Climatic and anthropogenic drivers of land use/cover change in fragile karst areas of southwest China since the early 1970s: a case study on the Maotiaohe watershed

Land use/cover change and its driving forces has been one of the most important fields in global environmental change research since the 1990s. Karst areas are distributed extensively on the Earth’s surface and are usually characterized by a fragile eco-environment. In southwest China, karst landforms are fully developed and their eco-environment is highly fragile. Over the past decades, irrational land use practice has caused a series of alarming eco-environmental issues including forest clearing, soil erosion, and karst rocky desertification. Therefore, it is of great practical significance to study land use/cover change in this area and its driving forces in order to re-build the damaged eco-environment and achieve sustainable land use. In this paper, the authors conduct a case study on land use/cover change and its natural and human driving forces since the early 1970s in southwest China’s Maotiaohe watershed. The results indicate that the land use/cover pattern in the study area has undergone a very complex change, which is a result of combined action of both natural and anthropological factors. In the 1970s and 1980s, climate change and fast population increase played dominating roles in the change of arable land, shrub land, grassland, and rocky desertification land. Since the early 1990s, economic development has gradually taken the place of population change to become the overwhelming human factor to go along with climate change in driving the land use/cover change, particularly the change in arable land, construction land, and rocky desertification land.     

Land use history and status of land desertification in the Heihe River basin

An analysis, over historical times, of the influence of natural factors such as climate, geological activity, existing landforms, and the activity of aeolian sands on the desertification of oases and other lands in the Heihe River basin of northwestern China revealed that desertification occurred more or less quickly according to whether the prevailing climate was cold or warm, respectively. In the 1990s, the area of desertified lands in the lower reaches of the Heihe River (Ejin region) was 29.1% greater than in the mid 1980s. However, the rate of desertification in the middle reaches of the Heihe River basin was relatively slower, only 9.4% from 1949 to 1990 (or 0.27% per year). Since 1990, the rate of desertification has been stable. By 2000, the total area of land desertification in the mid to lower reaches of the Heihe River basin was 13,508.4 km², or 11.8% of the region monitored. Of the total land desertification area, the regions of Linze, Gaotai, Sunan, Jiuquan, Jia Yuguan, and Jinta accounted for 1.70, 1.71, 1.43, 0.85, 0.28, and 9.39%, respectively, whereas the Ejin region’s 11,434.64 km² accounted for 84.65%, indicating that land desertification in the lower Heihe River basin was particularly severe. The causes responsible for the occurrence and development of land desertification in the Heihe River basin were analyzed.     

The relations between land use and karst rocky desertification in a typical karst area,China

Karst rocky desertification (KRD) is one major type of desertification which is under irrational human impact on the vulnerable eco-geo-environment. In this study, Zhudong fengcong rocky desertification landscape was selected to investigate the land use types distribution law in different rock types and the KRD land in different land use types. KRD data was determined by user–computer interactive interpreting method from Aster images in 2004, according to the exposed ratio of rock, the coverage of vegetation and soil in 0.2 km² unit, integrating with land utilizing present situation map, hydrogeology map, relief map, vegetation map, soil distribution map, as well as the practical investigation and the population census datum in 2002. Results showed that the occurrence ratio of KRD land is different in land use types and rocky assemblages obviously; land cover has a strong impact upon KRD. The sloping cropland distributed in homogenous limestone has a higher occurrence ratio of light KRD, secondly, is in the limestone interbedded with clastic rock. Light KRD land was dominated by shrubland, and sloping cropland accounts for 11.67% of it, moderate KRD land was dominated by moderate coverage grass slopes, strong and extremely strong KRD was dominated by rocky dry land which is difficult to use.     

