林分尺度上的森林火灾风险评估方法及应用

[目的]基于森林燃烧概率、潜在火行为和火影响评估一个区域的森林火灾风险是有效开展林火管理的基础。[方法]利用森林燃烧概率模拟软件(Burn-P3)模拟了北京九龙山林场的燃烧概率、潜在火强度、蔓延速度及火发生类型。根据林场内各林班的生态重要性、生态脆弱性和保护等级确定火影响,并考虑火对周围城镇和水源的潜在影响,利用层次分析方法建立了林分尺度上的森林火灾风险评估体系。[结果]结果表明,研究区的平均燃烧概率为0.0351,燃烧概率高和很高的区域分别占研究区的10.3%和6.0%。火烧以地表火和间歇性树冠火为主,平均火强度及蔓延速度分别为2140.9 kW·m^(-2)和3.7 m·min^(-1)。火行为指数高和很高的区域分别占17.8%和14.0%。[结论]研究区森林生态价值和火对环境的影响较高。森林火灾风险评估结果显示,火灾风险高和很高的区域占31.8%。西部、北部及南部的落叶松林和混交林的火灾风险较高,未来需要加强针对性的林火管理。

Nitrogen Mineralization in Soils Along a Vegetation Chronosequence in Hong Kong

This research examined nitrogen mineralization in the top 10 cm of soils along a vegetation gradient in Hong Kong at sites where fire has been absent for 0, 1, 3, 6 and 17 years (at the time of the study), and the relationships between N mineralization and successional development of vegetation in the absence of fire. The sites including a newly burnt area (S1), short grassland (S2), tall grassland (S3), mixed tall grassland and shrubland (S4), and woodland (S5) were selected,and the in situ core incubation method was used to estimate nitrogen mineralization. Throughout the 60-day incubation in four periods, more nitrogen was mineralized at the S3 and S4 sites, the predominantly grassland sites, which contained the highest levels of soil organic matter (SOM) and total Kjeldahl nitrogen (TKN), than the S1 site, while immobilization occurred at the S2 and S5 sites. Leaching loss decreased with successional development of the vegetation, in the order of S1 ＞ S2 ＞ S3 ＞ S4 ＞ S5. The pattern of nitrogen uptake with ecological succession was less conspicuous, being complicated by the immediate effect of fire and possibly the ability of the woodland species to extract nitrogen from the deeper ground.In the absence of fire for 3 to 6 years, the build-up of SOM and TKN was accompanied by active mineralization, thus paving the way for the invasion of shrub and tree species. A close relationship existed between nitrogen mineralization and ecological succession with this vegetation gradient. Inherent mechanisms to preserve nitrogen in a fire-prone environment including immobilization and uptake and the practical relevance of nitrogen mineralization to reforestation are discussed.

Episodes of volcanic activity and their environmental effects in the Okinawa Trough during the last 150 ka

A piston core Z14-6 was used in this study. The core, 896 cm long, was collected from eastern slope of the Okinawa Trough （27°07＇N, 127°27＇E, water depth 739m）. The δ^18O and δ^13C values of the sediment bearing planktonic foraminifera G. sacculifer and N. dutertrei were determined; and the abundance of volcanic glass was analyzed. The volcanic glass content high occurred in early stage of polar ice-sheet growth period, or the beginning of cold climate periods corresponding to Milankovitch cycles （Peak Ⅰ, Ⅱ and V are corresponding to the beginnings of oxygen isotopic stages 2, 4 and 6, and Peak Ⅲ and Ⅳ are matching oxygen isotopic stage 5b-5d.）. It might be possible that volcanic episodes and climate changes were responding to orbital forcing in the Okinawa Trough in late Quaternary. The δ^18O difference between N. dutertrei and G. sacculifer shows no clear correlation to the volcanic glass content high, which suggests that the volcanic eruptions did not influence the structure of upper water column. However, the low δ^13C difference between G. sacculifer and N. dutertrei is coeval with the volcanic glass high or sub-high content. This fact suggests that volcanic eruptions might influence the reduction in vertical nutritional gradient and carbon cycle process in upper water column. A possible mechanism is that huge quantity of ash and dust had weakened the light intensity, resulting in photosynthesis reduction, productivity decrease, and biological pumping.

Effect of inlet temperature and equivalence ratio on HCCI engine performance fuelled with ethanol:Numerical investigation

A numerical model is presented to investigate the performance of homogeneous charge compression ignition(HCCI) engines fueled with ethanol. Two approaches are studied. On one hand, two-step reaction mechanisms with Arrhenius reaction rates are implemented in combustion chemistry modeling. On the other hand, a reduced mechanism containing important reactions of ethanol involving heat release rate and reaction rates compatible with experimental data is employed. Since controls of combustion phenomenon and ignition timing are the main issues of these engines, the effects of inlet temperature and equivalence ratio as the controlling factors on the operating parameters such as ignition timing, burn duration, in-cylinder temperature and pressure of HCCI engines are explored. The results show that the maximum predicted pressures for thermodynamic model are about 71.3×10~5 Pa and 79.79×10~5 Pa, and for chemical kinetic model, they are about 71.48×10~5 Pa and 78.123×10~5 Pa, fairly comparable with corresponding experimental values of 72×10~5 Pa and 78.7×10~5 Pa. It is observed that increasing the initial temperature advances the ignition timing, decreases the burn duration and increases the peak temperature and pressure. Moreover, the maximum temperature and pressure are associated with richer mixtures.

