Holocene fire and vegetation dynamics in a montane forest, North Cascade Range, Washington, USA     

Susan J. Prichard  Ze'ev Gedalof 《Quaternary Research》2009,72(1):57-67

We reconstructed a 10,500-yr fire and vegetation history of a montane site in the North Cascade Range, Washington State based on lake sediment charcoal, macrofossil and pollen records. High-resolution sampling and abundant macrofossils made it possible to analyze relationships between fire and vegetation. During the early Holocene (> 10,500 to ca. 8000 cal yr BP) forests were subalpine woodlands dominated by Pinus contorta. Around 8000 cal yr BP, P. contorta sharply declined in the macrofossil record. Shade tolerant, mesic species first appeared ca. 4500 cal yr BP. Cupressus nootkatensis appeared most recently at 2000 cal yr BP. Fire frequency varies throughout the record, with significantly shorter mean fire return intervals in the early Holocene than the mid and late Holocene. Charcoal peaks are significantly correlated with an initial increase in macrofossil accumulation rates followed by a decrease, likely corresponding to tree mortality following fire. Climate appears to be a key driver in vegetation and fire regimes over millennial time scales. Fire and other disturbances altered forest vegetation at shorter time scales, and vegetation may have mediated local fire regimes. For example, dominance of P. contorta in the early Holocene forests may have been reinforced by its susceptibility to frequent, stand-replacing fire events.  相似文献   

“火珠”的宝石学成分探讨     

李国忠 《地质科学译丛》2009,(4):45-49

在佛经与我国史籍中均记载有一种名为＂火珠＂的宝石,但其宝石学成分究竟是什么,历来争论颇大。三国时期,＂火珠＂开始从外国进口,被帝王看作是祥瑞的标志。晋代时期其用于装饰皇太子的玉具剑。隋唐时期,其价值进一步提升,专用于装饰皇帝的玉具剑。自唐朝末年开始,＂火珠＂一词的宝石学意义逐渐减弱。探讨＂火珠＂有助于了解中国古代宝石的使用情况,对构建中国古代宝石学具有重要意义。从＂火珠＂的产地、颜色、稀有性等宝石学特征以及与出土宝石实物比照,对其成分进行了较详细的论证。结果发现,＂火珠＂是巴利文＂Phalika＂（＂颇黎＂）以及梵文＂Sphatika＂（＂塞颇胝迦＂）的意译。＂火珠＂也就是＂颇黎＂,并不是我国常见的水晶,最可能为无色刚玉。  相似文献   

Nonlinear incremental analysis of fire-damaged r.c. base-isolated structures subjected to near-fault ground motions     

《Soil Dynamics and Earthquake Engineering》2015

Amplification of structural response of r.c. base-isolated structures is expected under near-fault ground motions, yet there is a lack of knowledge of their behavior in the case of fire. To investigate the nonlinear seismic response following a fire, an incremental dynamic analysis is carried out on five-storey r.c. base-isolated framed buildings with fire-protected High-Damping-Laminated-Rubber Bearings (HDLRBs), designed in line with the Italian seismic code. Horizontal components of near-fault ground motions characterized by forward-directivity or fling-step pulse-type are considered. The nonlinear seismic response of base-isolated structures in a no fire situation is compared with that in the event of fire, at 45 (i.e. R45) and 60 (i.e. R60) minutes of fire resistance, assuming both damaged (i.e. DS) and repaired (i.e. RS) stiffness conditions. Five fire scenarios are considered assuming the fire compartment confined to the area of the first level (i.e. F1), the first two (i.e. F1/2) and the upper (i.e. Fi, i=3–5) levels, with the parametric temperature–time fire curve evaluated in accordance with Eurocode 1. The nonlinear seismic analysis is performed by using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the critical (end) sections of the girders and columns, where thermal mapping with reduced mechanical properties is evaluated with the 500 °C isotherm method proposed by Eurocode 2. A viscoelastic model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, simulates the response of an HDLRB.  相似文献   

高大空间消防电气设计——山西省图书馆火灾报警系统设计实例简介     

许琳 《中国勘察设计》2009,(8):62-64

文章介绍了山西省图书馆火灾报警系统设计实例。针对建筑物中庭的高大空间,采用双波段火灾探测器,有效探测火灾火焰和火灾烟气;采用微机信息处理系统构成了集火灾识别、火灾定位、现场监控、消防炮扑救于一体的火灾安全监控及联动灭火系统;同时辅以搭建于闭路电视监控系统平台上的视频火灾安全监控系统,满足了图书馆建筑对于早期火灾报警的特殊需要。  相似文献   

Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron     

Encarni Montoya  Valenti Rull  Nathan D. Stansell  Broxton W. Bird  Sandra Nogué  Teresa Vegas‐vilarrúbia  Mark B. Abbott  Wilmer A. Díaz 《第四纪科学杂志》2011,26(2):207-218

The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 °N, 61.0157 °W, 884 m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from ～15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200 m elevation above the lake, suggesting a cooling‐driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

火烧对湿地生态系统影响研究进展   总被引：3，自引：0，他引：3  

赵红梅  于晓菲  王健  王国平 《地球科学进展》2010,25(4):374-380

火烧对湿地生态系统的影响是国内外火生态学和湿地生态系统研究中的一个热点。综述了国内外关于火烧对湿地生态系统各组成部分影响的研究进展,总结了湿地火烧的特点,火烧对湿地植物生长发育、群落特征的影响,火烧对土壤理化性质、对土壤中碳氮等元素形态及分布特征的影响。并针对目前湿地火烧在研究内容和方法上存在的问题,结合国外研究特点,提出了今后国内湿地火烧的研究展望。  相似文献   