Re-evaluating the impacts of human activity and environmental change on desertification in the Minqin Oasis, China

The Minqin Oasis and its adjacent regions in northern China experienced significant desertification beginning 2,000 years ago and continuing to the present, and numerous studies have claimed that human activities, especially the flourishing of agriculture, have played a major role in environmental change in this region. Our analysis suggests that the observed desertification was mainly controlled by changes in the water component of the ecosystem and the arid climate. The impacts of cultivation on desertification from 2,000 years ago to the mid-1900s appear to have been relatively minor compared to the impacts of the area’s arid climate and its native geomorphological processes. Although human activity has increased from the late-1940s to the present, and the areas of the oasis reclaimed for agriculture have reached a maximum, desertification over the past 50 years appears to be a continuing process that began thousands of years ago, and is mainly controlled by decreasing water levels caused by the arid climate, local geomorphological processes and overuse of water in the upstream. Although both human activities and climate variation are important drivers of the desertification process, and it is not possible to completely separate the human influence from the climate impact, key factors on controlling desertification should be investigated before we place the blame solely on the flourishing of agriculture in this region.     

Aeolian desertification and its causes in the Zoige Plateau of China’s Qinghai–Tibetan Plateau

Studies and efforts to control aeolian desertification in China have focused on the arid and semiarid lands in the north. However, the aeolian desertification that is occurring on the high-altitude Qinghai–Tibetan Plateau, which has a cold and humid climate, has received attention only in recent years. In this paper, we report the results of monitoring this aeolian desertification between 1975 and 2005 and of our analysis of its causes on the Zoige Plateau, which is located in the northeastern part of China’s Qinghai–Tibetan Plateau. Aeolian desertified lands expanded at a compound annual rate of 4.07% between 1975 and 2005. They expanded most rapidly between 1975 and 1990, at an annual rate of 7.73%. Factors responsible for this expansion include increasing temperature, decreasing precipitation, over-grazing, drainage of water systems, and land reclamation for agriculture. Increasing temperature, over-grazing, and the drainage of water systems were the key factors. The climatic variations between 1975 and 2005 were not sufficient by themselves to lead to aeolian desertification. Human disturbances such as over-grazing and drainage of water systems must thus have been primarily responsible for the observed changes, and human behavior must be adjusted to control the expansion of aeolian desertification and rehabilitate the desertified lands.     

遥感与GIS支持下的松嫩平原农牧交错区土地沙漠化调查研究

以1986年和2000年两个时期的LANDSATTM数据作为主要信息源,对松嫩平原农牧交错区的土地沙漠化现状、程度和发展趋势进行遥感解译和实地调查。分析研究结果表明:区域内的土地沙漠化总体上呈逆转趋势。主要表征为沙漠化土地面积减少,平均每年减少0.71×10⁴hm²,年递减率为0.8%;沙漠化程度渐轻,微度沙漠化土地增加92.9%,而轻、中、重度沙漠化土地减少了44.3%。该地区的土地沙漠化整体上以逆转趋势为主,还有一些局部区域沙漠化程度仍在发展,土地沙漠化的状况不容忽视。人类活动对区域土地沙漠化的影响比较明显,气候变化和地理环境也对土地沙漠化产生重要的影响,沙漠化土地类型由以草地为主转为以旱地为主。     

石羊河流域植被指数时空变化及荒漠化遥感监测

利用SPOT VGT NDVI数据对石羊河流域1999—2010年期间植被覆盖的时空变化进行了研究,并基于像元二分模型求算植被覆盖度,以植被覆盖度为指标对研究区荒漠化程度进行定量监测与评价。结果表明:12年来石羊河流域植被覆盖度整体呈增加的趋势,增加速率为0.003 2 a-1。植被改善的面积远大于植被退化的面积,植被改善区域的面积为11 130 km2,占研究区总面积的26.45%,主要分布在金昌、永昌、民勤、武威东部以及古浪的西北部地区;植被退化区域的面积为3 546 km2,占研究区总面积的8.43%,主要分布在天祝藏族自治县的东部和古浪南部的乌鞘岭地区。荒漠化土地面积整体呈下降的趋势,极重度荒漠化土地明显减少,转化为重度荒漠化;非荒漠化土地的增加主要以绿洲的扩张为主。     

