BASIC FEATURES OF FOREST STEPPE IN THE LOESS PLATEAU OF CHINA

ＢＡＳＩＣＦＥＡＴＵＲＥＳＯＦＦＯＲＥＳＴＳＴＥＰＰＥＩＮＴＨＥＬＯＥＳＳＰＬＡＴＥＡＵＯＦＣＨＩＮＡ￥ＺｈｕＺｈｉｃｈｅｎｇ（朱志诚）（ＤｅｐａｒｔｍｅｎｔｏｆＢｉｏｌｏｇｙ．ＮｏｒｔｈｗｅｓｔＵｎｉｖｅｒｓｉｔｙ，Ｘｉａｎ７１００６９，ＰＲＣ）Ａ...     

CLIMATIC VARIATIONS IN CHINA OVER THE LAST 2000 YEARS

1 INTRODUCTIONIn the last years, evidence for climate changes showed that the timing of the two great climatic events of “Medieval Warm Period” (MWP) and “Little Ice Age” (LIA) differed geographically (HUGHES et al., 1994, JONES and BRADLEY, 1992). In other words, the cold or warm periods in one region were often not coincident with those in other regions. The Northern Hemisphere warmth degree in the Middle Ages was lower than or at most comparable to that in the mid-20…     

Spatio-temporal evolution of ecologically-sustainable land use in China's Loess Plateau and detection of its influencing factors

Ecological land(Eco-land) is a basic resource for human beings to survive, and eco-land use is a strategy, a way to manage the land resource. So, ecologically-sustainable land use is essential for human beings to survive. This paper investigates the spatiotemporal characteristics and mechanisms of urban-rural eco-land using a new and innovative integration way based on eco-land change data in China's Loess Plateau(LP) prefecture level cities and explores factors of eco-land change. The spatial difference characteristic of eco-land among different level cities in the LP is that: small cities big cities middle cities. From 2009 to 2016, the eco-land in the LP from the perspective of urban-rural areas has changed significantly. Significant differences of urban-rural eco-land were identified among various urban growth types, and all the cities in the LP were further classified into four types based on eco-land change trend, with type A and B cities identified as the vital zone and major zone. Taking the eco-fragile region Loess Plateau(LP) as an example, our results demonstrated that the migrants to cities in LP could relieve ecological pressures and promote restoration of ecological vegetation. We have demonstrated that urbanization and the influence of government policy can be discerned through the quantification of the spatial-temporal change of eco-land and suggest that combining both urban and rural eco-land can support more effective land use decisions and provide theoretical basis for the practical application of urban planning, policy-making and sustainable development. What's more, governments should strive to population mobility and restore vegetation to sustain this fragile ecological environment.     

SEDIMENT DISCHARGE OF THE HUANGHE RIVER AND ITS EFFECT ON SEDIMENTATION OF THE BOHAI SEA AND THE YELLOW SEA

The Huanghe (Yellow) River, with annual sediment discharge about 11 ×108tons, contributes about 17% of the fluvial sediment discharge of world's 21 major rivers to the ocean because its middle reaches flow across the great Loess Plateau of China. Sediment discharge of the Huanghe River has a widespread and profound effect on sedimentation of the sea. The remarkable shift of its outlet in 1128-1855 A.D. to the South Yellow Sea formed a large subaqueous delta and provided the substrate for an extensive submarine ridge field.The shift of its outlet in the modern delta every 10 years is the main reason why with an extremely heavy sediment input and a micro- tidal environment, the Huanghe River has not succeeded in building a birdfoot delta like the Mississippi. The Huanghe River has consistently brought heavy sediment input to sea at least since 0.7 myr.B.P. Paleochannels, paleosols, cheniers and fossils on the sea bottom indicate that the Yellow Sea was exposed during the late Quaternary glacial low-sea l     

