长期开垦与放牧对内蒙古典型草原地下碳截存的影响

以围封26 a草地(E26)为对照,研究了内蒙古典型草原区长期开垦与放牧对土壤-植物根系系统碳截存的影响.结果表明,0～40 cm土壤和根系中的C贮量, E26(7 307.59和950.32 g·m-2)≈连续放牧草地(LG)(7834.01和843.43 g·m-2)>开垦35 a耕地(LC)(4537.04和277.35 g·m-2). E26、LG和LC中,0～40 cm土壤贮存的C分别占各自土壤-根系系统C总贮量的88.49%、90.28%和94.24%.长期开垦完全破坏了草地原生的植被-土壤系统,造成严重的土壤风蚀:相对于E26,比中O～10 cm和10～20 cm砂粒含量分别增加了81%和39%,0～40 cm土层中根系生物量减少了71%;长期开垦导致草地土壤及根系碳截存分别降低了37.9%和70.8%.因此,在草原地区,若将长期开垦的耕地恢复为天然草地,土壤和植物根系将会有较大的固碳潜力.放牧对该区土壤有机碳含量及根系生长的影响较小;但长期放牧样地土壤表层容重显著增加,预示目前放牧压力已达到或接近草地的承载阈值,应及时减小放牧压力以避免草地的进一步退化.     

Model Computations on Sequestration of Carbon in Managed Forests and Wood Products under Changing Climatic Conditions in Finland

The aim of this study was to assess the effects of forest management on carbon sequestration in forests and wood products by using a gap-type forest model interfaced with a wood product model. The assessment is based on total carbon sequestration, i.e. the amount of carbon left in vegetation, litter, soil organic matter and products when the flows of carbon back to the atmosphere have been subtracted. Thirty mixed-species stands, representing medium fertility sites in southern Finland, were included in each simulation for 300 years under current climatic conditions and predicted conditions of changing climate. The average total balance for the first 100 years was higher in the unmanaged system than in the managed system, but for the second and third 100-year periods the results were clearly opposite. Differences in the total balance between the treatments were larger during the first 100 years than over the whole 300-year period. Under conditions of changing climate, differences in carbon sequestration between management options were more pronounced than under current climatic conditions. Under current climatic conditions with the 100-year time frame, the ratio between the total annual balance and annual gross production was 0·208–0·289. Over the whole 300 years, however, efficiency was much lower, 0·088–0·121. Under changing climatic conditions, efficiency was also lower, 0·182–0·252 and 0·081–0·096, respectively. Different management alternatives clearly produced different amounts of timber for the production process; under conditions of changing climate, timber production was substantially enhanced. However, total carbon storages at the end of the simulation varied less than timber production. In the managed system, the flow back into the atmosphere was largest from litter, 41–51% of the total outflow, the flow from vegetation was 23–28%, from soil organic matter 22–25%, emissions from products 1–7%, and emissions from landfills 0–3%. If emissions due to the use of machinery in timber harvesting and transportation were included, they made up only 0·03–0·33% of the total outflow.     

Joint implementation: Biodiversity and greenhouse gas offsets

One of the most pressing environmental issues today is the possibility that projected increases in global emissions of greenhouse gases from increased deforestation, development, and fossil-fuel combustion could significantly alter global climate patterns. Under the terms of the United Nations Framework Convention on Climate Change, signed in Rio de Janeiro during the June 1992 Earth Summit, the United States and other industrialized countries committed to balancing greenhouse gas emissions at 1990 levels in the year 2000. Included in the treaty is a provision titled Joint Implementation, whereby industrialized countries assist developing countries in jointly modifying long-term emission trends, either through emission reductions or by protecting and enhancing greenhouse gas sinks (carbon sequestration). The US Climate Action Plan, signed by President Clinton in 1993, calls for voluntary climate change mitigation measures by various sectors, and the action plan included a new program, the US Initiative on Joint Implementation. Wisconsin Electric decided to invest in a Jl project because its concept encourages creative, cost-effective solutions to environmental problems through partnering, international cooperation, and innovation. The project chosen, a forest preservation and management effort in Belize, will sequester more than five million tons of carbon dioxide over a 40-year period, will become economically selfsustaining after ten years, and will have substantial biodiversity benefits.     