Rocky desertification and its causes in karst areas: a case study in Yongshun County,Hunan Province,China

Rocky desertification, a process of land degradation characterized by soil erosion and bedrock exposure, is one of the most serious land degradation problems in karst areas, and is regarded as an obstacle to local sustainable development. It is well known that human activities can accelerate rocky desertification; however, the effects of climate change on rocky desertification in karst areas are still unclear. This study focused on the effects of temperature and precipitation changes and human activities on rocky desertification in karst areas to determine the impacts of climate change and human disturbances on rocky desertification. Areas of different level of rocky desertification were obtained from Landsat TM (1987) and Landsat ETM+ (2000) images. The results show that, although the total desertification area increased by only 1.27% between 1987 and 2000, 17.73% of the slightly desertified land had degraded to a moderate or intense level, 2.01 and 15.71%, respectively. Meanwhile, between 1987 and 2000, the air temperature increased by 0.7°C, and precipitation increased by 170 mm. Statistical results indicate that the increase in precipitation was caused by heavy rainfall. In addition, under the interactive influences of heavy rainfall and temperature, the average karst dissolution rate was about 87 m³ km⁻² a⁻¹ during the 14 years in the study area. Further analysis indicated that rocky desertification was positively related with the increase in temperature and precipitation and especially with the heavy rainfall events. Climate change accelerated rocky desertification in the karst areas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Changes in soil physical and chemical properties during reversal of desertification in Yanchi County of Ningxia Hui autonomous region,China

Using field surveys and laboratory analysis, soil physical and chemical properties were studied at a site exhibiting the reversal of desertification in Yanchi County of China’s Ningxia Hui autonomous region. The dominant soil particle size changed from coarse-fine sand to a combination of very fine sand and silt + clay, and corresponding levels of each soil nutrient increased. The content of coarse-fine sand (2–0.1 mm) was significantly and negatively correlated with soil nutrient contents, whereas nutrient contents were significantly and positively correlated with the contents of very fine sand (0.1–0.05 mm) and silt + clay (<0.05 mm). The increasingly fine soil texture and the nutrient enrichment both facilitated rehabilitation of desertified land. The silt + clay content contributed the most to the increasing soil nutrient contents, and thus appears to be the key factor in reversal of desertification. Soil nutrient concentrations in the bulk soil increased with increasing content of soil nutrients with different particle fractions, and there were significant positive correlations between them. The nutrients in all particle size classes jointly decided the effect of soil nutrient contents on the reversal process. Principal-components analysis (PCA) revealed that the soil quality tended to increase during the reversal process, and that nutrient factors were more significant than particle size (i.e., were the dominant factor that influenced soil quality). Available nutrients and soil organic matter (SOM) were the most important nutrient factors. Silt + clay were the most important particle factors.     

花江喀斯特峡谷地区石漠化成因初探

花江喀斯特峡谷区地下水埋藏深,地表干旱,存在显著的人为加速土壤侵蚀过程,植被次生性明显,生境干热特征显著,是已石漠化和半石漠化的生态系统。其中地质构造、地貌演化、岩溶形态、可开发利用的水资源、植被群落可能是石漠化过程的主要自然成因,以土地利用为表现形式的强烈人类活动是石漠化的驱动力。基于此,提出了石漠化地区的土地利用方式和生态恢复过程的建议,旨在为石漠化的演化研究及生态重建提供参考。     

基于RS、GIS的重庆黔江区石漠化现状与成因分析

在RS、GIS支持下,利用2004的TM遥感影像数据研究重庆市黔江区石漠化现状及形成原因。结果表明:黔江区7.21%的土地发生石漠化,其中轻度、中度、强度石漠化分别占总面积的3.06%、3.41%、0.74%,潜在石漠化占总面积的4.84%;石漠化的分布与地层、高程、坡度及土地利用等因素密切相关;石漠化的形成与发展是人类不合理的经济活动叠加于脆弱的生态地质环境背景上综合作用的结果。     