STUDY ON THE SPATIAL PATTERNS OF LAND-USE CHANGE AND ANALYSES OF DRIVING FORCES IN NORTHEASTERN CHINA DURING 1990-2000

Land-use change is an important aspect of global environment change. It is, in a sense, the direct result of human activities influencing our physical environment. Supported by the dynamic serving system of national resources, including both the environment database and GIS technology, this paper analyzed the land-use change in northeastern China in the past ten years (1990–2000). It divides northeastern China into five land-use zones based on the dynamic degree (DD) of land-use: woodland/grassland — arable land conversion zone, dry land — paddy field conversion zone, urban expansion zone, interlocked zone of farming and pasturing, and reclamation and abandoned zone. In the past ten years, land-use change of northeastern China can be generalized as follows: increase of cropland area was obvious, paddy field and dry land increased by 74.9 and 276.0 thousand ha respectively; urban area expanded rapidly, area of town and rural residence increased by 76.8 thousand ha; area of forest and grassland decreased sharply with the amount of 1399.0 and 1521.3 thousand ha respectively; area of water body and unused land increased by 148.4 and 513.9 thousand ha respectively. Besides a comprehensive analysis of the spatial patterns of land use, this paper also discusses the driving forces in each land-use dynamic zones. The study shows that some key biophysical factors affect conspicuously the conversion of different land-use types. In this paper, the relationships between land-use conversion and DEM, accumulated temperature (⩾10°C) and precipitation were analysed and represented. We conclude that the land-use changes in northeast China resulted from the change of macro social and economic factors and local physical elements. Rapid population growth and management changes, in some sense, can explain the shaping of woodland/grassland — cropland conversion zone. The conversion from dry land to paddy field in the dry land — paddy field conversion zone, apart from the physical elements change promoting the expansion of paddy field, results from two reasons: one is that the implementation of market-economy in China has given farmers the right to decide what they plant and how they plant their crops, the other factor is originated partially from the change of dietary habit with the social and economic development. The conversion from paddy field to dry land is caused prmarily by the shortfall of irrigation water, which in turn is caused by poor water allocation management by local governments. The shaping of the reclamation and abandoned zone is partially due to the lack of environment protection consciousness among pioneer settlers. The reason for the conversion from grassland to cropland is the relatively higher profits of farming than that of pasturing in the interlocked zone of farming and pasturing. In northeastern China, the rapid expansion of built-up areas results from two factors: the first is its small number of towns; the second comes from the huge potential for expansion of existing towns and cities. It is noticeable that urban expansion in the northeastern China is characterized by gentle topographic relief and low population density. Physiognomy, transportation and economy exert great influences on the urban expansion. Foundation item: Under the auspices of Knowledge Innovation program Key Project of the Chinese Academy of Sciences (KZCX-2-308). Biography: LIU Ji-yuan (1947 - ), male, a native of Shanghai Municipality, professor, Director General of Institute of Geographical Sciences and Natural Resources Research, the Chinese Academy of Sciences. His research interests include environment and resources, remote sensing and geography.     

RECENT TRENDS OF TEMPERATURE AND PRECIPITATION DISTURBED BY LARGE-SCALE RECLAMATION IN THE SANGJIANG PLAIN OF CHINA

The regional observed temperature and precipitation changes and their abrupt jumps disturbed by large-scale reclamation in the Sanjiang Plain, Northeast China were studied. Mean annual temperature of the region was tending to go up and has increased by 1.2-2.2℃ over the past 50 years. A warming jump of mean annual temperature of the region occurred in the 1980s, which had an increase amplitude of 0.9℃. Linear tendency rates of annual precipitation were negative in most of the region. The maximum of annual precipitation decrease was 155.8mm over the past 50 years. An abrupt decrease of regional annual precipitation happened in the middle of the 1960s,which had a decrease of 102.1 mm. Based on the fact of climatic change of the Sanjiang plain over the past 50 years,it is held that the region had larger warming amplitude than that change of the Sanjiang Plain over the past 50 years,it is held that the region had larger warning amplitude than that of the surrounding areas in the recent years, which resulted from the large-scale reclamation of various kinds of wetlands.     

