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1.
Agricultural areas are declining in many areas of the world, often because socio-economic and political changes make agriculture less profitable. The transition from centralized to market-oriented economies in Eastern Europe and the former Soviet Union after 1989 represented major economic and political changes, yet the resulting rates and spatial pattern of post-socialist farmland abandonment remain largely unknown. Remote sensing offers unique opportunities to map farmland abandonment, but automated assessments are challenging because phenology and crop types often vary substantially. We developed a change detection method based on support vector machines (SVM) to map farmland abandonment in the border triangle of Poland, Slovakia, and Ukraine in the Carpathians from Landsat TM/ETM+ images from 1986, 1988, and 2000. Our SVM-based approach yielded an accurate change map (overall accuracy = 90.9%; kappa = 0.82), underpinning the potential of SVM to map complex land-use change processes such as farmland abandonment. Farmland abandonment was widespread in the study area (16.1% of the farmland used in socialist times), likely due to decreasing profitability of agriculture after 1989. We also found substantial differences in abandonment among the countries (13.9% in Poland, 20.7% in Slovakia, and 13.3% in Ukraine), and between previously collectivized farmland and farmland that remained private during socialism in Poland. These differences are likely due to differences in socialist land ownership patterns, post-socialist land reform strategies, and rural population density.  相似文献   

2.
A decade back, almost 300,000 km2 of forests in India were estimated to be potential tiger habitat. But consistent degradation and unsustainable anthropogenic pressures have adversely affected tiger presence in most of the forests outside the better protected tiger reserves. Here we use Geographic Information System data to analyze the degree of vegetation loss and landscape changes over the last decade (1998–2006), and ascertain the presence of tigers in a degraded forest like the Kawal Wildlife Sanctuary, Andhra Pradesh, India, by non-invasive fecal DNA analysis. Vegetation cover maps show a clear degradation of the sanctuary within a decade. DNA analysis of scat samples reveals tiger presence in areas where closed dense forest canopy has persisted with minimal human disturbance during the last decade.  相似文献   

3.
4.
An indicator of quantifying eco-environmental vulnerability was established by synthesizing 12 variables, mainly retrieved from satellite data with incorporation of analytical hierarchy process (AHP). Six vulnerability levels of potential, slight, light, medium, heavy, and very heavy were graded to depict changes of vulnerability over temporal and spatial scales. The proposed approach was employed to study spatiotemporal eco-environmental vulnerability with Landsat data acquired in 1989, 2003, and 2014 for the Thua Thien – Hue Province, Vietnam. Over the time periods of 1989–2003 and 2003–2014, both heavy and very heavy vulnerability levels exhibit an increasing trend in both magnitude and spatial size: The former raised from 5.9% in 1989, to 7.9% in 2003, and 15% in 2014; and the later increased from 1.2% in 1989, to 3.2% in 2003, and 7.3% in 2014. Both levels mainly appeared on urbanized area, bare land, semi-bare land, agricultural land, and sparse forests. In contrast, there was a significant decline in potential vulnerability level with 36.4% in 1989, 30.9% in 2003, and 19.2% in 2014, while the remaining vulnerability levels slight, light, and medium fluctuated slightly, increased in 2003 and decreased in 2014. Supporting reasons for such changes include: (1) deforestation, agriculture intensification, construction of three hydro-electric projects during the period 2003–2014; and (2) significant expansion of urbanized area leading to differences in thermal signatures in urban areas as compared with rural areas. The findings demonstrate that eco-environmental vulnerability is primarily exaggerated by anthropogenic activities through land use/land cover (LULC) changes and further enhanced by natural processes including disasters in the Thua Thien – Hue Province of Vietnam. The correlation between land surface temperature (LST) and Normalized Difference Built-up Index (NDBI) is found to be positively correlated with 0.87, 0.89, and 0.84 for 1989, 2003, and 2014, respectively. In contrast, LST-Normalized Difference Vegetation Index (NDVI) is found negatively correlated with respect to the spatiotemporal trend of environmental vulnerability with −0.81, −0.81, and −0.76 in 1989, 2003, and 2014, respectively. In addition, areas having potential, slight, and medium thermal environmental levels are decreased from 1989 to 2003 to 2003–2014. At the regional scale, increased anthropogenic activities through land’s modification have intensified the eco-environmental vulnerability in the study area. The currently proposed methodology is feasible for evaluating long-term eco-environmental changes processes by using remote sensing data, and valid for the other regions.  相似文献   

