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Table of Content

    25 January 2003, Volume 58 Issue 1 Previous Issue    Next Issue
    Some Key Issues Concerning Development of Geographical Science in China
    LU Dadao
    2003, 58 (1):  3-8.  doi: 10.11821/xb200301001
    Abstract ( )   PDF (785KB) ( )   Save

    In the past 20 years, outstanding progress has been made in the development of China's geographical science which consists of both applied aspect and talents training. It also played an essential role in the nation's major research projects. There were more than 200,000 people engaging in geographical education and research in institutions, universities and colleges as well as middle schools in China in 2002. There were 565 professors and 1,001 associate professors working in the major 42 geographical institutions, of which 8 have the power to confer Ph.D degree of primary disciplines and 65 to confer Ph.D degree of secondary disciplines. In the 42 institutions, there are 340 doctoral tutors. Since the second half of 1999, 586 PhD students and 1,579 master students have graduated. Some 1,006 PhD students and 2,563 master students were enrolled in the academic year of 2001-2002. Since 1999, the following projects have been managed: one national major project, and 20 key projects under the National Natural Science Foundation of China; 8 for National 863 Program; 6 special topics and 13 projects for National Brainstorm Program; 4 projects and 8 subjects for National 973 Program; foundation items for outstanding youth and 16 excellent research groups supported by foundations; one major knowledge innovation project and 7 key projects of CAS. In spite of the achievements mentioned above, certain fields in geographical research also face challenges and opportunities. In light with the existing problems, this paper discusses the development direction of the geographical sciences in the 21st century and puts forward suggestions on strengthening theoretical research and integrated research of geography.

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    Education of Geography in China: Inheriting and Innovation
    SHI Peijun, SONG Changqing, GE Daokai, FU Bojie, WANG Min,LIU Baoyuan, WANG Yanglin
    2003, 58 (1):  9-16.  doi: 10.11821/xb200301002
    Abstract ( )   PDF (1110KB) ( )   Save

    The education of geography should meet the needs of geographical talents in the science of earth system and sustainable development as well as the socio-economic development in China, especially meet the needs of sustainable development strategy. Therefore, it is necessary to launch a comprehensive reform about the primary and advanced education of geography. Three countermeasures to achieve development with leaps and bounds in geographical education are further presented in this paper: (1) in the background of earth system science and sustainable development science, to establish a new system of geographical education in China; (2) on the premise of adaptation to national and international criterion, to standardize the classification of geographical knowledge system and geographical curriculum system; and (3) on the premise of technical glossary censor, to normalize the terms of geographical advanced education.

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    Digital Simulation of Population Density in China
    LIU Jiyuan, YUE Tianxiang, WANG Ying'an, QIU Dongsheng, LIU Mingliang, DENG Xiangzheng, YANG Xiaohuan, HUANG Yujie
    2003, 58 (1):  17-24.  doi: 10.11821/xb200301003
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    Spatial distribution of population density is simulated on the basis of fusing remotely sensed data, meteorological data, soil data and statistical data by means of a grid-generation based model that is newly constructed in this paper. The result shows that the highest values of simulated population density almost centralized in the triangle-zone, taking Beijing, Shanghai and Zhengzhou city as its vertexes, and in the Pearl River Delta. In the meantime, the highest density triangle-zone tends to be a pentagon taking Shanghai-Nanjing- Hangzhou urban agglomeration, Wuhan city, Xi'an city, Beijing-Tianjin-Tangshan urban agglomeration and Shenyang-Dalian urban agglomeration as its five vertexes. The highest density zone in the Pearl River Delta is expanding to its outer-ring.

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    GIS Based Spatialization of Population Census Data in Qinghai-Tibet Plateau
    LIAO Shunbao, SUN Jiulin
    2003, 58 (1):  25-33.  doi: 10.11821/xb200301004
    Abstract ( )   PDF (1101KB) ( )   Save

    In the Qinghai-Tibet Plateau, correlation ratios between population density and percentages of arable land and city and town used land at county level reach 0.90 and 0.85 respectively. In Qinghai province, there exists a logarithmic correlation of ratio = -0.86 between population density and average territorial elevation at county level. There is a correlation of ratio = 0.82 between population density and main highway density at county level. Correlation ratios between population density and densities of city and town residential areas, township residential areas and village residential areas reach 0.82, 0.87 and 0.92 respectively. Density of residential areas drops along with increasing of distance to rivers. Therefore, territorial elevation, land use, road and river system are the main factors affecting distribution of population in the Qinghai-Tibet Plateau. Residential areas are an important indicator to distribution of population. Weight values of affecting factors are assigned objectively and multiple sources data fusion technology is applied to spatialize population census data. There is a correlation of ratio > 0.80 between the population density generated by data fusion and actual population at county level, and ratio > 0.75 at township level. The finally generated grid population density not only keeps consistence with statistical population data at county level but also reflects changes of population distribution inside each county.