Red Clay Sediment in the Central Chinese Loess Plateau and Its Implication for the Uplift of the Tibetan Plateau

Introduction A set of reddish clay-silt-sized sediments named red clay underlying the Quaternary loess-paleosol sequence widely distribute in the Chinese Loess Plateau. The thickness of the red clay sediments ranges from decades of meters to over 100 m (Evan et al.1991,Mo and Derbyshire 1991, SUN et al. 1997&1998, DING et al. 1999, GUO et al. 2001, QIANG et al. 2001). Previous studies show that not only loess-paleosol (e.g.LIU et al.1985,AN et al.1990,DING et al.1992),but also red …     

Fossil pigments as indicators for palaeoclimatic interpretations —A case study of Qinghai Lake

An 82 cm core was collected from Qinghai Lake in the Qinghai-Xizang Plateau, China and sectioned in intervals of 1 cm for analysis of pigments (i. e. chlorophyll derivatives, carotenoids, myxoxanthophyll, oscillaxanthin) and²¹⁰Pb.²¹⁰Pb dating was used to establish the chronological sequence. The concentrations of myxoxanthophyll and oscillaxanthin from the cyanophytes increase with temperature. There are four peak values at 0–14 cm (present−1891a), 25 cm (1786a), 45 cm (1581a), 60 cm (1416a) representing four warm and low water level periods during the past 700 years. This was confirmed by the high concentration of carbonate and ∂¹³C in these stages. In these 700 years, there were also 4 periods of cold wet climate and high water level as indicated by the tree ring index and high value of native chlorophyll and high, variable CD/TC ratios. The project was supported by the Loess and Quaternary Research Lab, Academia Sinica.     

PREDICTION OF SEDIMENT REDUCING BENEFIT UNDER DIFFERENT RAINFALL CONDITIONS AND CONTROL DEGREES ON THE LOESS PLATEAU DEGREES ON THE LOESS PLATEAU

Soilerosionisoneofthemostseriousenvironmentalproblemsinthepresentworld.Itnotonlyrestrictstheproductionofagriculturebadly,butalsothreatensthenaturalenvironmentonwhichhumanbeinglive.Andthismakethemankindconfrontedwithtremendouschallenge.OntheLoessPlateau,soilandwaterlossisterrible,environmentisweak,anditshighsandyieldmakestheriverwayinthelowerreachesoftheHuanghe(Yellow)Riverfilledup,riverbeddrivenup,floodthreatprickedup,andresultsingreathiddentroublestothecontrollingoffloodandtherunningofirrig…     

Effect of altitude and latitude on surface air temperature across the Qinghai-Tibet Plateau

The correlation between mean surface air temperature and altitude is analyzed in this paper based on the annual and monthly mean surface air temperature data from 106 weather stations over the period 1961–2003 across the Qinghai-Tibet Plateau. The results show that temperature variations not only depend on altitude but also latitude, and there is a gradual decrease in temperature with the increasing altitude and latitude. The overall trend for the vertical temperature lapse rate for the whole plateau is approximately linear. Three methods, namely multivariate composite analysis, simple correlation and traditional stepwise regression, were applied to analyze these three correlations. The results assessed with the first method are well matched to those with the latter two methods. The apparent mean annual near-surface lapse rate is −4.8 °C /km and the latitudinal effect is −0.87 °C /^olatitude. In summer, the altitude influences the temperature variations more significantly with a July lapse rate of -4.3°C /km and the effect of latitude is only −0.28°C /^olatitude. In winter, the reverse happens. The temperature decrease is mainly due to the increase in latitude. The mean January lapse rate is −5.0°C /km, while the effect of latitude is −1.51°C /^olatitude. Comparative analysis for pairs of adjacent stations shows that at a small spatial scale the difference in altitude is the dominant factor affecting differences in mean annual near-surface air temperature, aided to some extent by differences of latitude. In contrast, the lapse rate in a small area is greater than the overall mean value for the Qinghai-Tibet Plateau (5 to 13°C /km). An increasing trend has been detected for the surface lapse rate with increases in altitude. The temperature difference has obvious seasonal variations, and the trends for the southern group of stations (south of 33° latitude) and for the more northerly group are opposite, mainly because of the differences in seasonal variation at low altitudes. For yearly changes, the temperature for high-altitude stations occurs earlier clearly. Temperature datasets at high altitude stations are well-correlated, and those in Nanjing were lagged for 1 year but less for contemporaneous correlations. The slope of linear trendline of temperature change for available years is clearly related to altitude, and the amplitude of temperature variation is enlarged by high altitude. The change effect in near-surface lapse rate at the varying altitude is approximately 1.0°C /km on the rate of warming over a hundred-year period.     