Fire risk evaluation research on fully mechanized coalface based on the uncertainty measure theory

A relatively perfect coalmine fire risk-evaluating and order-arranging model that includes sixteen influential factors was established according to the statistical information of the fully mechanized coalface ground on the uncertainty measure theory. Then the single-index measure function of sixteen influential factors and the calculation method of computing the index weight ground on entropy theory were respectively established. The value assignment of sixteen influential factors was carried out by the qualitative analysis and observational data, respectively, in succession. The sequence of fire danger class of four experimental coalfaces could be obtained by the computational aids of Matlab according to the confidence level criterion. Some conclusions that the fire danger class of the No.l, No.2 and No.3 coalface belongs to high criticality can be obtained. But the fire danger class of the No.4 coalface belongs to higher criticality. The fire danger class of the No.4 coalface is more than that of the No.2 coalface. The fire danger class of the No.2 coalface is more than that of the No.1 coalface. Finally, the fire danger class of the No.1 coalface is more than that of the No.3 coalface.

Blood Lead Levels During Pregnancy and Its Influencing Factors in Nanjing,China

Objective To investigate the blood lead levels （BLLs） in the duration of pregnancy and 6-12 weeks after delivery, and analyze the influencing factors of BLLs in healthy pregnant women. Methods Pregnant women were recruited from September 2009 to February 2010 at the prenatal clinic in Nanjing Maternity and Child Health Care Hospital. Altogether 174 healthy pregnant women without pregnant or obstetric complications or abnormal pregnancy outcomes were enrolled as the gravida group, and 120 healthy non-pregnant women as the control group. BLLs during pregnancy were determined by flame atomic absorption spectroscopy. Results BLLs in all the three pregnancy trimesters and postpartum were 59.8±24.3, 55.4±20.1, 55.9±19.7, and 67.6±17.4 μ/L, respectively, and the mean BLL in control group was 67.5±21.3 μg/L. BLLs during all the three trimesters were lower in the gravida group than in the control group （P=0.043, 0.021, and 0.028）. Furthermore, occupations, nutrients supplementation, and time of house/apartment painted were associated with BLLs in pregnant women. Lead-related occupations, cosmetics use, and living in a house painted less than 1 year before are risk factors of high BLLs among pregnant women, while calcium, iron, zinc, and milk supplements are protective factors. Conclusion Supplementing calcium, iron, zinc, and milk, or avoiding contact with risk factors may help people, especially pregnant women, to reduce lead exposure.

栎类林对火的适应和响应研究进展

近年来,由于人类活动的影响,加之极端天气常现,森林火灾呈现持续多发且频发的趋势,火格局(发生季节、频率、强度等)也发生相应改变。尽管栎类林出现了各种不同频率和强度的火灾,但大多数栎类已经进化出能够在周期性火灾中生存的能力。需要明确栎类对森林火灾的响应,进而揭示栎类对火的适应性策略。本文从栎类林特征、燃烧性、栎类植物自然更新以及个体和种群对火干扰的适应与响应等方面入手,论述了栎类林对火的适应与响应,对其现存研究问题进行了分析,并对未来的研究方向进行了展望。研究结果能够为生态恢复树种选择、防火树种筛选、生物防火林带营建等提供科学依据,有利于我国栎类的适地适树造林和管护,特别有利于火灾频发多发区域选择抗火性强的栎类树种;有利于对栎类的分类经营和管理,提高生产力;有利于栎类的高效综合利用,发挥生态、经济和社会效益。

Physiological Effect on Hylocereus undulatus and Hylocereus undatus under Simulated Karst Soil Water Deficiency

Dragon fruit （Hylocereus undulates） was planted in a large area of karst region in recent years. To understand whether karst drought may impact on its physiological process is important and useful for planning and management of this fruit. In this study, we contrasted with a relative species Hylocereus undatus, and set up experiment to study physiological and biochemical trait and its response to different karst soil water level deficiency, so as to understand the mechanism of H. undulates and H. undatus in adaptation to karst drought condition. The results showed that, trends of physiological and biochemical response to drought was similar between two species. With the intensive of soil water deficiency, such toxin substance as malonaldehyde （MDA） increased, but meanwhile, two protective enzymes superoxide dismutase （SOD） and peroxidases （POD） and osmotic adjustment Proline （Pro） increase as well. Under relative water content （RWC） 〉50% condition, the enzyme can effectively protect the cells from toxin MDA injure, and Pro can also maintain the water needs through osmotic adjustment. However, under RWC 〈 40% condition, protective enzymes were not enough for cleaning MDA. Biomass was largest under RWC=70%-80%, with low root shoot ratio and high aboveground biomass. Biomass significantly decreased under RWC 30%-40%, which decline by 73.28% and 73.56% in H. undulates and H. undatus respectively. Therefore, RWC=70%-80% would be an optimal soil moisture while developing dragon fruit in karst, which is favor to fruit production. Under moderate drought e.g. RWC=50%-60%, plants may regulate by metabolic process and balance unfavorable substance, but it allocated much more biomass to root, reduced the aboveground biomass, which is not advance for fruit production.