Late pleistocene vegetation and degree of pluvial climatic change in the chihuahuan desert

Eight Pleistocene wood rat middens at elevations of 1200, 880, and 600 meters in the Chihuahuan Desert contain abundant macrofossils of pinyon pine, juniper, shrubby liveoak, and Opuntia, together with smaller quantities of Agave lecheguilla and other xerophytes of existing desert vegetation, which in dicate a xerophilous woodland vegetation in the lowlands, as much as 800 meters below existing woodland, during the Wisconsin pluvial. Ten radiocarbon dates show ages that range from 11,560 to 14,800 and 16,250 to 20,000 years, and to more than 40,000 years. Absence of most mesophytic montane species in deposits as high as 1200 meters indicates a lack of equivalent downward dis placement for the ponderosa pine zone or other zones of montane vegetation. Uneven stocking of isolated peaks in the Chihuahuan Desert province with montane species suggests that long-distance transport of propagules, rather than former continuity, may account for the disjunct distributions of many species.     

Development of vegetation and climate in the southwestern United States

Plant macrofossils in ancient packrat middens document the presence of woodland communities in most of the present Chihuahuan, Sonoran, and Mohave deserts in the southwestern United States during the late Wisconsinan (22,000 to 11,000 years before present by radiocarbon dating). Warm desert species were common in the woodlands at lower elevations and mixed conifer and subalpine forests were present at high elevations. Inferred mild, wet winters and cool summers produced unusual plant and animal associations compared to those of today. Montane communities acquired modern aspects and more mesophytic species disappeared from lower woodlands about 11,000 years ago. Early Holocene xeric woodlands and an inferred winter precipitation regime persisted until about 8000 years ago. The present circulation patterns, rainfall regimes, and biotic distributions probably formed as a result of the melting of the continental ice sheets. Southwestern communities appear to have responded quickly to climatic changes compared to the gradual responses of central and eastern United States forest communities.     

Holocene woodlands in the southwestern deserts

Twenty-nine radiocarbon-dated pack rat middens document woodland communities in the deserts of the southwestern United States less than 10,000 years ago. A synchronous change from woodland to desert or grassland occurred about 8000 years ago in the Chihuahuan, Sonoran, and Mohave deserts. A shift of the Aleutian low and the winter storm track to the north, which resulted in drastically reduced winter precipitation in these areas, is inferred. The shift to nonpluvial climates in the Southwest lagged behind the beginning of nonglacial climates in the North because the melting continental glaciers contined to affect general circulation patterns.     

A 22,000-Year Record of Monsoonal Precipitation from Northern Chile's Atacama Desert

Fossil rodent middens and wetland deposits from the central Atacama Desert (22 degrees to 24 degrees S) indicate increasing summer precipitation, grass cover, and groundwater levels from 16.2 to 10.5 calendar kiloyears before present (ky B.P.). Higher elevation shrubs and summer-flowering grasses expanded downslope across what is now the edge of Absolute Desert, a broad expanse now largely devoid of rainfall and vegetation. Paradoxically, this pluvial period coincided with the summer insolation minimum and reduced adiabatic heating over the central Andes. Summer precipitation over the central Andes and central Atacama may depend on remote teleconnections between seasonal insolation forcing in both hemispheres, the Asian monsoon, and Pacific sea surface temperature gradients. A less pronounced episode of higher groundwater levels in the central Atacama from 8 to 3 ky B.P. conflicts with an extreme lowstand of Lake Titicaca, indicating either different climatic forcing or different response times and sensitivities to climatic change.     

Late Tertiary Microflora from the Basin and Range Province,Arizona

Sediments of probable Clarendonian age from central Arizona have furnished the only late Tertiary pollen assemblage known from the Southwest. The associated trees, shrubs, and herbs resemble the chaparral and conifer-oak woodland communities of the semiarid foothills and mountains of central and southeastern Arizona, and suggest a late Tertiary landscape and climate for central Arizona similar to that of today.     

