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1.
The desert and sandy land are the products of arid climate. The spatial distribution of modern deserts and sandy land in China and their relation to climate show following characteristics: arid and hyper-arid desert zones, at isohyet of less than 200 mm, are dominated by mobile dunes; semi-arid steppe and arid desert steppe with the precipitation between 200-400mm, are dominated by semi-fixed and fixed sand dunes; the precipitation of sub-humid forest grassland and humid forest zones with scattered fixed sand land is higher than 400 mm. With this as reference, in combination with considerable amount of paleoclimatic data in desert regions and adjacent regions, the distributions of desert and sandy land in China during the last interglacial period, the last glacial maximum (LGM), and the Holocene megathermal, were preliminarily reconstructed. The results compared with that of today show that the distribution of desert and sandy land in China was greatly dwindled during last interglacial period, and the mobile dune area was about two-thirds of that of today's, but greatly expanded during LGM. However, the dwindling area of desert and sandy land in the Holocene megathermal was smaller than that in the last interglacial period. The forcing mechanism was mainly related to the changes of East Asian winter and summer monsoon, south-northward swing of the westerlies and the variations of the Qinghai-Tibet Plateau monsoon intensity caused by global climate changes during the cold and warm intervals since the last interglacial period.  相似文献   

2.
The desert and sandy land are the products of arid climate. The spatial distribution of modern deserts and sandy land in China and their relation to climate show following characteristics: arid and hyper-arid desert zones, at isohyet of less than 200 mm, are dominated by mobile dunes; semi-arid steppe and arid desert steppe with the precipitation between 200–400 mm, are dominated by semi-fixed and fixed sand dunes; the precipitation of sub-humid forest grassland and humid forest zones with scattered fixed sand land is higher than 400 mm. With this as reference, in combination with considerable amount of paleoclimatic data in desert regions and adjacent regions, the distributions of desert and sandy land in China during the last interglacial period, the last glacial maximum (LGM), and the Holocene megathermal, were preliminarily reconstructed. The results compared with that of today show that the distribution of desert and sandy land in China was greatly dwindled during last interglacial period, and the mobile dune area was about two-thirds of that of today’s, but greatly expanded during LGM. However, the dwindling area of desert and sandy land in the Holocene megathermal was smaller than that in the last interglacial period. The forcing mechanism was mainly related to the changes of East Asian winter and summer monsoon, south-northward swing of the westerlies and the variations of the Qinghai-Tibet Plateau monsoon intensity caused by global climate changes during the cold and warm intervals since the last interglacial period.  相似文献   

3.
The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal. yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age. Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194)  相似文献   

4.
During the late Pleistocene, a number of climatic fluctuations such as the Heinrich events were recorded in the climatic proxies in the Loess Plateau and in North China[1―7]. Most of these records were based on geophysical and geochemical evidence[1―4]. Therefore, more biologic evidence is necessary for explaining the regional ecosystems in response to climatic change in the Loess Plateau during this period since pollen re-cords in other areas presented strong evidence to cli-matic fluctu…  相似文献   

5.
Normalized Difference Vegetation Index (NDVI) is widely recognized as a good indicator of vegetation productivity. Diagnosing the NDVI trend and understanding climatic factors influences on NDVI can predict the productivity changes under different climatic scenarios. This paper examined NDVI dynamic and its response to climate factors during a 10 year period (1998–2008) in Inner Mongolia. The main findings are as follows: (1) The NDVI multi-scale characters can be revealed well by wavelet transform, and the average NDVI and the NDVI amplitude show a gradually decreased trend from northeast to southwest in Inner Mongolia during the past 10 years, furthermore, this trend is consistent with the heat and water distribution caused by latitude difference in north–south direction and Asia monsoon effect in east–west direction. (2) The relation between NDVI and temperature is the most close, followed by precipitation, sunshine hours and relative humidity. Different vegetation cover types show different strengths in correlation between NDVI and climate variables with the correlation values decreasing from forest, meadow steppe to desert steppe in whole. (3) The precipitation and temperature have the same change cycle, both nearly 290 days in the 20 selected stations. The NDVI has the same change cycle with the precipitation and temperature or either 10 days earlier or later than precipitation and temperature, which supports the significant correlation between NDVI and its climatic factors from a new perspective. The nearly 290 days change cycle implies that the vegetation growth cycle is nearly 10 months and there are no obvious differences change cycles in different vegetations. (4) Vegetation dynamic is significantly correlated to the temperature and precipitation at the time scale of 10, 20, 40, 80, 160, and 320-day, respectively, and the S3 scale (i.e., the time scale of 80-day), nearly 3 months (one season), is most significant and suitable for evaluating the vegetation dynamic to climatic factors.  相似文献   

