Holocene climate–fire–vegetation interactions at a subalpine watershed in southeastern British Columbia,Canada     

Colin J. Courtney Mustaphi  Michael F.J. Pisaric 《Quaternary Research》2014

Vegetation assemblages and associated disturbance regimes are spatially heterogeneous in mountain ecosystems throughout the world due to the complex terrain and strong environmental gradients. Given this complexity, numerous sites describing postglacial vegetation and fire histories are needed to adequately understand forest development and ecosystem responses to varying climate and disturbance regimes. To gain insight into long-term historical climate–fire–vegetation interactions in southeastern British Columbia, Canada, sedimentological and paleoecological analyses were performed on a sediment core recovered from a small subalpine lake. The pollen assemblages, stomata, and macroremains indicate that from 9500 to 7500 cal yr BP, Pinus-dominated forests occurred within the catchment and Alnus was also present. Climate was an important control of fire and fire frequency was highest at this time, peaking at 8 fires 1000 yr^− 1, yet charcoal accumulation rates were low, indicative of low terrestrial biomass abundance. From 7500 to 4600 cal yr BP, Pinus decreased as Picea, Abies and Larix increased and fire frequencies decreased to 3–6 fires 1000 yr^− 1. Since 7500 cal yr BP the fire regime varied at a millennial scale, driven by forest biomass abundance and fuel accumulation changes. Local scale (bottom-up) controls of fire increased in relative importance since at least 6000 cal yr BP.  相似文献   

不同阶曲线拟合扰动场对下平流层重力波气候特征影响研究     

程胡华  王益柏  武帅  赵亮  智茂林 《气象学报》2021,79(2):240-254

重力波参数气候特征是确定大气模式中重力波参数化方案的重要条件之一,高垂直分辨率探空资料扰动场是获取重力波参数气候特征的基础数据;目前,获取扰动场的方法较多,但基于不同方法计算的扰动场对重力波参数气候特征影响的研究较少。基于2014—2017年山西太原气象台高垂直分辨率探空资料,利用2—4阶曲线拟合方法获取下平流层（17—24 km高度）温度扰动场、纬向风扰动场和经向风扰动场,经统计发现2阶与3阶曲线拟合方法的扰动场相似程度较高;在此选取相似度较高的2阶、3阶曲线拟合方法的扰动场分别计算大气重力波参数,并对大气重力波参数间的气候差异特征进行研究。结果表明:（1）不同阶曲线拟合方法扰动场的变化振幅及随高度变化趋势存在差异,且扰动场间的相关较弱;（2）2阶、3阶曲线拟合方法扰动场得到的重力波参数大小、年内变化趋势及在不同区间范围内占有率均存在差异,且相关较弱;（3）1—12月,相对3阶曲线拟合方法的扰动场,基于2阶曲线拟合方法的扰动场得到的重力波群速、水平波长、垂直波长、周期、固有相速均较大,而重力波能量上传百分比在某些月份较大。因此,不同阶曲线拟合方法扰动场间存在差异,会导致计算得到的大气重力波参数气候特征存在差异,最终对研制大气模式中的大气重力波参数化方案产生影响。   相似文献   

Editorial     

《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(1):1-2

The assessment of rock-fall hazards is subject to significant uncertainty, which is not fully considered in general practice and research. This paper reviews and classifies the various sources of the uncertainty. Taking a generic framework for risk assessment as source, a probabilistic model is presented that consistently combines the different types of uncertainties, in order to obtain a unified estimate of rock-fall risk. An important aspect of the model is that it allows for incorporating all available information, including physical and empirical models, observations and expert knowledge, by means of Bayesian updating. Detailed formulations are developed for various types of information. Finally, two examples considering rock-fall risk on roads, with and without protection structures, illustrate the application of the probabilistic modeling framework to practical problems.  相似文献   

Floods,drought, and seed mass of riparian plant species     

《Journal of Arid Environments》2013

Plant communities in dryland riparian ecosystems are influenced by flood disturbance and water availability. As global climate change alters stream flow regimes, there is increasing need to understand which traits allow plant species to persist under increased stress and disturbance. Small seed mass is part of a strategy that adapts for disturbance, but the role of seed mass as an adaptation for drought is less well documented. For dryland riparian plant communities, we asked, does seed mass vary with water availability and flood frequency? We compared community seed mass between sites that vary in flow permanence (longitudinal water gradient) and between hydrogeomorphic surfaces within sites (lateral gradients of moisture and disturbance). Using data from four rivers in Arizona, we contrasted seed mass between plant groups. We found community seed mass to be greater at sites with ephemeral than perennial flow, and to increase laterally from wet, frequently-flooded channel edges to dry, less disturbed terraces. Seed mass varied by moisture group (smallest for hydroriparian species) and by disturbance group (smallest for disturbance species), and showed a trend for being greater in introduced species. We conclude that small seed mass is independently associated with wet and disturbed conditions in dryland riparian ecosystems.  相似文献   

Using long-term datasets to study exotic plant invasions on rangelands in the western United States     