Cation-ratio and accelerator radiocarbon dating of rock varnish on mojave artifacts and landforms

The first accelerator radiocarbon dates of rock varnishes are reported along with potassium/argon ages of lava flows and conventional radiocarbon dates of pluvial lake shorelines, in an empirical calibration of rock varnish K(+) + Ca(2+)/Ti(4+) ratios with age in the Mojave Desert, eastern California. This calibration was used to determine the cation-ratio dates of 167 artifacts. Although cation-ratio dating is an experimental method, some dates suggest human occupation of the Mojave Desert in the late Pleistocene.     

基于地形因子的大都市边缘区土地利用变化分析——以北京市平谷区为例

为探讨平谷区在不同高程、坡度和坡向分级的土地利用变化规律,为土地资源可持续利用和管理决策提供依据,以北京市平谷区为例,借助DEM提取地形信息,对平谷区土地利用变化在各地形因子分级的分布特征进行分析,结果表明:1)平谷区的土地利用类型以耕地、园地和林地为主,1993-2008年的15年间,平谷区耕地面积大幅度减少,园地、居民点及工矿和交通用地面积明显增加;2)平谷区的土地利用变化在不同高程、坡度和坡向分级差异明显.耕地、居民点及工矿用地、交通用地的转化主要发生在0～300m高程带和小于15°的坡度带,林地与草地的互转主要发生在高程300～800m、坡度大于8°的阳坡与半阳坡;园地与草地的转化主要发生在高程0～300m、坡度在2～25°的半阳坡;园地与林地的转化主要发生在高程0～800m、坡度2～25°的阳坡与半阳坡,高程大于800m、坡度大于25°的区域主要是林地向其他地类的转化;3)平谷区的土地利用变化剧烈且与高程、坡度和坡向具有高度相关性,低高程和低坡度区域内主要表现为建设用地和园地增加以及耕地流失.随着高程、坡度增大,土地利用变化逐渐减弱.     

兴隆山自然保护区土壤的形成与分布

本文研究了由前震旦系和震旦系岩层构成的兴隆山土壤的形成和分布。结果表明:土壤形成及分布与气候、植被和海拔有显著的相互关系。随着海拔高度由2300米到3500米,温度由暖变寒,湿度由干燥到湿润,植被由落叶阔叶林(在2300米～2600米海拔范围)到以阔叶林为主的针阔混交林(2600米～3000米),再过渡到亚高山(3000米～3500米)和高山(>3500米)灌丛草甸,土体淋溶由弱变强,3000米以上土壤风化变成寒冻风化为主,相应的土壤类型依次由石灰性灰褐土和典型灰褐土到淋溶灰褐土,渐变到亚高山灌丛草甸土,到高山草甸土和高山灌丛草甸土,其中淋溶灰褐土面积最大。丰富的兴隆山土壤资源和它们相应的地理要素一起共同构成了黄土高原西部独特的生态环境。     

福建海岸山地5种优势树种叶形态特征对海拔资源位的响应

对灵石山次生林的2种优势乔木和3种优势灌木的比叶面积差异及其不同海拔资源位的变化规律进行分析。结果表明,米槠[Castanopsis carlesii(Hemsl.)Hayata.]与猴欢喜(Sloanea sinensis)2种乔木的比叶面积总体呈现随海拔升高而降低的趋势;围涎树(Irenina pithecollobii)、罗伞树(Ardisia quinquegona)和九节木(Psychotria rubra)3种灌木的比叶面积也出现随海拔升高而降低的趋势,但不明显;不同海拔资源位的2种优势乔木和3种优势灌木比叶面积之间具有显著差异;不同海拔资源位的同种乔木比叶面积具有显著差异;不同海拔资源位的灌木优势树种间的比叶面积也具有显著差异。因此,可以认为福建东南海岸带山地环境下植物对较小的环境变化都会产生明显的叶形态特征响应。     