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    Main Effect of Plateau Traffic on Land Use and Landscape Pattern Change: From Lanzhou to Golmud
    YAN Jianzhong, ZHANG Yili, LIU Linshan, SHEN Zhenxi, LIU Yanhua, ZHENG Du
    2003, 58 (1):  34-44.  doi: 10.11821/xb200301005
    Abstract ( )   PDF (1420KB) ( )   Save

    Based on digital land use data from 1995 to 2000, the land use and landscape pattern changes of Lanzhou-Xining route and Qinghai-Xizang route are studied on a macro-scale. The conclusions are given as follows: (1) Land use and landscape pattern along the Lanzhou-Xining Railway have not changed notably, while which along the Qinghai-Xizang Railway has changed remarkably. The land use pattern of the Qinghai-Xizang Railway and the Qinghai-Xizang Highway is just in the quick-change stage, so land use change will be fast in the future and built-up land will increase quickly. (2) The comprehensive degree of dynamic land use in the buffer zones of the Lanzhou-Xining Railway and the Qinghai-Xizang Railway shared the same trend, embodying the corridor effect of trunk line upon land use change. The prominent influence range of the Lanzhou-Xining Railway is 5 km, while which of the Qinghai-Xizang is 7 km. (3) The expanding range of city was mainly confined to a 1-km buffer, only Lanzhou showing its expanding range in a 3-km buffer zone.

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    Quantifying Land Use and Land Cover Change in Xilin River Basin Using Multi-temporal Landsat TM/ETM Sensor Data
    CHEN Siqing, LIU Jiyuan, ZHUANG Dafang, XIAO Xiangming,
    2003, 58 (1):  45-52.  doi: 10.11821/xb200301006
    Abstract ( )   PDF (1223KB) ( )   Save

    The land use/land cover change of Xilin River Basin in the past two decades was investigated through land use/cover classification of four sets of Landsat TM/ETM images acquired on July 31, 1987, August 11, 1991, September 27, 1997 and May 23, 2000, respectively. Primarily, 15 sub-classes land cover types were recognized, including 9 grassland types at community level: F. Sibiricum steppe, S. baicalensis steppe, A. chinensis + forbs steppe, A. chinensis + bunchgrass steppe, A. chinensis + Ar. frigida steppe, S. grandis + A. chinensis steppe, S. grandis + bunchgrass steppe, S. krylavii steppe, Ar. frigida steppe and 6 non-grassland types: cropland, urban area, wetland, desertified land, saline-alkaline land,and waterbody. To make the time series land cover classification data applicable for land use/cover change quantification analysis, the cloud, waterbody and cloud shadow features were extracted from each of the raw land cover maps and overlaid as a subset map. Then the area corresponding to the subset in each land cover classification map was eliminated. After this procedure, each of the final land cover classification map of Xilin River Basin was optimized and ready for land use/ cover change detection. The main characteristics of land use/land cover change in Xilin River Basin over the past two decades were a significant decrease in area of meadow grassland, temperate grassland vs. significant increase in area of cropland, desert grassland, urban area and desertified land. From 1987 to 2000, the area of both F. sibiricum meadow steppe and S. bacalensis meadow steppe decreased steadily year by year, whose net decrease was 525.5 km2 and 201.5 km2. While the area of S. krylavii desert steppe and Ar. frigida desert steppe increased year by year, whose net increases were 1,282.7 km2 and 1,045.6 km2 respectively. The desert grassland had the greatest increase in area, i.e., 2,328 km2, equal to 56% of the total area of desert grassland in 1987. The cropland and urban area increased from 114.3 km2 and 25.2 km2 in 1987 to 332.1 km2 and 43.6 km2 in 2000, respectively. The A. lymus + bunchgrass steppe, A. lymus + forbs steppe had the greatest decrease in area, i.e., 2,040 km2. During the four periods, A. chinensis + forbs steppe was the widest distributed land cover type in 1987 and 1991, with its area was 5281.2 km2 and 4104.3 km2, respectively. However, in 1997 and 2000, S. krylavii was the most widespread land cover type with an area of 4,109.6 km2 and 4,479.1 km2.