RECONSTRUCTING HOLOCENE PALAEORUNOFF REGIMES FROM PALAEOCLIMATE: AN INITIAL ATTEMPT TO APPLY A CLIMATOLOGICAL APPROACH TO PALAEOHYDROLOGY FOR THE NORTH CHINA PLAIN

１　ＩＮＴＲＯＤＵＣＴＩＯＮＲｕｎｏｆｆｉｓｄｅｆｉｎｅｄａｓｔｈｅｗａｔｅｒｔｈａｔｄｒａｉｎｓｆｒｏｍｔｈｅｌａｎｄｉｎｔｏｃｒｅｅｋｓａｎｄｒｉｖｅｒｓ（Ｌａｎｇｂｅｉｎｅｔａｌ．，１９４９）ａｎｄｔｈｕｓａｖｅｒｙｉｍｐｏｒｔａｎｔｈｙｄｒｏｌｏｇｉｃａｌｐａｒａｍｅｔｅｒｄｅｓｃｒｉｂｉｎｇｑｕａｎｔｉｔｙｓｔａｔｕｓｏｆｓｕｒｆａｃｅｗａｔｅｒ．Ｉｔｉｓｌａｒｇｅｌｙａｆｕｎｃｔｉｏｎｏｆｔｈｅｃｌｉｍａｔｉｃｃｏｎｄｉｔｉｏｎｓｔｈｏｕｇｈｉｔｉｓａｌｓｏａｆｆｅｃｔｅｄｂｙｖｅ…     

Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Loess Plateau Gully Region,China

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion.Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data(1981–2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation(SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997,respectively. Compared with that in the baseline period(1981–1996), annual runoff and annual sediment yield in the change period(1997–2012)decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff(137.9%) and annual sediment yield(135%) and were more important than precipitation. Biological measures(forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures(terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau.     

Ice-wedge Pseudomorphs Showing Climatic Change Since the Late Pleistocene in the Source Area of the Yellow River, Northeast Tibet

Introduction The Tibetan Plateau, located in west China, was uplifted during the Cenozoic and became the most youthful plateau in the world. Some researches have also shown that it started to develop into the cryosphere in the beginning of the Middle Pleistocene and became one of the three global cryospheres (two other cryospheres being the Artic and the Antarctic) (SHI et al. 1996). Because of the cryosphere development in the Tibetan Plateau, many periglacial and permafrost geomorpholog…     

A GIS-based modeling approach for fast assessment of soil erosion by water at regional scale,loess plateau of China

The objective of this study is to develop a unique modeling approach for fast assessment of massive soil erosion by water at a regional scale in the Loess Plateau, China. This approach relies on an understanding of both regional patterns of soil loss and its impact factors in the plateau area. Based on the regional characteristics of pre- cipitation, vegetation and land form, and with the use of Landsat TM and ground investigation data, the entire Loess Plateau was first divided into 3 380 Fundamental Asses...     