福建省红黄壤利用改良区划要点

根据红黄壤利用改良区划的原则与分级标准,把福建省划分为两个土壤地带、四个地区和八个土区,即:Ⅰ中亚热带红壤黄壤地带Ⅰ_1武夷山-戴云山-鹫峰山山地红壤、黄壤、水稻土,林、粮、茶地区。Ⅰ_1(1)闽东北中山山地红壤、黄壤、黄泥田,改低、防蚀区。Ⅰ_1(2)闽西北中山山地黄壤、红壤、冷浸田,改低、培肥区。Ⅰ_1(3)闽北低山山间盆地红壤、冷浸田、潮泥田,改低、培肥、防蚀区。Ⅰ_1(4)闽中中山红壤、山地黄壤、黄泥田,综合治理区。Ⅰ_1(5)闽西南中山河谷盆地红壤、山地黄壤、紫色土、黄泥田,改低水土保持区。Ⅰ_2闽浙东部滨海丘陵平原红壤、水稻土、盐土,粮、茶地区。Ⅰ_2(1)闽东滨海丘陵平原红壤、乌泥田、黄泥田、埭田,防旱、培肥、水土保持区。Ⅱ南亚热带砖红壤性红壤和红壤地带Ⅱ_1东南沿海砖红壤性红壤、红壤、水稻土,粮、经作、热作地区。Ⅱ_1(1)闽东南滨海丘陵平原砖红壤性红壤、乌泥田、埭田、赤砂土,水土保持、培肥、防旱区。Ⅱ_2闽粤低山丘陵砖红壤性红壤、红壤、水稻土,粮、林、经作地区。Ⅱ_2(1)闽东南低山丘陵砖红壤性红壤、红壤、赤砂土、潮泥砂田,防湿、防旱区。     

The age of the Taklimakan Desert

The Taklimakan Desert is located in the foreland basin of the Tibetan Plateau. We report here the results of stratigraphic investigations of a 1626-meter-thick sequence with interbedded wind-blown silt from the southern marginal Taklimakan Desert. Because the studied section is located downwind of the desert, the eolian silt accumulation is closely linked to desert formation. Our new evidence indicates that shifting sand dunes prevailed in the Tarim Basin by at least 5.3 million years ago, as they do today. We attribute this event to late Cenozoic climatic deterioration, as well as to changes in atmospheric circulation induced by Tibetan Plateau uplift.     

Holocene vegetation in chaco canyon, new Mexico

Well-preserved plant remains in packrat middens chronicle vegetation change in Chaco Canyon over the past 11,000 years. Early Holocene evidence of communities dominated by Douglas fir, Rocky Mountain juniper, and limber pine in the San Juan Basin calls for revision of traditional constructs based on fossil pollen. Middle and late Holocene vegetation in the canyon was pinyon-juniper woodland up until Anasazi occupation between 1000 and 800 years ago. Instead of climate, Anasazi fuel needs may explain the drastic reduction of pinyon and juniper after 1230 years ago. The lack of pinyon-juniper recovery over the past millennium has implications for contemporary forest and range ecology.     

毛乌素沙地与植被有关的地下水环境研究

[目的]研究毛乌素沙地与植被有关的地下水环境。[方法]选择毛乌素沙漠腹地,研究沙漠地区植被与地下水的关系,建立了沙漠地区的研究植被与地下水关系的指标体系,即植被的种群、地下水埋深、包气带含水率、地下水矿化度和包气带含盐量等,以及相应的野外工作方法。[结果]结果表明,研究区分布有9个主要的植被种群,沙蒿（Artemisia）、沙柳（Salixpsammophila）和苔草（Carex）是优势植被;地下水矿化度在沙丘地区为100～300mg/L,滩地为800mg/L左右;包气带含水率全年维持在8%～16%;沙丘含盐量小于0.2%,滩地含盐量大于0.3%。[结论]这些成果为研究该区植被与地下水的关系提供了依据。     