6.
This study focuses on how irrigation processes affect local climate over arid areas. The chosen study area is northwest China, a typical arid region where three dominant land‐use types are irrigated cropland, grassland, and desert. Observational analysis indicates that the highest precipitation, the coolest surface temperatures, and the slowest warming trend are seen over irrigated cropland from 1979 to 2005. The single column atmospheric model (SCAM), developed by the National Center for Atmospheric Research (NCAR), was used to investigate and better understand the differences in long‐term climate conditions and change over the above three land‐use types. The results indicate that local climate conditions are predominantly controlled by large‐scale forcing in this arid region and that local land surface forcing related to vegetation cover change and irrigation processes also has a significant impact. This study strongly suggests that a realistic climate forecast for this region can be achieved only with both accurate large‐scale and local climate forcing. The irrigated cropland of the region generates stronger evaporation that cools the surface and slows the warming trend more than does the evaporation from the natural grassland and desert. Stronger evaporation also significantly increases precipitation, potentially alleviating the stress of irrigation demands in arid regions. A series of sensitivity SCAM simulations indicate that a drier and warmer climate occurs with decreasing vegetation cover in the irrigated cropland region. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981–2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981–1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990–1998; (3) vegetation cover declined rapidly during 1999–2001; and (4) vegetation cover increased rapidly during 2002–2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology. Supported by the National Natural Science Foundation of China (Grant No. 40671019) and the Knowledge Innovation Project of the Institute of Geographical Sciences and Natural Resources Research of Chinese Academy of Sciences  相似文献   

8.
Changes in the vegetation and climate of the westerly-dominated areas in Central Asia during the Holocene were interpreted using pollen-assemblages and charcoal data from a 300-cm-long sediment core of the Sayram Lake,northern Xinjiang.Accele-rator Mass Spectrometry(AMS) radiocarbon dating methods were applied to bulk organic matter of the samples.Artemisia spp./Chenopodiaceae ratios and results from principal component analysis were used to infer that the lake basin was dominated by desert vegetation before ca.9.6 cal.ka BP,which suggests a warm and dry climate in the early Holocene.Desert steppe/steppe expanded during 9.6-5.5 cal.ka BP,indicating a remarkable increase both in the precipitation and temperature during the mid-Holocene.Desert vegetation dominated between 6.5 and 5.5 cal.ka BP,marking an extreme warmer and drier interval.The steppe/meadow steppe recovered,and temperatures decreased from 5.5 cal.ka BP in the late Holocene,as indicated by the increased abundance of Artemisia and the development of meadows.Holocene temperatures and moisture variations in the Sayram Lake areas were similar to those of adjacent areas.This consistency implies that solar radiation was the main driving factor for regional temperature changes,and that the effect of temperature variations was significant on regional changes in humidity.The evolution of climate and environment in the Sayram Lake areas,which were characterized as dry in the early Holocene and relatively humid in the middle-late Holocene,are clearly different from those in monsoonal areas.Dry conditions in the early Holocene in the Sayram Lake areas were closely related to decreased water vapor advection.These conditions were a result of reduced westerly wind speeds and less evaporation upstream,which in turn were caused by seasonal changes in solar radiation superimposed by strong evaporation following warming and drying local climate.  相似文献   