A signal-to-noise index to quantify the potential for peak detection in sediment-charcoal records     

Ryan F. Kelly  Philip E. Higuera  Feng Sheng Hu 《Quaternary Research》2011,75(1):11-17

Charcoal peaks in lake-sediment records are commonly used to reconstruct fire histories spanning thousands of years, but quantitative methods for evaluating the suitability of records for peak detection are largely lacking. We present a signal-to-noise index (SNI) that quantifies the separation of charcoal peaks (signal) from other variability in a record (noise). We validate the SNI with simulated and empirical charcoal records and show that an SNI > 3 consistently identifies records appropriate for peak detection. The SNI thus offers a means to evaluate the suitability of sediment-charcoal records for reconstructing local fires. MATLAB and R functions for calculating SNI are provided.  相似文献   

Four thousand years of environmental change and human activity in the Cochabamba Basin, Bolivia     

Joseph J. Williams  William D. Gosling  Stephen J. Brooks 《Quaternary Research》2011,76(1):58-126

The Cochabamba Basin (Bolivia) is on the ancient road network connecting Andean and lowland areas. Little is known about the longevity of this trade route or how people responded to past environmental changes. The eastern end of the Cochabamba valley system constricts at the Vacas Lake District, constraining the road network and providing an ideal location in which to examine past human-environmental interactions. Multi-proxy analysis of sediment from Lake Challacaba has allowed a c. 4000 year environmental history to be reconstructed. Fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability (c. 4000-3370 and c. 2190-1020 cal yr BP) compared to adjacent wetter episodes (c. 3370-2190 and c. 1020 cal yr BP-present). The moisture fluctuations broadly correlate to El Niño/Southern Oscillation variations reported elsewhere. High charcoal abundance from c. 4000 to 2000 yr ago indicates continuous use of the ancient road network. A decline in charcoal and an increase in dung fungus (Sporormiella) c. 1340-1210 cal yr BP, suggests that cultural changes were a major factor in shaping the modern landscape. Despite undisputable impacts of human populations on the Polylepis woodlands today, we see no evidence of woodland clearance in the Challacaba record.  相似文献   

Charcoal signatures defined by multivariate analysis of charcoal records from 10 lakes in northwest Wisconsin (USA)     

Elizabeth A. Lynch  Sara C. Hotchkiss 《Quaternary Research》2011,75(1):125-137

We show how sedimentary charcoal records from multiple sites within a single landscape can be used to compare fire histories and reveal small scale patterns in fire regimes. Our objective is to develop strategies for classifying and comparing late-Holocene charcoal records in Midwestern oak- and pine-dominated sand plain ecosystems where fire regimes include a mix of surface and crown fires. Using standard techniques for the analysis of charcoal from lake sediments, we compiled 1000- to 4000-yr-long records of charcoal accumulation and charcoal peak frequencies from 10 small lakes across a sand plain in northwestern Wisconsin. We used cluster analysis to identify six types of charcoal signatures that differ in their charcoal influx rates, amount of grass charcoal, and frequency and magnitude of charcoal peaks. The charcoal records demonstrate that while fire histories vary among sites, there are regional patterns in the occurrence of charcoal signature types that are consistent with expected differences in fire regimes based on regional climate and vegetation reconstructions. The fire histories also show periods of regional change in charcoal signatures occurring during times of regional climate changes at ~ 700, 1000, and 3500 cal yr BP.  相似文献   

Disentangling Fabiana imbricata (Solanaceae) regeneration: The importance of disturbance and rainfall     

《Journal of Arid Environments》2013

In Mediterranean ecosystems, fire influences plant population dynamics and changes plant community structure by affecting germination and establishment of seeder shrubs. Fabiana imbricata is a long-lived seeder shrub with a broad distribution in South America. In Northwestern Patagonia grasslands there are many records of F. imbricata recruitment after fires. We hypothesized that recruitment is promoted by: 1) soil erosion that exposes deeply buried seeds; 2) direct fire effects such as heat that could break seed dormancy; 3) indirect fire effects (i.e. increase of light availability and elimination of allelopathic substances) and 4) water availability in spring. In field conditions, we tested the effects of shading and soil disturbance on F. imbricata recruitment and seed availability and distribution in the soil profile. Under controlled conditions, we investigated the influence of leaf leachate, light, heat and water on seed germination and seedling emergence. Seed germination was inhibited by leachate, and seedling emergence was inhibited by seed heated to 80 °C and 120° for 5 min. F. imbricata seedlings only emerged in germination treatments that simulated wet and very wet spring conditions. Fire and postfire wind that favor seed exposure, combined with high precipitation early in the growing season, would be necessary for successful shrub recruitment. When F. imbricata shrubland colonizes the grassland, it strongly modifies local vegetation structure, reduces species richness and increases fuel loads. F. imbricata is a key species in the ecosystem specially related to fire regime. Information on the postfire regeneration of this species would provide valuable knowledge of the changes in biomass accumulation in a fire-prone Mediterranean ecosystem.  相似文献