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    Simulation of Hydrological Response to Land Cover Changes in the Suomo Basin
    DENG Huiping, LI Xiubin, CHEN Junfeng, ZHANG Ming, WAN Hongtao
    2003, 58 (1):  53-62.  doi: 10.11821/xb200301007
    Abstract ( )   PDF (1089KB) ( )   Save

    In order to study the effects of land cover changes on hydrology, the TOPMODEL was tested for the Suomo basin on the upper reaches of the Yangtze River. A modified version of the model was used to adapt to the basin condition and data availability. The model was calibrated with five year measured daily discharge record (1980-1984) and the parameters were estimated. With this model and the maps of land cover of the 1970s, the 1980s and the 1990s, daily discharge from 1960 to 1999 was simulated. Comparing simulated discharge with the measured records from 1960 to 1999 in percentage efficiency, the model gave a sound result. After that, simulation was conducted under four land cover scenarios with the tested model. The main results were as follows: With the increase in land cover and interception capability, the basin interception evaporation increased, transpiration and soil evaporation decreased, and overall evaporation increased. Soil moisture increased and saturation zone storage and basin water storage decreased with the increase in land cover and maximum interception capability. Surface runoff and stream discharge decreased and subsurface runoff increased with the increase in land cover at the beginning while decreased with further land cover increase. The degree of hydrological effects of land cover increase depends on the difference value between actual evapotranspiration and potential evaporation.The bigger difference, the higher effects of land cover changes on basin hydrology are.

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    Process of Land Use/ Land Cover Change in the Oasis of Arid Region
    LUO Geping, ZHOU Chenghu, CHEN Xi
    2003, 58 (1):  63-72.  doi: 10.11821/xb200301008
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    Using remote sensing imagery data of 1978, 1987 and 1998, and taking the typical oasis in alluvial-diluvial/fan-alluvial-plain type in Sangong River Watershed as study area, the process and trend of oasis LUCC are analyzed by applying the methods of remote sensing (RS), geographic information system (GIS) and statistics. The main results of oasis LUCC in Sangong River Watershed are as follows.(1) RS and GIS are powerful techniques and methods in capturing oasis LUCC data and analyzing its spatial change.(2) Establishing mathematical models in the range, speed, regional differences and trend index of LUCC, especially the model of LUCC trend and state, the process and trend of oasis LUCC can be deeply studied, including bi-direction process, single-direction process, positive and negative process, rising and falling trend, etc. these models are applied to oasis of Sangong River Watershed and satisfactory effects have been obtained. (3) The LUCC in oasis has had a slow tendency since 1978 and obviously shows temporal and spatial differences. In the period of 1978-1987, the index of oasis LUCC trend and state was 0.58, which indicates that oasis LUCC presented non-equilibrium state with the transition process in single direction and evident regional differences: the state of LUCC was quasi-balanced in the upper part of oasis, but non-balanced in the middle and lower parts of oasis. In the period of 1987-1998, the index of oasis LUCC trend and state was 0.3, which indicates that the state of oasis LUCC was quasi-balanced with the transition process in bi-direction and showed the different regional changes compared with the period during 1987-1998: the state of LUCC was non-balanced in the upper and middle parts of oasis, but balanced in the lower part of oasis. (4) No matter how quantitative change or spatial change, the speed of LUCC in the middle part of oasis is the biggest among its parts and more than that of LUCC of entire oasis; the next is the lower part and the smallest is the upper part, whose speeds are all less than that of LUCC of entire oasis.