Assessing changes in the rainfall regime in Nigeria between 1961 and 2004

The study assessed changes in the rainfall regime in Nigeria between 1961 and 2004 in terms of (a) absolute seasonality—the length of dry and wet season; (b) relative seasonality—rainfall contrast during the year; (c) number of rainfall maxima and minima; and (d) timing of rainfall maxima and minima. Trends in the mean monthly surface locations of the Inter-tropical Discontinuity (ITD) were also examined as a prominent factor of the rainfall regime. Changes in the regime were examined over four time slices: 1961–1971, 1972–1982, 1983–1993 and 1994–2004. The results show that, in the area of single rainfall maximum regime, the length of the wet season has increased from 4 months (in 1961–1971) to 5 months (since 1972–1982). The rainfall relative seasonality has consistently been ‘most rain in 3 months or less’. The rainfall maxima still indicate single rainfall maximum but shift in the peak from August to July. Rainfall during the months of June to September appears to have witnessed declining trends over the first three time slices. The last time slice however indicates trends towards a wetter condition. For the area of double maxima rainfall regime, the length of the wet season has consistently been 8 months. The rainfall relative seasonality has consistently been ‘rather seasonal with a short drier season’. The rainfall maxima and minima still indicate double rainfall maxima with August as the month of the minimum but shift in the primary peak from July to September. The northward latitudinal distance of the surface location of the ITD from the equator indicates significant upward trends during the months of May to September only and for a period of 1983–2000. The trend results of the ITD appears to account for most of the observed changes in the rainfall regime in Nigeria.     

Spatial pattern of Karst rock desertification in the Middle of Guizhou Province,Southwestern China

Karst rocky desertification is a typical type of land degradation in the Southwestern China. It has great ecological and economical implications for the local people. Landsat images from the middle of Guizhou Province collected in 1974, 1993 and 2001 were used for change detection of the pattern of Karst rocky desertification. The results show the following findings: (1) Desertification area expanded drastically in 27 years, at an increasing rate about 116.2 km²/year. (2) High areas (900–1,500 m) are the most affected. (3) Areas with the slope <5° or >25° are also easily tend to be Karst rocky deserted. (4) The process of Karst rocky desertification is nearly irreversible. Few areas of Karst rocky desertification could be meliorated to non-desertification land. (5) Most of the degraded lands are located in the south and the central of the study region, and the meliorated land areas are sparsely located in the east and the west part of the region. All these findings would provide bases for the decision-making of the local government to improve the Karst rocky desertification     

Quantitative Analysis of Natural and Human Factors of Oasis Change in the Tail of Shiyang River over the Past 60 Years

The human and natural factors complicit in the driving forces of oasis change have always received considerable interest from the international research community. In this study, we used principal component analysis of natural and socio-economic statistical factors to quantitatively analyze the causal relationships and their contributions to the observed periodic expansion or shrinkage of the Minqin Oasis over almost 60 years. Our results show that human factors were the dominant factors governing expansion or shrinkage, with average contributions of 69.38% and 76.16%, respectively. Moreover, policy decisions have been the pivotal human factors. Under the influence of various policies, we have found that water resource utilization, land reclamation, population explosion, ecological protection and economic development have each played leading roles in different periods. This study provides a scientific basis for modelling the dynamics of an oasis for sustainable management.     

Streamflow changes and its influencing factors in the mainstream of the Songhua River basin,Northeast China over the past 50 years