5.
All nine wetland lakes in the CASSARINA North African suite of sample sites have been disturbed strongly by human activity during the 20th century. Dated lake sediment core were used to provide evidence of the extent of recent environmental change at each site. Sedimentary diatoms at seven sites were useful for inferring salinity change trends during the last century. At two sites preservation problems severely degraded the sedimentary diatom record. Sediment core integrity was otherwise established.Lithostratigraphic measurements indicated some site specific changes in soil erosion and sediment composition but, for the Egyptian Delta lakes, no physical signal synchronous with Aswan High Dam construction was found. Sedimentary diatom assemblages were generally site characteristic and halophilous taxa were common. At two sites planktonic diatoms indicated some recent eutrophication but generally the assemblages were more indicative of salinity changes. Diatom-inferred salinity trends for the seven sites typically indicated that reductions in water salinity occurred sometime during the early or mid 20th century.Rather than climate, hydrological modification of water resources is implicated as the primary driver of salinity changes during most of the 20th century. In the western North African region these modifications were mainly local land drainage and water diversion programmes to alleviate winter flooding and/or promote summer water availability. In the Delta region, the Nile has been intensively exploited since antiquity and intensively so from the late 19th century to release more fresh water for agriculture. Here, diatom records indicate that freshening began well before the Aswan High Dam but salinity fluctuations have tended to diminish during the latter part of the 20th century. A small reversal in the water freshening trend in the 1980/90s was possibly a response to land subsidence/sea-level change or to reduced freshwater supply.Freshwater supply to the sites is generally diminishing as former freshwater surpluses switch to deficit. One site (Merja Bokka, Morocco) became completely dry in 1998 as agriculture encroached and Megene Chitane, the only acid lake in Tunisia, is currently affected by excessive inflow abstraction. At the beginning of the 21st century, eight of the nine CASSARINA sites persist as viable but modified aquatic ecosystems. They nevertheless continue to support valuable aquatic biodiversity, especially in the Delta sites and in Chitane. The modern diatom communities are clearly tolerant of considerable environmental change but the remaining sites are increasingly threatened by major hydrological disturbance. Base-line floristic data for the late 20th century are given but continuous biomonitoring combined with effective management is needed urgently to help conserve North Africa's diminishing natural wetland lake resources.  相似文献   

6.
Brazil’s Atlantic Forest biome is severely degraded and fragmented throughout its range. Developing effective techniques to restore pasture and agriculture back to native vegetation is therefore a priority for legal and conservation purposes. In this study, we evaluate the ability of artificial bird perches to enhance the arrival of new seeds and seedling establishment in a degraded, semi-deciduous seasonal portion of the Atlantic Forest in southern Brazil. Specifically, we assess the influence of previous land use and habitat types on the abundance, species richness and ecological traits of bird-dispersed seeds, as well as on seedling establishment. Eight sampling sites were established, each containing one unit with seed traps and restoration plots under artificial perches and one similar unit without the perches. These sites were located in pasture and agriculture, distributed between riparian and sub-montane areas. Monthly sampling was conducted over two years between December 2005 and November 2007, resulting in the evaluation of 25,755 seeds and 56 endozoochoric seed species. The most abundant species were the pioneers Cecropia pachystachya Trécul and Solanum americanum Mill. Experimental units with perches received significantly more seeds than control units. Moreover, seed arrival was higher in sub-montane areas and on former pasture sites. Species richness followed a similar pattern of higher seed arrival, but there was no effect of vegetation type. Ecological characteristics of seeds were associated with land use type: former pastures received more tree seeds and pioneer species than expected by chance. Seedling establishment was very low in all treatments, with only eight seedlings established in perch plots by the end of the experiment. We conclude that despite artificial perches significantly increasing the arrival of endozoochoric seeds onto degraded lands, seedling establishment is drastically limited in these areas, compromising the efficacy of this technique for restoration purposes.  相似文献   

