primary production was estimated at 15.2 Mg ha⁻¹ yr⁻¹ (or 6.7 Mg C ha⁻¹ yr⁻¹) with 14% of this stand total being invested below-ground and 86% representing above-ground net primary production. Leaf production was found to exceed net primary production of stem wood. The estimated above-ground production was high in relation to the mean calculated for pre-montane forests on a global scale, but it was markedly lower compared to data on dipterocarp forests in South-east Asia. We conclude that the studied forest plots on Sulawesi follow the general trend of higher biomasses and productivity found for paleotropical pre-montane forest compared to neotropical ones. However, biomass stocks and productivity appear to be lower in these Fagaceae-rich forests on Sulawesi than in dipterocarp forests of Malesia.     

油松人工林碳汇功能的研究

对木兰林管局油松人工林19块标准地分林木层、灌木层、草本植物层、枯落物层和土壤层进行了生物现存量的实测与碳储量的研究,结果表明林木层和土壤层的碳储量构成了林分碳储量的主体.分配次序为土壤层＞林木层＞地表枯落物层＞草本层＞根桩＞灌木层,林木层碳储量分配次序为干＞枝＞根＞叶.建立了林木蓄积与生物量、碳储量的回归模型,认为幂函数形式有较好的适用性.以林龄(A)和3株优势木平均高(H)建立了土壤有机碳密度(Soc)拟合方程,可用于具体小班土壤碳密度的估测.木兰林管局油松人工林林分碳密度为76.586 2～284.417 8t/hm2,平均值为143.1 t/hm2,其中林木平均碳密度为30.454 5t/hm2,土壤平均碳密度为110.773 5t/hm2;现有油松人工林碳储量估测结果为983 314.0 t,其中林木碳储量为208 923.0 t,占总碳储量的21.25%,土壤碳储量为760 881.0 t,占总碳储量的77.38%.     

我国竹林碳汇项目可行性分析

介绍了碳汇项目的研究背景和相关概念,分析认为,竹林碳汇项目具有资源广、潜力大、条件成熟等优势;同时,也具有易受自然灾害及林地管理、碳汇计量、碳汇交易困难等不足,对竹林碳汇项目的实施形成了阻碍。进而提出了提高竹林碳汇含量、明确林权、加强科研投入、提高碳汇效益等发展建议。     

Carbon sequestration in Spanish Mediterranean forests under two management alternatives: a modeling approach

Management implications associated with two different silvicultural strategies in two Spanish pine forests (Scots pine stands in northern Spain and Mediterranean Maritime pine stands in Central Spain) were explored. Whole-stand yield, growth models and individual tree equations were used to estimate carbon stock in forests under different silvicultural alternatives and site indexes. Each alternative was evaluated on the basis of the land expectation value (LEV). Results reveal the appropriateness of implementing carbon payments, because it can clearly complement traditional management objectives in economic terms. Longer rotations on the poorest sites result in a positive economic return by introducing carbon output. The proportion of carbon stock in the final harvest relative to total fixed carbon is always higher in long rotation scenarios. However, short rotation systems produce the highest values of carbon MAI regardless of site index. The impact of carbon price is higher on the Maritime pine stands than on Scots pine stands. For both the species, changes in the discount rate have a minor impact on Carbon LEV. Notwithstanding, the proportion of total LEV due to carbon is greater when the discount rate increases.     

城市生态系统土壤碳储量的研究进展

介绍国内外估算城市生态系统土壤碳储量的研究进展,并提出今后发展的方向。     

Assessment of nitrogen losses to the environment with a Nitrogen Trading Tool (NTT)

Nitrogen (N) losses from agriculture often contribute to reduced air, groundwater, and surface water quality. The minimization of these N losses is desirable from an environmental standpoint, and a recent interest in discounted reductions of agricultural N losses that might apply to a project downstream from an agricultural area has resulted in the concept of N credits and associated N trading. To help quantify management-induced reductions in N losses at the farm field level (essential components of a Nitrogen Trading Tool), we defined a Nitrogen Trading Tool difference in reactive N losses (NTT-DNL_reac) as the comparison between a baseline and new management scenarios. We used a newly released Windows XP version of the Nitrogen Losses and Environmental Assessment Package (NLEAP) simulation model with Geographic Information System (GIS) capabilities (NLEAP-GIS) to assess no-till systems from a humid North Atlantic US site, manure management from a Midwestern US site, and irrigated cropland from an arid Western US site. The new NTT-DNL_reac can be used to identify the best scenario that shows the greatest potential to maximize field-level savings in reactive N for environmental conservation and potential N credits to trade. A positive NTT-DNL_reac means that the new N management practice increases the savings in reactive N with potential to trade these savings as N credits. A negative number means that there is no savings in reactive N and no N available to trade. The new NLEAP-GIS can be used to quickly identify the best scenario that shows the greatest potential to maximize field-level savings in reactive N for environmental conservation and earning N credits for trade.     

循环水养鳗系统生物过滤器中微生物群落的代谢特性

为了研究鳗鱼循环水养殖系统不同水处理单元的微生物群落碳代谢特征,实验采用Biolog Eco技术,分析了流化床两个槽和滴流式生物过滤器上、中、下三层的生物膜微生物群落功能多样性。结果显示,流化床两个槽和滴流式生物过滤器中、下层微生物多样性指数（Shannon-Wiener指数、Simpson指数和Pielou指数）无显著差异（P>0.05）,但均显著高于滴流式生物过滤器上层（P<0.05）。平均色度变化（AWCD）与主成分分析（PCA）均证明滴流式生物过滤器上层与其它采样点微生物代谢差异较大。各采样点微生物未对ECO板某一大类碳源表现出偏好,但对衣康酸、D-半乳糖醛酸、L-精氨酸、L-天门冬酰胺、L-丝氨酸、D-甘露醇、D-木糖、N-乙酰-D-葡萄糖氨、吐温40、吐温80、苯乙胺等单一碳源利用较好;而对γ-羟丁酸和α-丁酮酸以及D,L-α-磷酸甘油和1-磷酸葡萄糖利用较差。某些碳源种类如D-葡糖胺酸、α-D-乳糖、2-羟基苯甲酸仅能被部分采样点的微生物利用。本实验利用Biolog EcoPlateTM技术研究中试规模循环水处理单元微生物群落代谢特征,研究结果为生物过滤器的调控提供了一种新的思路即可以通过碳源调节,来促进生物膜微生物群落结构的改变以此提高水处理效率。