The Songhua River plays a key role in the national development of China, owing to its unique natural condition and resources. Recent changes in the streamflow in the Songhua River are important with regard to local sustainable development and management under the background of global warming and aggravating soil erosion. In order to detect changes in the streamflow, two streamflow series from 1955 to 2004 (observed at the Harbin and Jiamusi stations) in the mainstream of Songhua River basin were obtained, and methods of statistical analysis, wavelet transform, and double mass analysis were employed to analyze the data. Reasons for the changes to the streamflow are discussed with respect to natural and man-made drivers. The results show the following: (1) From 1955 to 2004, the streamflow series present obvious declining trends. (2) The streamflow series followed the pattern of a wet–dry–wet–dry cycle pattern over the past 50 years. In the mainstream of Songhua River, wet years mainly occurred during the periods of 1955–1966 and 1984–1993, while dry years mainly occurred in the 1970s and after 2000. (3) Within the 50-year scale, the streamflow series appeared in the main periods of circa 33-, 13- and 4-year, in which the 33-year periodicity is the strongest. (4) Precipitation and temperature directly influenced the streamflow in the mainstream of the basin. The discharge was positively correlated with the precipitation and negatively correlated with the temperature. In addition, human activity was another important driving factor for streamflow change. (5) In the mainstream of Songhua River basin, the influences on streamflow can be divided into three periods: 1955–1976, 1977–1997, and 1998–2004. In the first period climate change played a dominant role, and during the latter two periods human influences were enhanced significantly.     

中国土地荒漠化的概念、成因与防治

荒漠化是指人类历史时期以来,由于人类不合理的经济活动和脆弱生态环境相互作用造成土地生产力下降,土地资源丧失,地表呈现类似荒漠景观的土地退化过程。在中国北方荒漠化形成因素中过度放牧占30．1％,过度农垦占26．9％,过度樵采占32．7％,水资源利用不当占96％,工矿交通建设中不注意环境保护占0．7％,在地区上以北方农牧交错及旱农地区荒漠化最为严重。要采取因地制宜措施和建立健全而完善的治理实施系统以达到生态、经济和社会三个效益的目的。     

Relationships between rocky desertification and spatial pattern of land use in typical karst area,Southwest China

Karst rocky desertification is a typical type of land degradation in the Southwest China. An attempt was made to study quantitatively the relationships between rocky desertification and spatial pattern of land use through applying spatial analysis of Geographical Information System in Nandong underground river system, a typical karst area, Southwest China. The spatial distribution of rocky desertification and spatial pattern of land use were obtained from interpreting Landsat Images in Nandong area in 2007 by supervised classifications, and verified and rectified through field survey. The results indicate that: (1) the total land deserted area covers 378.3 km², or 23.4% of the total area, of which intense, moderate and slight rocky desertification covers 269.46, 54.2, and 54.63 km², respectively, in Nandong area. (2) There is an obvious effect of spatial pattern of land use on rocky desertification. With the increase of elevation and slope, there is a higher occurrence ratio of rocky desertification in the cultivated land and grass land. Also, more than half of total rocky desertification was dominated within the areas of 4 km from the construction land, and 97% of total rocky desertification was dominated within the areas of 10 km from the construction land in Nandong area. And what can be known from the data is that the primary effect distance of human on rocky desertification from the construction land is 4 km, and the farthest effect distance of human on rocky desertification from the construction land is 10 km in Nandong area.     

Diatoms from surface sediments of Enderby Basin of Indian Sector of Southern Ocean

Diatoms from surface sediment samples collected from Enderby Basin of Indian Sector of Southern Ocean were analyzed to determine the relative abundance and distribution of seven key indicator diatom species viz. Sea ice related species Fragilariopsis rhombica, F. separanda, F. curta, F. ritscheri, Thalassiosira tumida and Actinocyclus actinochilus and Open Ocean species F. kerguelensis on the basis of modern physico-chemical parameters. The relative abundances of different species observed viz. F. rhombica — 6.25%; F. separanda — 12.5%; F. curta — 10.53–13.33%; F. ritscheri — 4.55–12.5%; F. kerguelensis — 6.25–63.64%; T. tumida — 3.13% and A. actinochilus — 9.38–13.33%. The increasing abundance of F. kerguelensis consecutively suggests the effect of Antarctic bottom water in the study area which is further substantiated by the presence and increasing abundance of F. ritscheri. The gradual decrease in abundance or absence of sea ice related species from the sampled stations indicates the summer and winter sea ice extent concentration in the study area. The nutrient concentration correlates with the distribution and abundances of diatom species.     

