Late pleistocene history of coniferous woodland in the mohave desert

Seventeen ancient wood-rat middens, ranging in radiocarbon age from 7400 to 19,500 years and to older than 40,000 years, have been uncovered in the northeastern, north-central, southeastern, and southwestern sectors of the Mohave Desert. Excellent preservation of macroscopic plant materials (including stems, buds, leaves, fruits, and seeds) enables identification of many plant species growing within the limited foraging range of the sedentary wood rat. An approximately synchronous zonal differentiation of vegetation in response to a gradient of elevation on limestone in the northeastern Mohave Desert is apparent from the macrofossil evidence, preserved in wood-rat middens and ground-sloth coprolites, covering a time span bracketed by radiocarbon ages of about 9000 and 10,000 years. XerophilQus juniper woodlands descended to an elevation of 1100 meters, some 600 meters below the present lower limit of woodland (1700 meters) in the latitude of Frenchman Flat. But desert or semidesert shrubs coexisted with the woodland trees throughout much of the span of elevation corresponding to the pluvial lowering of the woodland zone, and the more mesophytic phase of pinyonjuniper woodland was evidently confined to montane habitats at elevations above 1500 meters. Joshua trees, accompanied by desert shrubs, prevailed down to about 600 meters at Gypsum Cave, Nevada, but only the shrubs of the existing warm-desert vegetation occurred at 530 meters near Rampart Cave, Arizona. Pleistocene middens from the southeastern Mohave Desert record a relatively large downward shift of the pinyon-juniper woodland zone, paralleling the remarkably low minimum elevation of the existing woodland zone in that area. The macrofossil evidence speaks for former continuity of the many disjunct stands of woodland vegetation in the Mohave Desert region, at least along the higher divides connecting most of the ranges. However, there is no macrofossil evidence of pluvial continuity of range for the more mesophytic, montane, coniferous-forest zone of ponderosa pine or white fir now occupying islands of relatively mesic environment on the highest mountains of the region. On the contrary, the uneven stocking of the lofty mountains of the Mohave Desert with mesephytic or boreal species and the trend toward endemism suggest a long history of isolation.     

Coincidence of climatic and faunal fluctuations in pleistocene bermuda

As the climate of Pleistocene Bermuda oscillated during the last two glacial cycles, coincident variation occurred for a variety of independent events in the form and diversity of land snails. This variation was influenced primarily by the availability of calcium carbonate for shell construction.     

Late pleistocene faunal extinctions in southern patagonia

Major environmental changes recorded in pollen records from various sites in southern Patagonia and Tierra del Fuego are also reflected in pollen and cuticle data from dung of the late Pleistocene groundsloth. The most prominent change was the large-scale reduction of steppe environment about 10,000 years ago, which coincides with the latest dates for extinctions of many large grazers such as the giant groundsloth. Stress on food resources for all the large grazers may well have hastened their extinction. Hunting pressure by paleoindians may have been the final blow.     

Continental pleistocene climatic variations from speleothem age and isotopic data

Speleothems from continental North American caves have been dated by means of the (230)Th/(234)U method. Oxygen isotopic variations in the dated samples and phases of speleothem deposition can be interpreted in terms of climatic change. A glacial chronology constructed from the age and isotopic data lends support to the astronomical theory of climatic change.     

Glacial and pluvial periods: their relationship revealed by pleistocene sediments of the red sea and gulf of aden

Oxygen isotope analyses of planktonic foraminifera from the Red Sea and Gulf of Aden indicate that during periods of maximum continental and polar glaciation in the late Pleistocene, the Red Sea was subject to strong evaporation. Between glacial maximums the salinity of the Red Sea was equal to or below that of the open ocean. This suggests that high-latitude glacial periods corresponded in time to interpluvial stages in the present-day desert belt of northern Africa, whereas high-latitude interglacial periods coincided with pluvial stages.     

Late pleistocene paleotemperatures at tongue of the ocean, bahamas

Estimates of paleotemperatures, based upon paleoecological analysis of planktonic foraminiferal thanatocoenoses of three piston cores from Tongue of the Ocean, Bahamas, indicate a maximum mean variation between Late Pleistocene glacial and nonglacial stages of 3.6 degrees C. The data also indicate that the Early Wisconsin glacial stage was 0.7 degrees C warmer than the Late Wisconsin glacial stage.     