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    The Relationship of the Yellow River Flood and the Land Use in the Middle Reaches during the Han Dynasties
    WANG Shangyi
    2003, 58 (1):  73-82.  doi: 10.11821/xb200301009
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    According to the re-analysis on historical materials and combined with the modern scientific achievements on hydrology, physiognomy and soil erosion, the author puts forth the new viewpoint on the environmental influence resulting from the floods which occurred in the lower reaches and the land use styles in the middle reaches of the Yellow River. (1) Recordation in Hou Han Shu about most of the floods is simple and brief but it is more detailed about Yilo river floods. The river flooded several times then and one of those even emerged some places of the Luoyang city. If the trunk stream of the Yellow River was flooded in, flooding might also occur in the lower reaches. (2) During the 58 years from the river bursting in 11 AD till Wang Jing taming the River in 69 AD, there had been neither dam burst due to channel blockage nor harnessing practices in the lower reaches. Flood deluged arbitrarily. It is obvious that there was no record in detail on flood because of omission on purpose or with on intention. (3) Investigate the record about the flood in the Eastern Han Dynasty one year after another, the author found the frequency of flood in the Eastern Han Dynasty is higher than that in the Western Han Dynasty as well as the situation of the disaster. Wang Jing's river harnessment made the lower reaches stable for 36 years rather than what was previously considered as 800 or 83 years. (4) The population engaged in farming was reduced by more than 3/4 around the middle reaches of the Yellow River in the Eastern Han Dynasty. And a great deal of nomadic tribes immigrated in at that time, and their way of life by substantial damaging natural vegetation led to the aggravation of flood disaster of the lower Yellow River.

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    The Temperature Variations over the Antarctic Coastal Regions in the Past 250 Years
    ZHANG Mingjun, XIAO Cunde, LI Zhongqin, REN Jiawen, QIN Dahe, KANG Jiancheng, LI Jun
    2003, 58 (1):  83-89.  doi: 10.11821/xb200301010
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    By comparing the oxygen isotope temperatures recorded by 17 shallow ice cores from the coastal regions of Antarctica, this paper presents the special characteristics of the temperature variations over the Antarctic coastal regions in the past 50, 150 and 250 years. In the past 50 years, the isotopic temperatures recorded in the ice cores at different sites of the Antarctic coastal regions differ great. For instance, although the increasing isotopic temperatures have been reported for many sites studied, some sites show decreasing trends. In the past 150 years, the isotope temperatures in the coastal regions of Antarctica show an alternant-distributing pattern. In the past 250 years, all the ice cores from the coastal regions of Antarctica record the so-called Little Ice Age (LIA).

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    Dating the 1000-year-old Qilian Juniper in Mountains along the Eastern Margin of the Qaidam Basin
    SHAO Xuemei,, FANG Xiuqi,, LIU Hongbin, HUANG Lei
    2003, 58 (1):  90-100.  doi: 10.11821/xb200301011
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    In this paper, the methods for developing the master chronologies for 1000-year-old Qilian Juniper (Sabina przewalskii Kom.) are introduced in detail. Since the studied sites are located in the arid region of northeast Qinghai-Xizang Plateau, the tree-ring cores sampled contain a certain number of missing rings and several false rings. To assure the proper placement in time of each growth layer for the 1000-year-old trees, some improvements were made in the practice of master chronologic development. Firstly, trees with a variety of ages were sampled besides very old trees. The large sample depth benefited the identification of missing rings for cores from old trees and avoided the possibility that all collected specimens could be missing a ring for any one year. Secondly, cores from younger trees and from trees that exhibit a little width variation were selected to do the skeleton plot first and cores with many missing rings were done last when the ring-width pattern was known. Thirdly, inferring where rings may be missing was made based on the agreement among the narrow rings as well as among the wide rings. If the agreement of wide rings is not so good and there were some missing rings, the chronology from nearby sites was used to infer the year of missing ring occurrence. Finally, several methods, such as the computer program COFECHA and the line plots were used to examine the dating and the measurements of ring width for a site. The number of cores without missing rings and time span covered by them were also inspected to avoid the possibility that all collected specimens were added a missing ring for any one year. The Gleichlaufigkeit statistics was used to examine the dating agreement between master chronologies of different sites.

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    Landscape and Phenology of the Upper Reaches of the Luanhe River in the Yuan Dynasty
    CUI Haiting, WANG Wenjiang
    2003, 58 (1):  101-108.  doi: 10.11821/xb200301012
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    Historical information of landscape and phenology can be applied to reconstruction of ancient environment. In this paper we try to collect information of landscape and phenology from poems and articles of the Yuan Dynasty, and also use them to reconstruct the natural landscape in the upper reaches of the Luanhe River and its adjacent area. As above mentioned, data could be analyzed by using the method of physical geography and ecology. The authors suggest that there are five types of landscapes: (1) deciduous broad-leaved forest landscape in the western section of the Yanshan Mountains; (2) meadow steppe landscape in the edge and eastern part of the Inner Mongolia Plateau; (3) typical steppe landscape in the Zhangbei Plateau; (4) sparse forest steppe landscape in Hunshandake sandy land; and (5) wetland landscape on the lake shore and riverside. In addition, according to the comparison of plant phenology, the authors consider that the florescence was about 10 days earlier than the contemporary age in summer during the 1330s, and the first snow came about 10 days earlier than the contemporary age in winter during the mid-14th century.