9.
One of the goals for paleaoenvironmental research is to predict the tendency of future climate and environmental changes based on the understanding of the past. The key approach is to find similar pictures which happened in the past. By understanding the background and mechanism of the paleaoenvironmen- tal changes, reliable parameters and verifications can be provided for the numerical model to predict the tendency of future climate and environmental changes. The Mid-Holocene as the nearest …  相似文献   

10.
Pollen-based reconstruction of vegetation patterns of China in mid-Holocene   总被引：1，自引：0，他引：1  
Biomization provides an important way to assign pollen taxa to biomes and to simulate palaeo-vegetation patterns, so that pollen data can be mapped to reconstruct biogeography and climate. The authors have tested the applicability of this procedure to assign modern pollen surface samples from China to biomes. The procedure successfully delineated the major vegetation types of China. When the same procedure was applied to 6 ka B. P. fossil pollen samples, the reconstructions showed that the forest zones were systematically shifted northwards ca. 300–500 km beyond their present northern limits in eastern China; the area of desert and steppe vegetation was reduced compared to the present in northwestern China; the area of tundra was reduced largely on the Tibetan Plateau. This research is a contribution to the project of BIOME 6000 in Pacific-Asian regions. Project supported by the Funding for Returned Students from the Overseas of the State Education Commission of China, the Postdoctoral Station, and State Pilot Laboratory of Coast & Island Development of Nanjing University, Financial support has also been provided by European Community (EV5V-CT95-0075) and by the Swedish Natural Science Research Council (G-AA/GU 09334-321).  相似文献   

11.
Investigating the spatial and temporal variance in productivity along natural precipitation gradients is one of the most efficient approaches to improve understanding of how ecosystems respond to climate change. In this paper, by using the natural precipitation gradient of the Inner Mongolian Plateau from east to west determined by relatively long-term observations, we analyzed the temporal and spatial dynamics of aboveground net primary productivity (ANPP) of the temperate grasslands covering this region. Across this grassland transect, ANPP increased exponentially with the increase of mean annual precipitation (MAP) (ANPP=24.47e0.005MAP, R2=0.48). Values for the three vegetation types desert steppe, typical steppe, and meadow steppe were: 60.86 gm-2a-1, 167.14 gm-2a-1 and 288.73 gm-2a-1 respectively. By contrast, temperature had negative effects on ANPP. The moisture index (K ), which takes into ac- count both precipitation and temperature could explain the spatial variance of ANPP better than MAP alone (ANPP=2020.34K1.24, R2=0.57). Temporally, we found that the inter-annual variation in ANPP (cal- culated as the coefficient of variation, CV) got greater with the increase of aridity. However, this trend was not correlated with the inter-annual variation of precipitation. For all of the three vegetation types, ANPP had greater inter-annual variation than annual precipitation (PPT). Their difference (ANPP CV/PPT CV) was greatest in desert steppe and least in meadow steppe. Our results suggest that in more arid regions, grasslands not only have lower productivity, but also higher inter-annual variation of production. Climate change may have significant effects on the productivity through changes in precipitation pattern, vegetation growth potential, and species diversity.  相似文献   

12.
L&#;  Houyuan  Wang  Sumin  Wu  Naiqin  Tong  Guobang  Yang  Xiangdong  Sheng  Caiming  Li  Shijie  Zhu  Liping  Wang  Luo 《中国科学:地球科学(英文版)》2001,44(1):292-300

A new pollen record from the lake of Co Ngoin in the central Tibetan Plateau provides information on the vegetation and climate changes during the last 2.8 Ma. Seven major significant changes in pollen associations indicate the processes of vegetation change and possible tectonic uplifts. The seven changes in vegetation succession include a temperate montane conifer and broad-leaved mixed forest, cold temperate montane dark conifer forest, alpine shrub-meadow and alpine desert, montane dark coniferous forest and alpine shrub meadow, montane dark coniferous forest and alpine shrub meadow, montane dark coniferous forest and alpine meadow, and alpine desert and meadow. The pollen record provides the evidence of at least five times tectonic uplifts occurring at about 2.58 Ma, 1.87 Ma, 1.17 Ma, 0.83 Ma, and 0.3 Ma ago, respectively. Before 0.8 Ma, this region maintained the altitude below 4000 m a.s.l. Larger amplitude of uplift occurring at about 0.8 Ma ago enforced the plateau rising into cryosphere, shaping the basic topographic pattern of modern plateau. The major successions in vegetation of this area were largely controlled by stepwise uplift of the Tibetan Plateau.