基于马尔柯夫过程的干旱区景观生态环境动态分析——以新疆乌苏绿洲为例

[目的]采用1990年、2000年及2005年三期TM、ETM遥感影像为主要数据源,以新疆乌苏绿洲(乌苏-奎屯-独山子地区)为例,基于Markov过程原理,在景观尺度下分析该区域的生态环境动态过程与发展趋势,以期为关注干旱区生态环境动态变化,合理规划区域资源环境空间,促进绿洲可持续发展提供科学依据.[方法]研究以景观生态学理论和方法为指导,借助3S技术和图形处理软件.[结果]乌苏绿洲的区域景观生态环境动态变化主要表现为高山冰川退化、林草耕地化、土地盐渍化、低盖度草地荒漠化以及绿洲内林草地人居化;在空间动态上,农业发展主要为乌苏地区的奎屯河流域,城镇及工业化集中体现在奎屯、独山子地区,荒漠化、盐渍化主要发生在绿洲边缘地带,绿洲及其荒漠交错带的变化最为强烈.在发展趋势上,未来短期内绿洲一荒漠交错带面积减少,绿洲、荒漠的面积继续增大,但各景观类型的优势度并不会发生明显的变化,各景观类型仍然能够维持平衡.[结论]由于绿洲-荒漠交错带在荒漠绿洲平衡与共存机制中具有重要缓冲协调作用,一定程度上降低了生态环境压力,然而随着荒漠过渡带的减少,绿洲将面临更多新的生态问题,这在干旱区应受到应有重视.     

西藏东南部林牧交错带林地与湿地的土壤动物群落比较

比较研究西藏东南部典型林牧交错地带林地与湿地的土壤动物群落特征,为西藏东南部林地、湿地土壤动物群落研究提供科学数据。采用土钻法随机取样,Tullgren干漏斗法分离,参考土壤动物检索图鉴及大类别分类方法进行鉴定,并以DG多样性、Jaccard相似性系数q和Gower系数Sg分析该地区林地和湿地的土壤动物群落结构。结果表明,样地内(林地和湿地)共捕获土壤动物393头,属3门6纲18类,其中林地优势类群为弹尾目,湿地优势类群为弹尾目与前气门亚目。2种生态类型土壤动物群落的DG差异不显著,群落类群个体数相似性不高,但林牧交错地带林地与湿地土壤动物个体数的异质性比类群数高。西藏东南部林地与湿地土壤动物密度、类群以及群落多样性均不同。土壤含水量明显影响土壤动物群落结构与数量,土壤动物群落结构的类群与总个体数相似性均不高。     

黑河流域下游绿洲-荒漠梯度上的植被数量特征

根据野外样方调查,以实际测量区域内各物种植株的多种指标为依据,分析黑河下游乌兰图格断面中植被的盖度、重要值（P_i）沿垂直于河道方向的梯度分布规律。结果表明：在垂直于河道方向上,乌兰图格断面植被总盖度呈现先增加后减小的趋势,并根据盖度值划分出1 200 m以内为河岸绿洲区、2 200~3 700 m为荒漠过渡区、4 300 m以外为荒漠区;从重要值（P_i）上观察乔、灌、草的分布规律,发现绿洲区近河道处胡杨占据生存优势,一定距离后草本占优势;荒漠过渡区和荒漠区灌木占据生存优势。同时分析乌兰图格断面植被盖度与土壤平均质量含水量的关系发现,在荒漠过渡区和荒漠区,两者具有一定的相关性。选取土壤水分、植被盖度分别为自变量和因变量,建构回归模型,利用SPSS软件进行分析,发现两者间的关系可用回归方程很好地反映出来。     

塔克拉玛干沙漠及其周边山区水汽时空分布特征

利用沙漠腹地地基GPS数据、周边探空资料、MODIS近红外水汽数据,分别对塔克拉玛干沙漠的水汽进行初步分析,以期了解该区域的大气可降水量的时空分布特征。通过对塔克拉玛干沙漠及周边山区大气可降水量结果的分析可知,塔克拉玛干沙漠为西北地区大气可降水量的相对高值区,水汽值普遍高于其周边山区;沙漠西南部靠近青藏高原一带为水汽的低值区。无论是塔克拉玛干沙漠还是周边山区,大气可降水量的年内变化都是一致的,夏季最大,秋季高于春季,冬季大气可降水量最低。     