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    Plant Communities and Their Interrelations with Environmental Factors in the Middle Reaches of the Tarim River
    ZHANG Yuanming, ZHANG Daoyuan, CHEN Yaning
    2003, 58 (1):  109-118.  doi: 10.11821/xb200301013
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    Plant communities were sampled in the lower reaches of the Tarim River, Xinjiang. The results showed that among the 475 sampled quartets from 19 sites, 23 plant species were identified, which belong to 21 genera in 11 families, most of which have low occurrence frequency in quadrats. The most common species of this study, Tamarix ramosissima occurred in 17 sites (89.47% of the total investigated sites), followed by Phragmites communis, which occurred in 12 sites (63.15% of the total investigated sites). Populus euphratica and Lycium ruthenicum were found in 11 sites respectively, accounting for 57.89% of the total sites. Quantitative classification (TWINSPAN) and ordination (CCA) methods were used to study the distribution patterns of 23 plant species at 19 sites in this study area. The TWINSPAN analysis identified three site groups. Site group 1 contains 7 sites, which were located in Shazihe transect. Site group 2 contains 5 sites, which were located in Wusman transect. Site group 3 contains 7 sites, which were located in Aqihe transect except for site 10. The site group 3 separated firstly from all the 19 sites by TWINSPAN showed evident difference with other two site groups. The 23 plant species could be also divided into 3 ecological species groups using TWINSPAN analysis. CCA results were consistent with TWINSPAN results. The distribution patterns of plant species were most strongly associated with underground water table, soil moisture and soil pH value. To a lesser extent, distribution of species was associated with soil alkalinity, underground water mineralization and altitude. The major environmental variables are ground water level and soil moisture, and the regression model as below respectively: X1 = -9.5991L + 100.86 (R2 = 0.6459);X2 = 1.65W + 43.011 (R2 = 0.7646). Although the species did not cluster into well-defined groups, loose arrangements of species can be identified which were associated in a similar way with the environmental variables.

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    Seasonal Changes in Vegetation Activity in Response to Climate Changes in China between 1982 and 1999
    PIAO Shilong, FANG Jingyun
    2003, 58 (1):  119-125.  doi: 10.11821/xb200301014
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    In the present study, using normalized difference vegetation index (NDVI) as an indicator of vegetation activity, seasonal trends of vegetation activity and their dynamic responses to climate changes in China were explored based on remotely sensed data (NOAA-AVHRR) from 1982 to 1999. As a result, spatially averaged seasonal NDVI in China showed a pronounced increase in all four seasons (spring, summer, autumn and winter) during the past 18 years. The average spring NDVI indicated the most significant increase (P<0.001) with a mean rate of 1.3%, while the average autumn NDVI showed the least increase (P=0.075). Analyzing interannual changes in seasonal mean NDVI by vegetation type, it was found that the advance of growing season was a major way for response of vegetation activity to climate changes and that the way exhibited a large regional heterogeneity. In the past 18 years, regions with the largest increase rate of summer NDVI appeared in Northwest China and the Tibetan Plateau, while areas with that of spring NDVI occurred in the eastern part of the country.

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    Spatial Pattern and Component Structure of Forests in Guizhou
    YAO Yonghui, ZHANG Baiping, ZHOU Chenghu, LUO Yang, ZHU Jun,CEN Gang, LI Baolin, CHEN Xiaodong
    2003, 58 (1):  126-132.  doi: 10.11821/xb200301015
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    ArcGIS processing of remote sensed and investigated data of Guizhou forest resources in 2000 gives rise to forest resource distribution map, forest age class structure, and the distribution map of forest canopy. Analysis of these data shows that: (1) though there are multiple types of forest resources, forest coverage is low (only 25.27%, excluding sparse woodland, shrub and underage-forest);(2) the geographical distribution of forests is quite uneven, mainly in the southeast of the province and in Zunyi prefecture; (3) the zonal evergreen broad-leaved forests have been seriously destroyed, and the forest has obvious secondary features, with coniferous forest and shrubbery accounting for the greatest proportion of Guizhou forest; (4) the area of timber-forest is much larger than that of shelter-forest and economic forest; (5) young-and-middle age forests account for greater proportion than near-and-over matured forest; and (6) the forest of Guizhou is not enough to effectively protect the environment of karst mountain areas of the province.

