人为热源和城市绿化对冬季山谷城市边界层结构影响的数值模拟

为了探讨人为热源和城市绿化对城市边界层的影响,本文在RAMS模式中引入周期性日变化的人为热源和人工改变下垫面状况,初步模拟分析了人为热源和城市绿化对城市边界层结构的影响.结果表明:人为热源具有明显的增温效应,增强了城市的湍流交换,白天增加了大气不稳定度,促进了混合层的发展,夜间降低了大气稳定度,减弱了城市夜间逆温.城市绿化减小了地表反照率,增加了到达地面的净辐射,模拟期间土壤冻结,增加的净辐射其中一部分以感热的形式来加热大气;绿化后地气之间的湍流交换增强,增加了大气不稳定度,减弱了白天高空逆温;本文还讨论了不同绿化布局对白天高空逆温的影响以及人为热源和城市绿化之间的非线性相互作用.     

滩地抑螺防病林的营造技术

长江中下游大面积的滩地,由于开垦、放牧等严重的人为干扰,植被极度退化,并为血吸虫中间寄主钉螺的孳生地,如何有效防治血吸虫病和科学保护利用这些滩地一直是亟待解决的一大难题。我国林业科技工作者经过多年的研究,提出建立抑螺防病林,恢复滩地植被,改善滩地环境,控制钉螺密度,防止血吸虫病流行,提高滩地经营效益等一整套技术措施,成效显著。     

湛江红树林国家级自然保护区人工造林现状及造林技术探讨

红树林是一种生长在沿海潮间带的木本植物群落的总称。红树林具有多种不可替代的生态价值,它保护沿海居民免受台风侵袭、促淤造陆;同时,红树林还是各种海洋生物的家园,生物多样性极其丰富。近年来,湛江红树林保护区已连续造林约1500hm2。对有记录以来的人工造林进行了一次全面调查,评估了保护区内人工林生长现状并对雷州半岛红树林的造林技术进行了总结。     

Temporal Change of Runoff and Sediment Load and their Differential Response to Human Activities：A Case Study for a Well-vegetated Mountain Watershed of Southern China

This study examined the temporal trends of runoff and sediment load and their differential response to human activities in the Lishui river,a tributary of the Yangtze river in southern China.The long-term observation data at four gauging stations,generally involving two periods from 1954 to 1985 and from 2007 to 2011,were used.We detected no significant temporal trend for both the annual runoff volume（Q） and the annual suspended Sediment Load（SL） over more than 30 years before 1985.The flow duration curves and the Suspended Sediment Concentration（SSC） also hold constant before 1985.Compared with the period before 1985,SL has decreased by about 80% though Q remains unchanged for the period after 2007.Detailed examination shows that the flow duration curves after 2007 have changed with a significant decrease in the high-flow component,which acts as a major cause for the decreasing SL.In addition,SSC has decreased by several times,which also contributes to the decrease in SL after 2007.Both decreases in high-flow discharges and in SSC can be linked with recent human activities,mainly including vegetation establishment and dam constructions.The constant Q and the decreasing SL are also reported for the main stream of the Yangtze River and other major rivers in southern China,although they are orders of magnitude larger than our study area in drainage area size.The present study highlights the importance of high-flow discharges on SL and suggests that the use of SL is more appropriate to reflect environmental change than Q.     

Modelling long term stream acidification trends in upland wales at plynlimon

Historical reconstructions and predictions of streamwater acidification are presented for moorland and afforested catchments in the Welsh Uplands at Plynlimon. MAGIC (Model of Acidification of Groundwater In Catchments) is validated by application to an afforested catchment. MAGIC is used to illustrate that atmospheric deposition is primarily responsible for stream acidification but that conifer afforestation can enhance stream acidity. The historical trends determined by the model illustrate that long-term acidification has been present since the turn of the century and will continue unless either deposition levels are reduced significantly or liming is undertaken on a major scale.     

Afforestation of European landscapes: How do different farmer types respond to EU agri-environmental schemes?

This paper investigates how different types of farmers manage the landscape with primary emphasis on farmland afforestation, planned landscape changes, and the extent to which EU agri-environmental schemes take farm type specific characteristics into account in information strategies. The empirical data concern landscape practices of more than 2,000 landowners in 16 European areas in eight countries who were surveyed using quantitative questionnaires. Supplementary in-depth interviews were conducted for two case areas in Denmark to further investigate the role of the policy information environment. The analysis is based on a categorization of the farmers into hobby, part-time, full-time and retired farmers. This study shows that hobby farmers constitute a high proportion of landowners and manage a large part of the rural landscape. At the same time, hobby farmers are relatively more interested in landscape changes and differ from other landowners by considering farmland afforestation more often than full-time landowners, for example. Yet, 40% of the hobby farmers who are considering farmland afforestation are not familiar with the agri-environmental scheme for farmland afforestation. One reason may be their low membership rate in traditional information networks such as farmers’ or foresters’ associations, as revealed by the in-depth analysis of the cases in Denmark. Thus, it is proposed that policy impact may be improved if farmer type specific differences are explicitly taken into account in the scheme logistics for EU agri-environmental schemes.     