乌鲁木齐市周边荒山植物群落类型及其物种多样性

采用典型样地法对新疆乌鲁木齐市周边雅玛里克山、乌拉泊群山、焦化山、骑马山和雪莲山的自然植被类型及其物种多样性进行了研究。结果表明，研究区自然植被总体可划分为荒漠、灌丛、草原、草甸、沼泽、落叶阔叶林6大植被型组。植物群落类型有19种；其中荒漠、灌丛、草原植被的Shannon-wiener指数(H)为(0．92002～2．51113)，与温带植被相比，相对较低，反映了荒山植被不稳定性和所处生态环境的严酷性。均匀度高的植物群落．其多样性指数也越高，群落也越稳定。不同荒山的小蓬(Nanophyton Prinaceum)单优势荒漠的盖度越大，其重要值往往也大。但其均匀度和Shannon-wiener指数(H)却小。     

生物土壤结皮对荒漠土壤线虫群落的影响

在干旱的沙漠生态系统中,生物土壤结皮对于沙丘的固定和土壤生物的维持起着相当重要的作用.土壤线虫能敏感的指示土壤的恢复程度,是衡量沙区生态恢复与健康的重要生物学属性,而目前关于生物土壤结皮与土壤线虫的关系研究很少.为探明生物土壤结皮对土壤线虫的影响,以腾格里沙漠东南缘的人工植被固沙区藻结皮和藓类结皮覆盖的沙丘土壤为研究对象,根据固沙年限的不同将样地分为4个不同的区进行采样(1956、1964、1981和1991年固沙区),以流沙区作为对照;同时,在不同季度(4、7、9和12月)分别采集腾格里沙漠东南缘的人工植被固沙区藻结皮和藓类结皮覆盖下不同土层(0-10、10-20和20-30 cm)的沙丘土壤,以沙坡头地区的红卫天然植被区为对照,分析生物土壤结皮下土壤线虫的时空变化.采用改良的Baermann漏斗法进行分离线虫,用光学显微镜鉴定并统计.研究表明:1956、1964、1981和1991年人工植被固沙区的藻结皮和藓类结皮均可显著提高其下土壤线虫多度、属的丰富度、Shannon-Weaver多样性指数、富集指数和结构指数(P＜0.05),这可能是因为生物土壤结皮的存在为土壤线虫提供了重要的食物来源和适宜的生存环境;固沙年限与结皮下土壤线虫多度、属的丰富度、Shannon-Weaver多样性指数、富集指数和结构指数存在显著的正相关关系(P＜0.05),这说明固沙年限越久,越有利于土壤线虫的生存和繁衍;结皮类型显著影响土壤线虫群落,相对于藻结皮而言,藓类结皮下土壤线虫多度与属的丰富度更高(P＜0.05),这说明演替后期的藓类结皮比演替早期的藻结皮更有利于土壤线虫的生存和繁衍.此外,藻结皮和藓类结皮均可显著增加其下0-10、10-20和20-30 cm土层线虫多度和属的丰富度(P＜0.05),但随着土壤深度的增加,这种影响逐渐减弱,表明生物土壤结皮更有利于表层土壤线虫的生存;而且,随着季节的变化,藻结皮和藓类结皮下土壤线虫多度基本表现为秋季＞夏季＞春季＞冬季,这些反映了生物土壤结皮的生物量、盖度和种类组成随着季节变化而变化.因此,腾格里沙漠东南缘的人工植被固沙区生物土壤结皮的存在与演替有利于土壤线虫的生存和繁衍,增加了线虫数量、种类和多样性,这指示了生物土壤结皮有利于该区土壤及其相应生态系统的恢复.     

乌兰布和沙漠固沙树种病原真菌区系研究

乌兰布和沙漠固沙树木病原真菌可分为两种类型，即荒漠和半荒漠型，荒漠型的代表属有Ｌｅｖｅｉｌｌｕｌａ，半荒漠型的代表属有Ｍｅｌａｍｐｓｏｒａ。探讨了乌兰布和沙漠固沙树种病原菌区系特点。