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    Dynamic Analysis and Evaluation of Xinjiang Forest Resources: Based on Remote Sensing and GIS
    LI Hu,, LU Xunxian, CHEN Shujiang, HOU Ping
    2003, 58 (1):  133-138.  doi: 10.11821/xb200301016
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    The variation and evaluation of Xinjiang forest resources were studied based on RS and GIS. The forest resources data in Xinjiang were obtained by using sampling method and by satellite image analysis with ground investigations. Based on GIS, the variation of Xinjiang forest resources from 1996 to 2001 was studied. As a result, the five-year variation of forest resources in Xinjiang is that not only the forestland, woodland, thin stocked land, seed plot, and proper woodland extended, but the forest cover rate and growing stock also increased. The region's woodland increased from 17,331 km2 to 17,837 km2, forest cover rate extended from 1.05% to 1.08%, growing stock increased totally from 2.62×108 m3 in 1996 to 2.90×108 m3 in 2001, a year-on-year increase of 551.40×104 m3. Per ha growing stock increased from 141.198 m3 in 1996 to 147.703 m3 in 2001, an increase of 6.505 m3. According to analysis in this paper, Xinjiang forest resources trend to increase generally, but the problem is that natural forests are sparse, forest cover rate is low, wood age structure is imbalanced. At present and in a certain period of time in the future, efforts should be made to natural forest protection projects, forest management according to classification and regional desertification control in Xinjiang's forestry.

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    The Distribution of Soil Erosion in China at the End of the 20th Century
    XU Feng,, GUO Suoyan, ZHANG Zengxiang
    2003, 58 (1):  139-146.  doi: 10.11821/xb200301017
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    This paper discussed the Spatial Distribution of Soil Erosion in China at the end of the 20th century basing on the second national soil erosion survey. The result indicated that soil erosion is still the first environmental problem in China. Soil erosion mainly occurs in the western region of China, and the slight erosion type exerts great impact on spatial erosion pattern. The distribution of hydraulic erosion shows the impact of landforms, namely, slight hydraulic erosion mainly occurs in mountainous and hilly areas, and half of the serious erosion occurs on the loess landforms. Farmland, forest land and grassland are the major landuse types of the slight hydraulic erosion, while the serious hydraulic erosion and slight wind erosion are mainly distributed on grassland. Thus, the protection and rehabilitation of the grassland is a key to either hydraulic and wind erosion control. The loessal soil (a major type of cultivated soil developed from loess mother material) is facing the most serious threat of soil erosion in China's soil resources. Further discussion on soil erosion distribution needs more research on the method and relevant data analysis.

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    Losses of Nitrogen Nutrient in Overland Flow from Farmland in Beijing under Simulated Rainfall Conditions
    HUANG Manxiang, ZHANG Shen, ZHANG Guoliang, ZHANG iumei
    2003, 58 (1):  147-154.  doi: 10.11821/xb200301018
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    Rainfall simulation experiments were performed to evaluate the contribution of both particulate N and dissolved N to losses of nitrogen by comparing the difference of the N concentrations and the yields in runoff from three tilled plots A, B and C, and the effect of fertilizer applications on them. The catchment area of the plot is 2 m × 5 m each with a slope of 5 degrees. A and B were bare and unfertilized, and C was fertilized with granular urea (360 N kg/ha) idle 35%. These results indicate that: (1) higher rainfall intensity results in higher discharge, sediment yield and losses of N, even lower cover rate significantly reduces discharge, and sediment yield and loss of N; (2) particulate N was the dominative form of N loss in surface runoff, added fertilizer N may suffer loss by runoff dissolved N form. Mechanism of soil aggregates detachment by rainfall and loss by runoff was investigated to seek explanation for the enrichment of PN in eroded sediment to original soil. The results showed that the aggregate size distribution of the eroded sediment was drastically different to that of the original soil. Aggregates smaller than 0.25 mm constituted more than 81% of the sediment as compared with only 16% in the original soil. More than 99% of total N transported by runoff was in the particulate form, whereas 78% of particulate N lost with finer aggregates smaller than 0.25 mm. About 44% of particulate N lost with finer aggregates smaller than 0.045 mm. ERN decreased as the erosion process continued. A higher percentage of aggregates smaller than 0.25 mm, especially the enrichment of aggregates smaller than 0.045 mm which has a high concentration of nitrogen is responsible for the enrichment of N in eroded sediment.

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