7.
Rwenzori mountain range is important for its high diversity of unique species and as a water catchment area and yet very fragile to human interference. The study documented the impact of land use on ecology of uncultivated plant species in the Rwenzori mountain range using Bugoye sub‐county as a reference site. The ecological aspects of the plants studied included distribution, abundance and diversity of the plant species in and around the various land uses as well as in degraded, disturbed and undisturbed areas. Land uses identified were; agriculture, built up area and land with other activities (conservation and abandoned fields). The study revealed that agriculture was the main land use category taking up 69.7% of land use area. Plants distributed in and around the land uses were mainly trees with species diversity of 34.5%. Generally, there was no relationship in the distribution of plant species in degraded, undisturbed and disturbed areas (a = 0.01). In disturbed areas, there was vegetation cover especially of plant species that occur as secondary re‐growth, and in degraded areas, the ground was sparsely covered by primary succession species while in the undisturbed areas, plant species growing in a ‘natural. habitat dominated and most of them were climax species.  相似文献   

8.
我国陆地地面水环境近十年来的变化特征及原因分析   总被引:3,自引:0,他引:3  
卢进登  卢晓梅 《生态科学》2002,21(4):370-373
本文根据近十年来我国环境状况公报和有关统计资料,分析了我国陆地地面水环境近十年来的变化特征及其原因。分析表明我国陆地地面水环境近十年来呈现由恶化到基本控制的变化态势;重要的污染源正由工业污染向生活污水和农业面源污染转变,从而提出了相应的污染控制策略。  相似文献   

9.
Land-cover changes in the Choptank basin were estimated for 1665–1820 by using historical socioeconomic data and crop-rotation models. Socioeconomic data (human population, output per laborer, and crop yields) were obtained from the literature, whereas crop-rotation models, based on historical records, represented how agriculture was practiced. Model parameters and output were validated with export records, census data, and other historical records, and model errors were estimated to be approximately 5%. This approach indicated a sigmoidal pattern for conversion of primary forest to agricultural land by 1800. The initial time period, 1665–1720, was characterized by low-intensity tobacco and corn cultivation. Due to long fallows, the models indicated that there was little land in crops (approximately 5% of the region), but larger areas of secondary forest occurred on former cropland (approximately 15%). Although primary forest decreased, the initial result in the first 55 years was a low net rate of deforestation and occupation by low-intensity farms. However, after 1720, cropland expanded rapidly due to the use of wheat as a cash crop. From 1720 to 1775, primary and secondary forest rapidly disappeared, increasing agricultural land to 60% of the region. By 1800, approximately 80% was estimated to be converted to agriculture, and little primary forest remained. After 1800, the land needed for crops decreased due to improved management practices and crop yields, and some secondary forest on formerly cleared agricultural sites may have reappeared. We estimate that less than 150 years of European colonization resulted in virtually complete agriculturalization of a primarily forested landscape.  相似文献   

10.
土地利用/覆被变化(LUCC)是全球变化研究的重要核心问题之一,选择干旱区典型绿洲新疆渭干河—库车河三角洲绿洲为研究靶区,利用1989年、2001年、2006年和2010年的同期遥感影像数据,借助RS和GIS技术,对绿洲土地覆盖变化信息进行定量提取和分析。结果表明:①1989—2001年,各类地物面积呈现五增二减的趋势:耕地、林地、中度盐渍地、水体和其他均有所增加;而轻度盐渍地和重度盐渍地有所减少;2001—2006年,呈现四增三减的趋势:耕地,轻度盐渍地,中度盐渍地和重度盐渍地均有所增加;林地、水体和其他均有所减少;2006—2010年,呈现四增三减的趋势:中度盐渍地,重度盐渍地、水体和其他均有所增加;耕地、林地、轻度盐渍地均有所减少。②随着时间的推移,各类地物的重心均有所偏移。其中水体的重心于1989—2001年间向北迁移的距离最远,为23.12 km;同期重度盐渍地重心迁移距离次之,为22.04 km。林地的重心于1989—2001年间逐年向西南方向迁移,并且迁移的距离逐年增大,中度盐渍地重心总体向西北方向偏移。③21年间,Shannon多样性指数、Shannon均匀度指数均呈稳步增加的趋势,景观的异质性程度呈现上升趋势;聚集度差异不大,集中在78到85之间,说明斑块类型连接程度较高。1989—2006年,分维数增加,研究区的土地利用景观格局愈来愈复杂,人类干扰程度在不断增强;2006—2010年,分维数略有所下降,景观格局略有所改善。总之,21年间渭-库地区各类型土地利用情况变化显著,不仅各土地覆盖类型间面积转换频繁,而且土地利用景观格局发生了很大的变化。该研究确定了土地利用/土地覆被的时空变化规律,分析驱动因子,提出改良建议,研究结果对西部干旱区绿洲的环境演变和可持续发展研究具有现实意义,也是对全球变化研究的重要补充。  相似文献   