The prognostic factors in the prenatal diagnosis of the echogenic fetal lung

The prenatal diagnosis of an echogenic fetal lung (EFL) is now often made in the early second trimester using high-resolution ultrasound. This ultrasound appearance is usually caused by a congenital cystic adenomatoid lung malformation (CCAM), an intrapulmonary lung sequestration or obstruction of a major airway. In order to provide prognostic guidelines to parents who may be considering termination of a fetus with these findings, we have analysed a series of 11 cases diagnosed in our centre over the past 2 years in conjunction with 60 cases from major published series. The data suggest that in the absence of non-immune hydrops fetalis (NIHF) or other anomalies, the outcome for the fetuses is excellent, with over 90 per cent survival. Neither early diagnosis (24 weeks) nor the presence of mediastinal shift is a poor prognostic indicator. In addition, it appears that if NIHF is absent at diagnosis, the chance that it will develop as the pregnancy continues is small (6 per cent). Furthermore, there is a significant (up to 30 per cent) chance that this ultrasound finding will resolve in utero. The development of in utero fetal surgical techniques may be the only hope for those hydropic fetuses who appear to have a dismal prognosis.     

Optimizing carbon sequestration in commercial forests by integrating carbon management objectives in wood supply modeling

This paper provides a methodology for generating forest management plans, which explicitly maximize carbon (C) sequestration at the forest-landscape level. This paper takes advantage of concepts first presented in a paper by Meng et al. (2003; Mitigation Adaptation Strategies Global Change 8:371–403) by integrating C-sequestration objective functions in existing wood supply models. Carbon-stock calculations performed in Woodstock^TM (RemSoft Inc.) are based on C yields generated from volume table data obtained from local Forest Development Survey plots and a series of wood volume-to-C content conversion factors specified in von Mirbach (2000). The approach is used to investigate the impact of three demonstration forest-management scenarios on the C budget in a 110,000 ha forest in south-central New Brunswick, Canada. Explicit demonstration scenarios addressed include (1) maximizing timber extraction either by clearcut or selection harvesting for greatest revenue generation, (2) maximizing total C storage in the forest landscape and in wood products generated from harvesting, and (3) maximizing C storage together with revenue generation. The level of clearcut harvesting was greatest for scenario 1 (≥15 × 10⁴ m³ of wood and ≥943 ha of land per harvesting period), and least for scenario 2 (=0 m³ per harvesting period) where selection harvesting dominated. Because softwood saw logs were worth more than pulpwood ($60 m⁻³ vs. $40 m⁻³) and were strategic to the long-term storage of C, the production of softwood saw logs exceeded the production of pulpwood in all scenarios. Selection harvesting was generally the preferred harvesting method across scenarios. Only in scenario 1 did levels of clearcut harvesting occasionally exceed those of selection harvesting, mainly in the removal of old, dilapidated stands early in the simulation (i.e., during periods 1 through 3). Scenario 2 provided the greatest total C-storage increase over 80 years (i.e., 14 × 10⁶ Mg C, or roughly 264 Mg ha⁻¹) at a cost of $111 per Mg C due to lost revenues. Scenarios 3 and 1 produced reduced storage rates of roughly 9 × 10⁶ Mg C and 3 × 10⁶ Mg C, respectively; about 64% and 22% of the total, 80-year C storage calculated in scenario 2. The bulk of the C in scenario 2 was stored in the forest, amounting to about 76% of the total C sequestered.     

Role of Bio-Energy Plantations for Carbon-Dioxide Mitigation with Special Reference to India

Fuelwood plays an important role in the rural economy of the developing countries of Asia and Africa. Optimizing energy fixation in forest trees through high density energy plantations (HDEP), gasification of wood, and conversion of forest tree biomass, are some of the potential areas whereby additional research and development input for efficient management of atmospheric carbon in our energy system can be incorporated. For example, the photosynthetic efficiency of forest trees is rarely above 0.5%, which on the basis of theoretical considerations can be increased by up to 6.6%. Thus there is an ample scope to improve the efficiency up to 1%, which amounts to doubling of the productivity of the forests. Recent policy changes and experiences with wood-based bio-energy programmes in several countries indicate that woodfuels may become increasingly attractive as industrial energy sources. Use of biodiesel and the formulation of a project for undertaking 13.4 million ha of Jatropha plantations in India highlight the seriousness with which the Government of India is promoting carbon neutral energy plantations. The cost of establishment of plantations primarily for fuel production and its conversion to energy are major deterrents in this pursuit. Some of the issues in developing countries, like low productivity on marginal lands, degraded forest lands, and unorganized units for biomass energy conversion, result in cost escalation as compared to other energy sources. This paper revisits the scope for raising energy plantations, a comparison of the direct and indirect mitigation potential uses of plantations as an adaptation strategy through reforestation and afforestation projects for climate change mitigation and socio-economic issues to make this venture feasible in developing countries.     