Environmental degradation in the Hexi Corridor region of China over the last 50 years and comprehensive mitigation and rehabilitation strategies

The regional hydrology and ecosystems of the Hexi Corridor region of northwestern China have changed over the last half century under the driving force of intense human activity and regional climate changes. Streamflow issuing from mountains in the eastern section of the Corridor by way of the Shiyang River has decreased significantly. Annual mountain outflow from the Heihe and Shule Rivers in the central and western portions of the Corridor, respectively, have tended to increase; however, their downstream discharge has decreased sharply. These lower reaches clearly display anthropogenic hydrological features. Water salinization and pollution have worsened. Presently, up to 208 km of river courses exhibit the poorest water pollution grades of IV and V. Overall, the forested area in the south Qilian Mountain region has decreased by 16.5% in the last 50 years, but has recently begun to show a gradual increase. However, natural desert forests in the northern portion of the Hexi Corridor have continued in a trend of degradation and rapid disappearance, with 3431 km² lost in Minqin and Ejin counties alone. Grasslands have been progressively degraded and their area decreased such that grasslands in the Hexi Corridor region only cover 46.86% of their former area. Desertification has been exacerbated and the grasslands' stock capacity reduced. In the Hexi Corridor region desertification has proceeded swiftly over the last 50 years, reaching, in the early 1980s, a maximum annual rate of 2.15% of total initial grassland area. However, from the late 1980s through the 1990s their desertification rate has dropped significantly. A unified watershed-scale plan for water use and management in different regions of the Hexi Corridor, considering water demands for economic development as well as ecosystem maintenance and remediation, must be implemented. The improved and ultimate sustainability of regional development for the Hexi Corridor is linked to following ecological criteria in exploiting land resources, and to systematically protect ecosystem function, allowing for sound ecosystem development.     

Assessment of deforestation,biodiversity loss and the associated factors: case study of Ijesa-Ekiti region of Southwestern Nigeria

Deforestation is driven by a variety of factors, and has resulted in land use changes that threaten biodiversity, water and energy resources. However, lack of reliable data and survey information in Nigeria has made the estimation of the effect of deforestation difficult to establish. Consequently, the extent and rate of deforestation are less well known. The study therefore, examined and analyzed the spatial and temporal patterns of deforestation over the period of 25 years (1978–2003); measured the rates, trends and explained the factors that determined deforestation in Ijesa-Ekiti region of southwestern Nigeria. The major sources of data for the study were satellites images. These were Landsat MSS 1978, with spatial resolution of 80 m, SPOT XS 1986, SPOT XS 1994, with 20 m spatial resolution and NigeriaSat_1 2003, with 32 m spatial resolution. To make them comparable, they were georeferenced to the same coordinates system, filtered, resampled and enhanced for visualization in a GIS environment. Furthermore, Ilesa, Ijebu-Ijesa, Efon-Alaaye, Iloko-Ijesa, Erin-Oke and Erin-Ijesa were identified and selected for ground truthing to validate the tonal values recorded in the images with the features on the ground. The result of ground truthing was combined with visual image interpretation as training sites for supervised classification. Focus Group Discussions were held with people who had lived in the area for over 20 years as a means of eliciting factors of deforestation and the effects on forest biodiversity. The results indicated forest loss of 53,469.23 ha over the period of 25 years at an annual deforestation rate of 7.21, 2.47, and 5.40% per year for 1978–1986, 1986–1994 and 1994–2003, respectively. FGDs with various categories of people in the bigger towns confirmed deforestation in the area and were due to illegal lumbering, intensive agricultural practices and growth of settlements resulted from increase in human population. FGDs also revealed extinction of many forest species in their communities. In conclusion, the study advanced our understanding on techniques of analyzing deforestation using geo-spatial technology. It also generated a synthesis of information on the rates of deforestation and its driving forces, which are a complex mix of anthropogenic factors, the chief of which has been the conversion of forest resources to agricultural land use.