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61.
How Climate and Vegetation Influence the fire Regime of the Alaskan Boreal Biome: The Holocene Perspective 总被引:2,自引:0,他引:2
Feng Sheng Hu Linda B. Brubaker Daniel G. Gavin Philip E. Higuera Jason A. Lynch T. Scott Rupp Willy Tinner 《Mitigation and Adaptation Strategies for Global Change》2006,11(4):829-846
We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal
ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with
the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred
at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should
not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable
P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests
dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where
fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of
P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime
and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial
array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation
remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will
require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge
of how sedimentary charcoal records fire events.
In this paper, charcoal refers to macroscopic (≥180 μm) as opposed to microscopic (< 180 μm) particles unless indicated otherwise.
Radiocarbon ages were converted to calibrated years before AD 1950 using the atmospheric calibration data set (Stuiver et
al. 1998). 相似文献
62.
简要介绍溶解氧自动监测在石化污水处理场的成功运用,并着重指出优化污水处理主要工艺参数的自动监测是不可缺少的重要措施。在缺氧池和两级好氧池安装的两套溶解氧自动监测仪,使监测人员根据已测得的溶解氧数据调节曝气量,既降低了能耗,又为好氧生物提供了优良的生活条件,使多群好氧生物的活力增强,提高了对污水中有机物的降解能力,使总排合格率稳定提高。 相似文献
63.
64.
通过对塔克拉玛干沙漠北部,塔里木河泛滥平原典型剖面的沉积物粒度特征、化学元素的变化和沉积相特征的研究,并结合~(14)C测年,揭示了本区域全新世以来的环境变化规律,本区全新世以来的多风、高温、干燥的气候形成是以全球气候波动为背景,叠加内陆干旱封闭盆地影响而成的。但在干燥气候条件下曾有过几次空气湿度较大的偏湿期。本区沉积相主要以河流冲积作用形成的粘土层和风力作用下形成的风砂层为主,剖面中的亚粘土与现代河流相特征一致,剖面中风砂土与现代流沙性质趋同。全新世以来本区共发生3次明显的河流泛滥期,可以同全新世以来的间冰期对应。 相似文献
65.
A comprehensive study of paleobotanical materials collected in the northern part of the Eastern Sayan was performed, including botanical analysis of peat, palynological and carpological analysis, and radiocarbon dating. The results provided a basis for reconstructing in detail the spatiotemporal distribution of ecocenotic complexes and corresponding paleoclimate types and calculating quantitative gradients of heat and moisture supply in the Late Holocene, beginning from 3500 ka. 相似文献
66.
Aarno T. Kotilainen Laura Arppe Slawomir Dobosz Eystein Jansen Karoline Kabel Juha Karhu Mia M. Kotilainen Antoon Kuijpers Bryan C. Lougheed H. E. Markus Meier Matthias Moros Thomas Neumann Christian Porsche Niels Poulsen Peter Rasmussen Sofia Ribeiro Bjørg Risebrobakken Daria Ryabchuk Semjon Schimanke Ian Snowball Mikhail Spiridonov Joonas J. Virtasalo Kaarina Weckström Andrzej Witkowski Vladimir Zhamoida 《Ambio》2014,43(1):60-68
Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change. 相似文献
67.
Kirk R. Smith 《Environmental management》1986,10(1):61-74
About half the world's households cook and/or heat daily with biomass fuels. At small scale, biomass combustion releases significant amounts of particulates, carbon monoxide, and hydrocarbons, the latter with significant concentrations of polycyclic aromatic hydrocarbons. Preliminary measurements in kitchens of developing-country villages have established airborne concentrations of these healthdamaging pollutants that are orders of magnitude above urban levels or relevant standards. Particle size measurements and dose calculations lead to significant concerns about potential health hazards. The few epidemiological studies are consistent with such effects although more work is clearly needed. These findings may have significant implications for the planning of rural energy development in a number of countries. In particular, they may relate directly to the question of the optimum balance between centralized and decentralized systems. 相似文献
68.
69.
华北平原东部全新世古年地表径流量的估算 总被引:1,自引:0,他引:1
利用以现代数据建立的年平均降水量、年平均温度与年平均地表径流深间的关系式和全新世古年降水量、古年温度的推测值估算了华北平原东部的全新世古年地表径流深,并将估算结果与已有的古水文数据作了对比。 相似文献
70.
Mitochondrial DNA (mtDNA) variation has been studied in populations of the Siberian larch with the use of five PCR-based markers characterizing 29 haplotypes. The studied populations from the main parts of the Siberian larch range belong to several geographically isolated groups with their specific sets of haplotypes, which have probably originated from separate refugia for forest vegetation of the last glacial maximum. Conclusions concerning the possible location of these refugia and the ways and pattern of the postglacial recolonization of the recent Siberian larch range are drawn. The spatial distribution of haplotypes within individual populations is nonrandom. The typical size of the area occupied by a group of plants with the same haplotype is 50–100 m across. 相似文献