Bringing greenhouse gas removal down to earth: Stakeholder supply chain appraisals reveal complex challenges

Greenhouse gas removal (GGR) approaches are considered essential in several projections to meet the climate mitigation ambition of the Paris Agreement. Biomass Energy with Carbon Capture and Storage (BECCS) and afforestation are included extensively in mitigation scenarios but there are concerns about the feasibility of these approaches. This was explored with stakeholders from industry, non-governmental organisations (NGOs) and policy who were involved in interviews and a one-day participatory workshop. Multicriteria mapping (MCM) methodology was used to appraise the ‘real-world’ feasibility of four specific greenhouse gas removal supply chains at a granular level in the UK context. The MCM analysis shows that afforestation performs better in comparison to three BECCS supply chains, on criteria such as business model, social acceptability, and environmental sustainability. This innovative application of the MCM methodology enables the abstract representations of GGR in integrated assessment models to be explored at a more granular level through a supply chain analysis and thus gain a deeper understanding of the issues facing these approaches. The data gathered allows a wide range of technical, environmental, social and political criteria to be systematically applied in appraising the practical performance of different future implementation options for afforestation and BECCS. If these GGR supply chains are to become a reality on the scale required for 1.5 °C global warming, factors such as global cooperation, land availability, and the longevity of policies and incentives were found to be major challenges.     

Carbon sequestration in Africa: The land tenure problem

The prospect of using tropical forest projects to sequester significant amounts of atmospheric carbon as one mitigation approach to climate change has received considerable attention. In the Kyoto Protocol, the Clean Development Mechanism (CDM) aspires to make such projects viable. This article examines the prospect of these projects in Africa, and argues that land tenure is much more than just a set of variables to be changed, and that instead it exists as a prohibitive obstacle to the implementation of afforestation and reforestation sequestration approaches. Five primary tenure problems are examined: (1) the disconnect between customary and statutory land rights, (2) legal pluralism, (3) tree planting as land claim, (4) expansion of treed areas in smallholder land use systems, and (5) the difficulty of using the ‘abandoned land’ category. The pervasiveness of these tenurial issues mean that the prospects for successfully implementing afforestation and reforestation projects in Africa are in reality quite weak. The current project approach to carbon storage in Africa needs to be significantly realigned with African reality in order for sequestration expectations to be practical.     

Does grazing change algal communities from grassland and pine afforested streams?: A laboratory approach

Drastic changes in the composition and physiognomy of riparian vegetation, such as the conversion of grassland to forest, are expected to alter interactions among light availability, primary producers and herbivores. Our aim was to examine in laboratory the influence of a ubiquitous grazer on periphyton grown in a grassland unshaded stream (reference) vs. periphyton from a nearby pine afforested stream. Besides, we evaluated how the community responds to the removal of grazing. Given that grassland streams are exposed to higher light intensity and grazers are more abundant compared to afforested streams, we proposed that if biofilm grown in the afforested stream are dominated by grazing-vulnerable algal species, grazing pressure by Helicopsyche sp. should be stronger. In addition, if biofilm from the afforested stream has low quality or is less abundant as food for consumers, the effects of Helicopsyche sp. may be stronger or weaker depending on their feeding decisions. Helicopsyche sp. caused a decrease in richness and diversity in periphyton grown in the grassland stream and its net grazing effect on chlorophyll a (Chl a) was higher. Algal community composition from grassland stream was strongly changed after grazing, with a decrease in the proportion of overstory algae. In contrast, algal community structure of periphyton from the afforested stream was neither affected by grazing nor by grazing exclusion. Helicopsyche sp. produced significant changes in a short time in structural attributes of algal communities, mainly in periphyton from the grassland stream suggesting that herbivory, as a functional factor, is diminished following afforestation.     

Magnitude,distribution and causes of terrestrial carbon sinks and some implications for policy

Abstract

Recent analyses continue to modify our understanding of terrestrial carbon sinks. The sinks are large and variable enough to account for much of the variability in the growth rate of atmospheric CO₂. They are distributed throughout both northern mid-latitudes and the tropics. Identification of the factors influencing an observed sink is extremely difficult; methods for attribution are reviewed. Although various ecological mechanisms (e.g. CO₂ fertilization, nitrogen deposition, climatic variability) have been shown experimentally to have short-term effects on physiological processes controlling the amount of carbon in terrestrial ecosystems, it is unclear which of these mechanisms has been most important in the past 10–100 years and which will be most important in the future. The decades-long supposition that CO₂ fertilization has been a major driver of terrestrial carbon uptake is being challenged. A major portion of the sink in the northern mid-latitudes (although probably not in the tropics) is a result of recovery from past changes in land use and management. To the extent that these direct human actions explain most of the current (and future) sink, attribution and thus accounting become more tractable, but the continued functioning of the sink is limited and largely dependent on deliberate actions (e.g. afforestation, sustainable forest management and preservation).