21世纪以来河南省植被覆盖变化及气候驱动解析

借助MODIS NDVI数据和气象插值数据,采用一元线性回归、Hurst指数及相关分析等方法,从年际尺度探讨河南省21世纪以来植被覆盖时空变化规律,并分析其对气候因素的响应特征。结果表明:河南省植被覆盖区域差异较大,NDVI频度呈单峰结构;近16年来,河南省大部分地区植被覆盖呈现增加趋势,10年平均增速约为4%(P0.01),且阶段性明显;河南省植被变化的同向特征强于反向特征,植被覆盖整体上呈持续改善态势,但郑州、洛阳、焦作等市域局部地区存在持续减小现象;年平均温度的上升是平原区植被覆盖增加的主要驱动因子,但升温尤其是年平均最高温度增加抑制了山区植被生长,植被覆盖对气候因子的敏感程度地域异质性明显。     

Tertiary climatic change in the marginal northeastern pacific ocean

Analysis of distributional patterns of shallow-water molluscan faunas of the middle latitudes of the marginal northeastern Pacific Ocean discloses a sharp reversal during the Miocene of the progressive climatic deterioration. A low point in the Tertiary cooling trend during the Oligocene was followed by climatic warming that culminated during the middle Miocene, as illustrated by a series of zoogeographic profiles.     

Late quaternary zonation of vegetation in the eastern grand canyon

Fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24,000 years in the eastern Grand Canyon. Past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones. A model emphasizing a latitudinal shift of climatic values is proposed.     

福建省植被气候生产力的时空分布特征

估算了福建省近30年来的植被气候生产力,结果表明,福建省植被气候生产力从东南部沿海向西北方向逐渐降低。全省植被气候生产力的高值区域主要集中在东南沿海部分,大部分县市在16000 kg.hm-2.a-1以上;西部和北部的山区植被气候生产力值较低,大部分在10000-15000 kg.hm-2.a-1之间。近30年来福建省植被气候生产力有逐渐提高的趋势,全省植被气候生产力以20世纪80年代最低,21世纪初期几年最高,相差1407 kg.hm-2.a-1。     

张承地区植被指数时空演变特征及其与气候因子的关系

为研究对张承地区生态环境质量改善具有重要现实意义的植被动态变化及其与气候影响因素间的关系,本研究解析张承地区2000—2014年气候因子与植被指数(NDVI)的时空演变特征,进而揭示该区域气候因子与植被指数的相关关系。结果表明:1)2000—2014年张承地区NDVI整体呈现增长趋势,年际波动较大,季节差异和空间分异特征显著。2)对于气候要素,15年间光合有效辐射与气温呈下降趋势,而年降水量呈现出增长趋势,且具有明显季节差异。3)在季节尺度上,夏季NDVI与降水量的相关性最显著,而在冬季NDVI与气温和光合有效辐射的相关性更显著;在年际尺度上,NDVI与光合有效辐射相关性较低,但却与降水量呈显著正相关,与气温呈显著负相关。4)不同植被类型的NDVI与气候因子的相关程度存在差异,但对于同一植被类型,NDVI与降水量的相关性最高。这些研究结论将为张承地区应对气候变化、改善生态环境提供重要参考信息。     

浙江杨梅主产地气候资源和气候变化特征

应用1961～2005年的逐日气候资料,运用数理统计方法和气候趋势系数法,分析浙江省19个观测站的年总辐射、年日照时数、年平均气温、年积温、年降水量等分布特征和变化趋势。结果表明浙江省杨梅主产地的温度偏高,雨量和光照适宜,气候条件利于杨梅栽培。从气候变化趋势来看,热量条件明显增加,降水表现为缓慢增多,而日照呈现为明显的下降趋势。因此,在杨梅栽培和引种时,要充分考虑气候变化影响,实现浙江杨梅产业持续发展。     