11.
Bottomland hardwood forests in the southcentral United States have been cleared extensively for agriculture, and many of the remaining forests are fragmented and degraded. During the last decade, however, approximately 75,000 ha of land—mainly agricultural fields—have been replanted or contracted for replanting, with many more acres likely to be reforested in the near future. The approach used in most reforestation projects to date has been to plant one to three overstory tree species, usually Quercus spp. (oaks), and to rely on natural dispersal for the establishment of other woody species. I critique this practice by two means. First, a brief literature review demonstrates that moderately high woody species diversity occurs in natural bottomland hardwood forests in the region. This review, which relates diversity to site characteristics, serves as a basis for comparison with stands established by means of current reforestation practices. Second, I reevaluate data on the invasion of woody species from an earlier study of 10 reforestation projects in Mississippi, with the goal of assessing the likelihood that stands with high woody species diversity will develop. I show that natural invasion cannot always be counted on to produce a diverse stand, particularly on sites more than about 60 m from an existing forest edge. I then make several recommendations for altering current reforestation practices in order to establish stands with greater woody species diversity, a more natural appearance, and a more positive environmental impact at scales larger than individual sites.  相似文献   

12.
Kenya's Rift Valley has been undergoing rapid land cover change for the past two decades, which has resulted in ecological and hydrological changes. An effort is under way to quantify the timing and rate of these changes in and around the River Njoro watershed located near the towns of Njoro and Nakuru using remote sensing and geographic information system (GIS) methods. Three Landsat TM images, representing a 17‐year period from 1986 to 2003 in which the area underwent a significant land cover transition, were classified and compared with one another. Vegetation diversity and temporal variability, common to tropical and sub‐tropical areas, posed several challenges in disaggregating classified data into sub‐classes. An iterative approach for the resolving challenges is presented that incorporates unsupervised and supervised classification routines in coordination with knowledge‐based spatial analyses. Changes are analysed at three spatial scales ranging from the highly impacted and deforested uplands to the watershed and landscape scales. Land cover transitions primarily occurred after 1995, and included large forest losses coupled with increases in mixed small‐scale agriculture and managed pastures and degraded areas. These changes in cover type are highly spatially variable and are theorized to have significant impacts on ecological and hydrologic systems with implications for environmental sustainability.  相似文献   

13.
The duration of exercise tolerance of the circulatory system in different ethnic populations of Yakutia early in and at the end of the last decade of the 20th century (1988–1989 and 1998–1999) was studied. Compared to the native population (Yakuts), those born in Yakutia (Europoids) demonstrated a higher tolerance at both stages of the study. It was found that the work capacity and exercise tolerance significantly decreased in both ethnic groups during the last decade of the 20th century.  相似文献   

14.
Human impacts on tropical forest dynamics   总被引:2,自引:0,他引:2  
People living near or in tropical forest ecosystems have traditionally extracted forest products, i.e. timber, food and medicinal plants for their livelihood. Such practice does not create too much disturbance when the population is still sparse, and the product is used only for their own needs. When population pressure becomes greater, and when the motive of extraction is profit, then the disturbance become serious and created environmental problems. Major exploitation of the Indonesian rain forest for timber began in the 1960s and is continuing today. The lowland rain forests of Sumatra and Kalimantan have been particularly logged. Exploitation has often been destructive because Forest Department rules have been widely ignored. Moreover, once roads have given access to formerly inaccessible areas, farmers have often moved in after the timber companies and then cleared the relict, regenerating forest for either permanent or shifting cultivation. The traditional shifting cultivations have been practised for years, producing millions of ha of impoverished secondary types of forest, degraded lands and alang-alang (Imperata cylindrica) grasslands. Forests have also been lost through conversion of land to plantation agriculture and transmigration programmes, mining, construction roads and railways and also natural disturbances, such as drought and fire. This paper will discuss the human impact upon tropical forest dynamics in general, with examples from Indonesian and other Southeast Asia countries' tropical forests.  相似文献   