  相似文献   

13.
Knowledge of long-term change in vegetation and climate in semi-arid/arid regions is essential for the study of current climate and development of mitigation strategies against severe drought. Here, a fossil pollen record of annually-varved core from Sugan Lake in interior Qaidam Basin was quantitatively analyzed to reconstruct changes in vegetation, floristic diversity and drought frequency. Results of biomization suggested that regional vegetation was desert vegetation with three short-term occupations of temperate steppe/xerophytic shrub during the last 2700 years. Floristic diversity generally increased/decreased with the expansion/degradation of desert vegetation. Moisture fluctuations showed three distinct stages(extremely dry between 742 BC and ~AD500, relatively wet with an increasing trend between ~AD500 and 1200 and relatively wet with frequent fluctuations after AD1200), interrupted by 14 drought events. Spectral analysis and continuous wavelet transform of moisture variation revealed 200-and 120-year cycles. According to cross-wavelet transform analysis, major drought frequency of ~200-year was explicitly correlated to solar activity. It's suggested that the centennial-scale drought frequency was mainly driven by solar activity, through modulation of large-scale atmospheric circulation. Furthermore, the effect of surface temperature–evaporation and uplifting/subsiding air flow should be notable. The climatic drought in interior Qaidam Basin could be intensified under the continuous global warming.  相似文献   

14.
The history of natural fire since 37 kaBP and its relationship to climate for the northern part of the South China Sea are revealed from the statistic study of charcoal particles and associated pollen data from deep sea core 17940 (20° 07’N, 117° 23’E, 1 727 m in water depth). Our study indicates that, during the last glaciation, the concentration of charcoal and the ratio of con centration between charcoal and terrestrial pollen are much higher than that of the Holocene. This can be explained as the relatively high strength and frequency of natural fire during glaciation which is probably due to the drier climate; during the Last Glacial Maximum (LGM), the substantial rising of the concentration of large and medium charcoal particles probably suggests the local source area of the natural fires, i.e. the exposed continental shelf; moreover, the correlation between charcoal concentration with different size and pollen percentage may elucidate different transport dynamics. During the glacial time, almost all the peak concentrations of small particles correspond with the peak pollen percentage ofArtemisia, an indicator of comparatively dry climate, while for large particles, their concentrations always lag behind small particles and thus change with pollen percentage of montane conifers implying relatively cold and humid climate. So, it is possible to assume that small particles reflect regional emissions under drier climate and were brought over by strengthened winter monsoon. When the climate became relatively humid, the increasing precipitation carried the large particles accumulated on continental shelf before under arid condition to the studied area.  相似文献   

15.
Modern pollen analysis is the basis for revealing the palaeovegetation and palaeoclimate changes from fossil pollen spectra. Many studies pertaining to the modern pollen assemblages on the Tibetan Plateau have been conducted, but little attention has been paid to pollen assemblages of surface lake sediments. In this study, modern pollen assemblages of surface lake sediments from 34 lakes in the steppe and desert zones of the Tibetan Plateau are investigated and results indicate that the two vegetation zones are dominated by non-arboreal pollen taxa and show distinctive characteristics. The pollen assemblages from the desert zone contain substantially high relative abundance of Chenopodiaceae while those from the steppe zone are dominated by Cyperaceae. Pollen ratios show great potential in terms of separating different vegetation zones and to indicate climate changes on the Tibetan Plateau. The Artemisia/Chenopodiaceae ratio and arboreal/non-arboreal pollen ratio could be used as proxies for winter precipitation. Artemisia/Cyperaceae ratio and the sum of relative abundance of xerophilous elements increase with enhanced warming and aridity. When considering the vegetation coverage around the lakes, hierarchical cluster analysis suggests that the studied sites can be divided into four clusters: meadow, steppe, desert-steppe, and desert. The pollen-based vegetation classification models are established using a random forest algorithm. The random forest model can effectively separate the modern pollen assemblages of the steppe zone from those of the desert zone on the Tibetan Plateau. The model for distinguishing the four vegetation clusters shows a weaker but still valid classifying power. It is expected that the random forest model can provide a powerful tool to reconstruct the palaeovegetation succession on the Tibetan Plateau when more pollen data from surface lake sediments are included.  相似文献   