马雷绿洲植被覆盖度时空变化特征及与气候因子的关系

基于TM/ETM遥感数据和FCD模型植被覆盖度反演方法反演中亚地区马雷绿洲1988、2001和2010年植被覆盖度,分析了马雷绿洲1988—2010年植被覆盖度的空间格局和时空变化规律,并结合该区域同时期年均温度和年降水量数据,分别从不同空间和时间尺度上分析了植被覆盖度和气候变化的响应。结果表明:1)马雷绿洲面积呈扩大趋势,植被覆盖度由绿洲内部向外围递减,变化速率为0.12/10km,越趋近于绿洲边缘这种变化就越大;2)1988—2010年植被覆盖度总体呈上升趋势,1988—2001年增加尤为明显,平均为0.20/10年,2001—2010年趋于平缓,绿洲内部植被覆盖面积变化强烈、复杂及没有规律性,受人类活动影响较大,土地弃耕、撂荒现象十分严重;3)马雷绿洲植被覆盖度与降水和年均温度存在一定的相关性,与年降雨量、年均温度的平均相关系数分别为0.39和-0.33,其中绿洲内部植被覆盖度与年降水量和年均温度相关性较高,绿洲外围的荒漠地区相关性一般。     

Weather variability, climatic change, and grain production

A cooling trend in the world's climate would have serious effects in the monsoon belts depending on whether or not the recent changes in snow and ice cover in the polar regions were responsible for the droughts in Africa and the failure of the monsoons over South Asia. The cooling and shrinking of the atmosphere at the higher latitudes is believed to have brought the subtropical anticyclones nearer to the tropical rainbelt and have caused a shifting of the monsoon belt. The regions that would be most severely affected by a continuation of the cooling trend to the year 2000 would be the higher latitudes (above 50 degrees) where spring wheat is grown and the warm band below 30 degrees latitude where rice is the principal grain crop. Weather variability is a much more important consideration in grain production than a cooling trend. Our highest yields are made when weather is near normal or slightly cooler than normal. It is when weather variables deviate greatly from normal that yields are lowest. Even if the weather does trend toward the coolness of a century ago yields will not be reduced significantly unless the weather becomes more varible.     

黄土高原植被的时空变化及其驱动力分析研究

为研究气候变化及人类活动对植被的影响,本研究通过趋势分析探究黄土高原地区植被的时空变化,结合Hurst指数法以研究黄土高原植被的可持续性,采用相关分析和多元回归分析、残差分析等方法,探讨气候变化和人类活动对区域植被变化的影响。结果表明:1)黄土高原的植被在空间上由东南向西北呈现递减趋势,1982—2015年NDVI变化总体上呈弱上升趋势,2000年是NDVI时间序列的转折点,NDVI上升速度加快;2)Hurst指数表明研究区NDVI的未来变化趋势呈现持续性和反持续性的区域分别占13.70%和86.30%;3)相关分析和偏相关分析表明平均温度和降水对黄土高原NDVI均有显著影响,并且平均温度和降水对NDVI的综合影响更加明显;4)根据残差分析发现人类活动对植被的变化也有影响,改善和破坏作用并存。因此,1982—2015年黄土高原植被变化是气候变化和人类活动共同作用的结果,其中主要影响因素为人类活动,黄土高原地区气候因子对植被恢复的贡献率4.56%,非气象因子(人类活动)对植被恢复的贡献率为32.74%。     

内蒙古荒漠草原植被NPP时空变化及气候因子分析：以四子王旗为例

基于遥感数据和气象数据,利用光能利用率模型(CASA),对典型荒漠草原四子王旗1987—2016年植被NPP进行测算,分析NPP时空变化及其与年均气温和年降水量等气候因子的相关性。结果表明:1)1987—2016年四子王旗植被NPP值为144.52g/(m2·年)(C),植被类型地带性分布差异明显,空间上表现出南高北低的分布特征;2)1987—2016年四子王旗植被NPP总体呈现出增长趋势,年际波动为3.09～3.69Tg(C);3)研究区植被NPP与年均气温和年降水量呈显著正相关关系,且与年降水量相关系数更高,表明年降水量是影响荒漠草原区植被NPP的主要气候因子。通过研究荒漠草地植被NPP时空分布及其与气候因子的关系,有助于认识荒漠草原陆地生态系统对气候变化的响应。     

Historical nile floods and their implications for climatic change

Analysis of Nile flood stages from A.D. 640 to 1921 reveals major episodes of low Nile discharge during the years 930 to 1070 and 1180 to 1350 and major episodes of high Nile floods during 1070 to 1180 and 1350 to 1470. Examination of Nile flood maxima and minima and comparison with water levels in Lake Chad reveal a correlation between high Nile discharge and greater rainfall in equatorial East Africa. There is also apparently a correlation between low Nile discharge and cold climate in Europe.