Sediment Delivery across Multiple Spatio-temporal Scales in an Agriculture Watershed of the Chinese Loess Plateau

There is a consensus that sediment delivery ratio in the Chinese Loess Plateau is close to 1at the inter-annual timescale. However, little information is available about the sediment delivery at finer timescales. We evaluated the sediment delivery from plots to watersheds at the event or intra-annual, annual, and inter-annual timescales within the Wudinghe river basin, a 30,261 km2 basin in the Loess Plateau. We calculated the ratio of sediment output to sediment input and presented the temporal change of the channel morphology to determine whether sediment deposition occurs.Although a single flood event frequently has a sediment yield exceeding 10,000 t km-2, sediment deposition rarely occurs except during some small runoff events(sediment yield 5000 t km-2) or dry years(sediment yield 10,000 t km-2) when moving from slopes up to the main channels of the Wudinghe River. This observation suggests a sediment delivery ratio close to 1 even at the event or intra-annual and the annual timescales, but not necessarily at the interannual timescale. Such a high sediment delivery ratio can be related to hyper-concentrated flows, which have very strong sediment transport capacity even at low flow strength. Because hyper-concentrated flows are well-developed in the whole Loess Plateau, a sediment delivery ratio close to 1 below the interannual timescale possibly remains true for other rivers in the Loess Plateau.     

近20年黄土高原土地利用/覆被变化特征分析

本文根据黄土高原地区20世纪80年代末、2000年、2008年3期土地利用/覆被空间数据集,计算2个时段（20世纪80年代末-2000年,2000-2008年）土地利用/覆被转类方向及其幅度、土地利用/覆被转类指数、土地利用/覆被状况指数及其变化率,分析黄土高原地区自20世纪80年代末以来土地利用/覆被时空变化特征以及宏观生态状况的变化趋势。结果显示：黄土高原地区近20年来平均土地利用/覆被状况指数为24.07,其中土石山区生态系统综合功能最好,其次为河谷平原区,最差的为农灌区。20世纪80年代末-2000年,黄土高原地区主要土地利用/覆被转类是森林和草地转为耕地,生态级别由高级向低级转移,2000-2008年主要土地利用/覆被转类是耕地转为林地和草地,低覆盖草地转为中高覆盖草地,生态级别由低级向高级转移。近20年来黄土高原地区地覆被状况指数变化以及土地利用/覆被转类指数表明,该区域的宏观生态状况总体上经历了转差（20世纪80年代末-2000年土地利用/覆被转类指数为-1.08）,后转好（2000-2008年土地利用/覆被转类指数为2.66）2个过程。这一变化过程前期受区域气候变化以及人口增长共同驱动,后期则叠加了生态工程的影响。     

近20年来黄土高原地区的经济增长时空分异特征

 经济不均衡增长是区域发展的一种常态。分析区域经济增长时空差异及成因,对于认识和加快落后地区的经济发展具有重要的意义。本研究在GIS技术的支持下,对黄土高原地区近20年来以县市为单元的经济增长时空分异特征进行了系统的分析。主要结论有:改革开放以来,黄土高原地区的GDP水平呈现出持续的快速增长态势。近20年来,陕北和内蒙古鄂尔多斯地区增长最为迅速;人均GDP的空间分布整体上呈现出"两高一低"的带状分布格局,且这种格局明显地受到极化增长的扰动和重塑;经济增长表现出显著的极化增长特征,且经济增长极的极化作用与增长极之间地位的调整是同时进行的;与常态化的城市产业集聚推动型经济相比,机遇性的资源开发拉动型经济对人均GDP的拉动速度更快,但可持续性较差。未来,黄土高原地区应走以中心城市带动为主,以能矿产资源开发拉动为辅,两者相互促进,共同带动整个区域经济更快、更好、更可持续地发展的道路。     

Decadal cimatic variations indicated by dulan tree-ring and comparison with other proxy data in China of the last 2000 years