16.
Influence of variation of soil spatial heterogeneity on vegetation restoration   总被引：23，自引：0，他引：23  
Ecological restoration as a new research field of applied ecology can be traced back to the 1950s, it mainly focuses on the studies of ecological restoration of mine fields, tropical forests, wetlands and indus-try-polluted ecosystems[1-4]. Following the raising of the conception of “restoration ecology”[5], the holding of a series of international conferences and the found-ing of the International Association for Restoration Ecology, the studies of ecological restoration has be-come a quit…  相似文献   

17.
Palynological records were selected from the profiles of three research sites in the mountainous interior of southern China(Dajiuhu at Shennongjia in the western part of Hubei Province, Dahu in the Nanling Mountains, and Gantang in the northern part of Fujian Province). It can be inferred that the forest vegetation growing in the south of the Qinling Mountains-Huaihe River was luxuriant during the late glaciation. The species succession with ecological significance in palaeoflora(Abies sp., Fagus sp. and Alnus sp.) revealed that there was a certain amount of precipitation and effective humidity in the mountain lands between Qinling Mountains-Huaihe River and Nanling Mountains. This ecological environment favored the zonal distribution of mountainous forest vegetation. The late glacial maximum featured a cold, wet climate that completely differed from the cold-dry climate on the Loess Plateau, and on the steppe and desert steppe of the Qinghai-Tibet Plateau. Besides being influenced by the predominant factors driving the Northern Hemisphere climate, the cold-wet climate feature of the mountainous interior of southern China was closely associated with some geographical factors such as the latitudinal position, proximity to the ocean, and the topography and landforms.  相似文献   

18.
Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.  相似文献   

19.
The arbuscular mycorrhizal (AM) fungal status of the 20 most common plant species distributed in 4 vegetation types (meadow steppe, desert steppe, steppe desert and typical desert) on the northern slopes of the Tianshan Mountains was investigated. Samples of the plant species and their rhizosphere soils were collected from the 4 vegetation zones and examined to compare their mycorrhizal status, AM fungal spore densities, biovolumes, and community structures. 28 AM fungal species were isolated from the rhizosphere soils: of these, 5 belonged to Acaulospora, 1 to Archaeospora and 22 to Glomus. 5 AM fungi, Glomus aggregatum, G. claroideum, G. deserticola, G. etunicatum and G. sinuosum, were observed in all 4 zonal types. No significant differences were observed in mean proportion of root length colonized by AM fungi among the plant species within each zonal type. Comparing the 4 zonal types, Plantago minuta (84.5%) in steppe desert and Eremopyrum orientale (83.1%) in typical desert showed the highest root colonizatsion rates. AM fungal spore densities and biovolumes were significantly different in the different zonal types. AM fungal spore densities and biovolumes, species richness and diversity were highest in meadow steppe and lowest in typical desert.  相似文献   

20.
内蒙呼包盆地晚更新世孢粉组合及其意义   总被引：7，自引：0，他引：7       下载免费PDF全文
窦素芹  麦学舜 《地震地质》1990,12(3):283-290
本文是对内蒙呼包盆地内二级台地沉积物进行孢粉分析的总结。根据对孢粉资料的分析研究得出,该区二级台地沉积物堆积时期的古植被是由森林草原过渡到荒漠草原,气候由湿凉转向干冷。通过孢粉组合的对比,证明二级台地形成于晚更新世晚期,相当于萨拉乌苏组的地层时代  相似文献   

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