15.
Rapid industrialization and economic growth in South Korea since the 1970s have resulted in severe environmental disturbance and pollution, problems aggravated by the imprudent expansion of urban areas. This paper analyzes and predicts urban growth patterns with the aim of contributing to more efficient urban planning. Urban growth probability index (UGPI) maps were prepared using the frequency ratio (FR), analytic hierarchy process (AHP), and logistic regression (LR) methods, with and without considering development restrictions based on the national environmental conservation value assessment map (ECVAM). Environmental and legal restrictions were associated with an average difference of 41.70% in conservation areas and an 81.32% average difference in agriculture and forest land use–land cover (LULC). Accuracy of the models was examined by area under the curve (AUC) analysis. Accuracies of UGPI maps produced with the ECVAM were higher than UGPI maps produced without the ECVAM. In addition, effectiveness and accuracy tests based on LULC showed that the UGPI maps produced with the ECVAM had a higher rate of accuracy that UGPI maps produces without the ECVAM. Using the ECVAM and assuming that urban and built-up areas will be 1.5 times greater than in 2005 and that environmental restrictions are removed, urban development can be expected to more than double in conservation areas and borderlands, increase by more than 1.5 times in developable areas, and decrease by half in old downtown areas. If legal restrictions are removed, urban development is expected to occur mostly in former conservation areas, followed by borderlands, old downtowns, and developable areas.  相似文献   

16.
 通过处理(根据当地习惯收割凋落物和林下层植物)和保护(无任何人为干扰)样地的比较试验,在10年时间里(1990~2000年)研究了鼎湖山生物圈保护区马尾松 (Pinus massoniana) 林群落植物养分积累动态及其对人为干扰的响应,在此基础上深入和较系统地分析讨论了不同的经营措施对马尾松林可持续性的影响,为我国目前大面积的退化马尾松林恢复和马尾松林可持续性管理提供理论依据。结果表明:1990~1995年,5年时间里由于人为干扰活动而直接从处理样地取走的各元素养分量,在林下层为(kg·hm-2):132.72 (N)、4.72 (P)、63.32 (K)、23.51 (Ca)和7.00 (Mg),在地表凋落物为(kg·hm-2):48.93 (N)、1.85 (P)、17.28 (K)、19.25 (Ca)和2.92 (Mg)。1990~2000年,保护样地林下层和地表凋落物各元素养分贮量分别以39%~41%和37%~38%的年平均增长速率逐年提高,至1995年达到高峰,之后各元素贮量在林下层和地表凋落物均以14%的年平均速率下降。在处理样地,1990~1995年期间各元素贮量在林下层年平均积累速率为17%,之后(1995~2000年期间)则为26%;与此同时,各元素贮量在地表凋落物年平均积累速率为22%~23%,之后(1995~2000年期间)则为28%。在整个试验过程,马尾松林乔木层养分元素总贮量随时间而增加,但其增加的速率随时间和样地不同而异。1990~1995年,保护样地乔木层养分元素总贮量增加了34.9%~38.1%,较处理样地(收获林下层和凋落物)总贮量增加的百分比(29.3%~33.5%)高。然而,1995~2000年,保护样地乔木层养分元素总贮量增加的百分比为26.3%~28.9%,较处理样地(1995~2000年也停止人为干扰)总贮量增加的百分比(28.8%~32.1%)低。可见,1990~1995年,人为干扰活动导致处理样地马尾松林乔木层养分元素年平均积累量降低约1.58%~1.72%,即年平均增长量约减少0.12~2.39 kg·hm-2(2.39 (N)、0.12 (P)、0.77 (K)、1.98 (Ca)、0.29 (Mg)),这些量约相当于每年通过林下层和凋落物收割活动而直接从林地中取走的养分总量的6%~19%。正是由于长期以来受收割林下层和凋落物这种人为干扰的影响,鼎湖山马尾松林乔木层养分贮量较低。这种利用方式不仅直接从林地中取走大量的养分而且还对林地肥力产生间接的负面影响,其结果使该退化林地不能恢复或继续退化。作者建议的森林利用方法代替目前收割林下层和凋落物方式,既可以满足当地居民燃料的需求还有利于马尾松林的自然恢复。  相似文献   