《Journal of Arid Environments》2013

Invasions by exotic species are generally described using a logistic growth curve divided into three phases: introduction, expansion and saturation. This model is constructed primarily from regional studies of plant invasions based on historical records and herbarium samples. The goal of this study is to compare invasion curves at the local scale to the logistic growth curve using long-term datasets. Five datasets ranging 41–86 years in length were recovered from five sites in four western states. Data for the following seven exotic species were analyzed using regression analysis to evaluate fit to a non-linear sigmoidal logistic curve: crested wheatgrass (Agropyron cristatum), dwarf alyssum (Alyssum desertorum), cheatgrass (Bromus tectorum), Lehmann lovegrass (Eragrostis lehmanniana), halogeton (Halogeton glomeratus), Russian thistle (Salsola tragus) and tumble mustard (Sisymbrium altissimum). A greater variety of curve shapes was documented by long-term datasets than those published based on herbaria sampling. Only two species from three different sites and with three different data types met the criteria for fitting a logistic curve. Many of the other species/location combinations were characterized by sporadic spikes and crashes. The general lack of fit with the model may be the results of the complex interactions that drive vegetation change in rangeland environments.  相似文献   

Hydrological shifts and tree growth responses to river modification along the Apalachicola River,Florida     

Matthew C. Smith  Justin T. Maxwell  Chris Van Dyke 《自然地理学》2013,34(6):491-511

Shifts in the hydrologic regime of Florida’s Apalachicola River have been attributed to anthropogenic changes throughout its watershed, including local dam construction. To assess impacts of those shifts on floodplain forests, we reconstructed tree growth using dendrochronology and compared these trends with hydrological and climatic variables. Comparisons of stream-gage data before and after dam construction on the Apalachicola River revealed statistically significant mean declines in annual average stage. Mean minimum annual stages, rise rates, and fall rates also decreased, while hydrograph reversals increased. Growth in four tree species correlated strongly with site-specific inundation parameters. A wetter climate in the two decades following dam construction and fine-scale fluctuation of the hydrograph may have set the stage for positive growth releases. Logging and hurricane wind throw events may have also contributed. However, drier conditions in the last two decades are now exacerbated by stage-discharge declines that had been masked previously. Tree growth rates and recruitment have decreased and, in the absence of a major disturbance, the forest canopy is composed of an older cohort of individuals. Our findings highlight how hydrograph variability, climate change, and vegetation disturbance are all relevant for gaging and anticipating the range of impacts of river modification on floodplain forests.  相似文献   

Exploring spatial data uncertainties in land‐use change scenarios     

N. Dendoncker  C. Schmit  M. Rounsevell 《International journal of geographical information science》2013,27(9):1013-1030

This paper evaluates errors and uncertainties in representing landscapes that arise from different data rasterization methods, spatial resolutions, and downscaled land‐use change (LUC) scenarios. A vector LU dataset for Luxembourg (minimum mapping unit: 0.15 ha; year 2000) was used as the baseline reference map. This map was rasterized at three spatial resolutions using three cell class assignment methods. The landscape composition and configuration of these maps were compared. Four alternative scenarios of future LUC were also generated for the three resolutions using existing LUC scenarios and a statistical downscaling method creating 37 maps of LUC for the year 2050. These maps were compared in terms of composition and spatial configuration using simple metrics of landscape fragmentation and an analysis of variance (ANOVA). Differences in landscape composition and configuration between the three cell class assignment methods and the three spatial resolutions were found to be at least as large as the differences between the LUC scenarios. This occurred in spite of the large LUC projected by the scenarios. This demonstrates the importance of the rasterization method and the level of aggregation as a contribution to uncertainty when developing future LUC scenarios and in analysing landscape structure in ecological studies.  相似文献   

Causal models as multiple working hypotheses about environmental processes   总被引：6，自引：0，他引：6  

Keith Beven 《Comptes Rendus Geoscience》2012,344(2):77-88

The environmental modeller faces a dilemma. Science often demands that more and more process representations are incorporated into models (particularly to avoid the possibility of making missing process errors in predicting future response). Testing the causal representations in environmental models (as multiple working hypotheses about the functioning of environmental systems) then depends on specifying boundary conditions and model parameters adequately. This will always be difficult in applications to a real system because of the heterogeneities, non-stationarities, complexities and epistemic uncertainties inherent in environmental prediction. Thus, it can be difficult to define the information content of a data set used in model evaluation and any consequent measures of belief or verisimilitude. A limit of acceptability approach to model evaluation is suggested as a way of testing models, implying that thought is required to define critical experiments that will allow models as hypotheses to be adequately differentiated.  相似文献   

EH4及地质雷达在隧道事故调查中的应用     

王鑫 《云南地质》2012,(1):84-88

引水隧道施工中屡次发生坍塌,用探地雷达对衬砌质量及地质情况进行探测。经数据反演,清晰勾画出衬砌背后空洞、松散堆积体分布范围,地下水的赋存特征,为治理事故提供切实可靠依据。  相似文献   

Behavioral responses of a harbor porpoise (Phocoena phocoena) to playbacks of broadband pile driving sounds     

《Marine environmental research》2013

The high under-water sound pressure levels (SPLs) produced during pile driving to build offshore wind turbines may affect harbor porpoises. To estimate the discomfort threshold of pile driving sounds, a porpoise in a quiet pool was exposed to playbacks (46 strikes/min) at five SPLs (6 dB steps: 130–154 dB re 1 μPa). The spectrum of the impulsive sound resembled the spectrum of pile driving sound at tens of kilometers from the pile driving location in shallow water such as that found in the North Sea. The animal's behavior during test and baseline periods was compared. At and above a received broadband SPL of 136 dB re 1 μPa [zero-peak sound pressure level: 151 dB re 1 μPa; t₉₀: 126 ms; sound exposure level of a single strike (SEL_ss): 127 dB re 1 μPa² s] the porpoise's respiration rate increased in response to the pile driving sounds. At higher levels, he also jumped out of the water more often. Wild porpoises are expected to move tens of kilometers away from offshore pile driving locations; response distances will vary with context, the sounds' source level, parameters influencing sound propagation, and background noise levels.  相似文献