Based on high-resolution tree-ring data from Dulan area of Qinghai Province, five spells have been divided: the warm period before 230’s A. D., the cold period between 240’s A. D. and 800’s A. D., the significantly warm period between 810’s A. D. and 1070’s, i. e. “Medieval Warm Period”, the cold period including the “Little Ice Age” 1420’ – 1870’s and the warming period since 1880’s. All the eleven coldest or warmest decades and several great abrupt changes took place before the Middle Ages, indicating that climatic system operated in great instability during the period 150’s – 1100’s A. D., Comparison of the tree-ring data with other temperature proxy data from East China, Guliya ice core as well as the south of Qinghai-Xizang Plateau shows that such great climatic events as Eastern Han warm period between the beginning of the 1st century and the previous fifty years of the third century, the cold period covering the span of the Wei, the Jin, and the Southern and Northern dynasties, the well-known “Medieval Warm Period” as well as the “Little Ice Age” appeared in these series such as East China and Dulan area. Only the first two climatic events were recorded conspicuously in Guliya ice core while the “Medieval Warm Period” and “Little Ice Age” is far weaker. Also, the well-defined “Medieval Warm Period” didn’t occurred in the south of Qinghai-Xizang Plateau. The warming since the 20th century is the warmest in the last 2000 years Guliya ice core, the second in Dulan area and East China, but it scarcely seems pronounced in the eastern part of Qinghai-Xizang Plateau. Foundation item: Under the auspices of the projects of the Chinese Academy of Sciences (KZ951-A1-204-02 and KZ951-A1 402-03). Biography: YANG Bao(1971–), male, a native of Yanggao County, Shanxi Province, Ph. D. His research interestinclude global change.     

Human settlement evaluation in mountain areas based on remote sensing, GIS and ecological niche modeling

The Qinghai-Tibet Plateau is the world’s highest and largest plateau. Due to increasing demands for environment exploration and tourism, a large transitional area is required for altitude adaptation. Hehuang valley, which locates in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau, has convenient transportation and relatively low elevation. Our question is whether the geographic conditions here are appropriate for adapted stay before going into the Qinghai-Tibet Plateau. Therefore, in this study, we examined the potential use of ecological niche modeling (ENM) for mapping current and potential distribution patterns of human settlements. We chose the Maximum Entropy Method (Maxent), an ENM which integrates climate, remote sensing and geographical data, to model distributions and assess land suitability for transition areas. After preprocessing and selection, the correlation between variables and spatial autocorrelation input data were removed and 106 occurrence points and 9 environmental layers were determined as the model inputs. The threshold-independent model performance was reasonable according to 10 times model running, with the area under the curve (AUC) values being 0.917 ± 0.01, and 0.923 ± 0.002 for test data. Cohen’s kappa coefficient of model performance was 0.848. Results showed that 82.22% of the study extent was not suitable for human settlement. Of the remaining areas, highly suitable areas accounted for 1.19%, moderately for 5.3% and marginally for 11.28%. These suitable areas totaled 418.79 km², and 86.25% of the sample data was identified in the different gradient of suitable area. The decisive environmental factors were slope and two climate variables: mean diurnal temperature range and temperature seasonality. Our model showed a good performance in mapping and assessing human settlements. This study provides the first predicted potential habitat distribution map for human settlement in Ledu County, which could also help in land use management.     

“Suspending village” a model of new development area in the ningxia hui autonomous region of China

The southern part of the Ningxia Hui Autonomous Region in China was infamous for its poverty and serious soil erosion caused by over population. In order to alleviate poverty and backwardness, a plan was worked out: to remove 200,000 people to the north plain by developing newly irrigated land during the period of 1983–1992. The plan has been in operation for eight and half years to date. About 200,000 people have been removed from the poor southern part to the newly developed area, and 800,000 mu (1/ 15 ha) of desert land has been cultivated. Most of the migrants have been lifted out of poverty and the people ’s life in the south is being improved. During the immigration process, a model, called “Suspending Village”, has been developed. In the article, the whole process of the development and the strategies are discussed.