17.
Woodlands dominated by Eucalyptus spp. in temperate southeastern and southwestern Australia have been extensively cleared for agriculture and are often badly degraded by livestock grazing. This has resulted in the loss of biodiversity and widespread land degradation. The continuing decline of these woodlands has become a concern for the conservation of biodiversity, and there is a growing interest among farmers, land managers, and researchers in developing techniques for restoring them. Currently few scientific guidelines exist for undertaking woodland restoration programs. We use a state and transition model to develop hypotheses on restoration strategies for salmon gum (Eucalyptus salmonophloia) woodlands. We consider that this approach provides a suitable framework for organizing knowledge and identifying areas where further information is needed, and hence provides a useful starting point for a restoration program. The model has the potential to provide a tool for land managers with which they can assess the action and effort needed to undertake woodland restoration in agricultural landscapes.  相似文献   

18.
Over the last decade, historically low market prices for Coffea arabica have affected smallholder shade coffee-growing households throughout northern Latin America. In an effort to better understand household response to the coffee crisis and associated landscape changes, this paper examines agricultural production choices and land use patterns among Huastec Maya coffee-growing households. Using data compiled from 47 household interviews, I describe the cultural-geographical landscape in which the Huastec Maya land use system is embedded. In addition, I examine the economics of household production through a financial cost-benefit analysis and through an exploration of the relationship between land availability and land use patterns. Results show that economic inputs and returns from agriculture are highly variable, and that, in 2001, coffee cultivation was not a viable cash-generating strategy for most households. Land availability was found to have a significant effect on land use decisions, especially the proportion of land area devoted to fallow. Most importantly, however, the case study suggests that a purely economic approach does not suffice in explaining why the Huastec Maya continued to grow coffee in 2001, after years of low prices. Household production choices and livelihood strategies must also be viewed within a cultural context.  相似文献   

19.
云南澜沧江流域土地利用和覆盖变化   总被引:10,自引:0,他引:10  
由人类活动引起的土地利用和地被覆盖的变化是地球上环境变化的主要原因。上世纪90年代是云南省经济发展和环境变化的活跃时期。本文通过现代卫星遥感技术、地理信息系统和其它多学科手段相结合 ,系统调查评估了云南澜沧江流域 1990年至 1998年间土地利用和地被覆盖的变化 ,结果显示流域中林业用地面积从 1990年的 6 4 9%增长到 1998年的6 6 4 % ,但是森林有林地 (郁闭度 >30 %的天然林和人工林 )从 1990年的 5 2 6 %减少到 1998年的 35 3%。并且分析大规模商业性森林砍伐、基础建设、经济作物的种植、刀耕火种、薪材过度采集和砍伐建筑用材等引起了森林的结构的显著变化和退化 ,从而导致了生物多样性的下降。  相似文献   

20.
Communities can change gradually or abruptly, and directionally (to an alternate state) or non-directionally. We briefly review the history of theoretical and empirical perspectives on community change, and propose a new framework for viewing temporal trajectories of communities in multivariate space. We used a stream fish dataset spanning 40 years (1969–2008) in southern Oklahoma, USA, emphasizing our own 1981–2008 collections which included well-documented, extreme drought and flood events, to assess dynamics of and environmental factors affecting the fish community. We evaluated the trajectory of the Brier Creek community in multivariate space relative to trajectories in 27 published studies, and for Brier Creek fish, tested hypotheses about gradual versus event-driven changes and persistence of shifts to alternate states. Most species were persistent, qualitatively, across the four decades, but varied widely in abundance, with some having unusually strong reproduction after extreme droughts. The community had an early period of relatively gradual and directional change, but greater displacement than predicted at random after two consecutive extreme droughts midway through the study (1998 and 2000). But, the community subsequently returned toward its former state in the last decade. This fish community is characterized by species that are tolerant of environmental extremes, and have life history traits that facilitate population recovery. The community appears “loosely stable” about a long-term average condition, but the impacts of the two consecutive droughts were substantial, and may foretell future dynamics of this or other communities in a changed global climate if disturbance events become more frequent or severe.  相似文献   

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