Baseline Carbon Stocks Assessment and Projection of Future Carbon Benefits of a Carbon Sequestration Project in East Timor

Climate change is one of the most pressing environmental problems humanity is facing today. Forest ecosystems serve as a source or sink of greenhouse gases, primarily CO₂. With support from the Canadian Climate Change Fund, the Community-based Natural Resource Management for Carbon Sequestration project in East Timor (CBNRM-ET) was implemented to “maintain carbon (C) stocks and increase C sequestration through the development of community-based resource management systems that will simultaneously improve livelihood security”. Project sites were in the Laclubar and Remexio Sub-districts of the Laclo watershed. The objective of this study was to quantify baseline C stocks and sequestration benefits of project components (reforestation with fast-growing species, primarily Casuarina equisetifolia, and agroforestry involving integration of Paraserianthes falcataria). Field measurements show that mature stands (≥30 years) of P. falcataria and C. equisetifolia contain up to 200 Mg C ha⁻¹ in above ground biomass, indicating the vast potential of project sites to sequester carbon. Baseline C stocks in above ground biomass were very low in both Laclubar (6.2 Mg C ha⁻¹ for reforestation sites and 5.2 Mg C ha⁻¹ for agroforestry sites and Remexio (3.0 Mg C ha⁻¹ for reforestation and 2.5 Mg C ha⁻¹ for agroforestry). Baseline soil organic C levels were much higher reaching up to 160 Mg C ha⁻¹ in Laclubar and 70 Mg C ha⁻¹ in Remexio. For the next 25 years, it is projected that 137 671 Mg C and 84 621 Mg C will be sequestered under high- and low C stock scenarios, respectively.     

Integrating agricultural and forestry GHG mitigation response into general economy frameworks: Developing a family of response functions

An econometrically estimated family ofresponse functions is developed forcharacterizing potential responses togreenhouse gas mitigation policies by theagriculture and forestry sectors in theU.S. The response functions are estimatedbased on results of anagricultural/forestry sector model. Theyprovide estimates of sequestration andemission reductions in forestry andagriculture along with levels of sectoralproduction, prices, welfare, andenvironmental attributes given a carbonprice, levels of demand for agriculturalgoods, and the energy price. Sixalternative mitigation policiesrepresenting types of greenhouse gasoffsets allowed are considered. Resultsindicate that the largest quantity ofgreenhouse gas offset consistently appearswith the mitigation policy that pays forall opportunities. Restricting carbonpayments (emission tax or sequestrationsubsidy) only to aff/deforestation or onlyto agricultural sequestration substantiallyreduces potential mitigation. Highercarbon prices lead to more sequestration,less emissions, reduced consumer and totalwelfare, improved environmental indicatorsand increased producer welfare.     

Effects of Oxalis pes-caprae L. invasion in olive groves

The present work aimed at studying the effect of Oxalis pes-caprae invasion in the herbaceous understory of olive groves in the island of Lesvos, Greece. The number of species, their biomass and dead plant material production was followed throughout the vegetative period in invaded and non-invaded plots. Species richness in the area invaded by O. pes-caprae gradually declined and was significantly smaller in comparison with the natural vegetation. Although biomass was equal in the invaded and non-invaded areas 1 month after germination, annual net primary production (NPP) was three times smaller in the invaded than the non-invaded area. Moreover, aboveground dead plant material of O. pes-caprae decomposed faster than a mixture of litter species of the natural vegetation. Lower biomass production in combination with increased decomposition rates of O. pes-caprae is expected to lead to reduced soil C sequestration in invaded areas. It was concluded that although O. pes-caprae does not add a new life form or functional type to the invaded herbaceous system it has considerable impacts on the diversity and ecosystem functions in olive groves.     

Uptake and metabolism of [<Superscript>14</Superscript>C]rinderine and [<Superscript>14</Superscript>C]retronecine in leaf-beetles of the genus <Emphasis Type="Italic"> Platyphora</Emphasis> and alkaloid accumulation in the exocrine defensive secretions

Summary. Sequestration and processing of pyrrolizidine alkaloids (PAs) by leaf beetles of the genus Platyphora were investigated. Tracer experiments with labeled alkaloids were performed with P. eucosma feeding on Koanophyllon panamense (Asteraceae, tribe Eupatorieae). P. eucosma catalyzes the same reactions previously demonstrated for P. boucardi specialized to Prestonia portobellensis (Apocynaceae): (i) epimerization of rinderine to intermedine; (ii) esterification of retronecine yielding insect-specific PAs; (iii) efficient transport of the PAs as free bases into the defensive secretions. P. bella feeding on Tournefortia cuspidata (Boraginaceae) shows the same sequestration behavior and ability to synthesize the specific retronecine esters. P. ligata, a species phylogenetically closely related to the PA adapted species and clustering in the same clade, but feeding on a host plant devoid of PAs, feeds easily on PA treated host-plant leaves, but does not sequester or metabolize PAs. P. kollari a species clustering outside the PA clade refused to feed on its food-plant leaves painted with PAs. The results are discussed in relation to host-plant selection of the PA adapted species and the role of PAs in chemical defense. Received 20 September 2002; accepted 18 November 2002.