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941.
942.
近15年来长江源区土地利用变化及其生态环境效应 总被引:14,自引:3,他引:11
潘竟虎 《长江流域资源与环境》2005,14(3):310-315
长江源区是我国重要的水源涵养区,也是高海拔地区生物多样性最集中的地区和生态变化最为敏感的地区。基于1986年TM和2000年ETM+卫星遥感数据和野外实地调查,采用GIS软件和景观生态空间分布格局分析方法,对长江源区近15年来土地利用类型的时空变化进行了研究。结果表明:1986~2000年,源区林地和湿地面积减少54.2 %和42.69 %,建设用地、耕地和未利用土地面积分别增加120 %、43.83 %和21.1 %。全区土地利用的空间位置转换面积大于其数量变化,土地利用类型总变化的面积大小依次是草地>未利用土地>湿地>水域>林地>耕地>建设用地。土地利用动态转化过程以草地转化为未利用土地、湿地转化为草地和未利用地逆转为草地为主要特征。15年里景观破碎化程度加剧,分维数和多样性指数增加,优势度降低,景观异质性增强。长江源区脆弱的生态体系对土地利用变化响应强烈,造成水土流失与沙漠化程度加剧,导致大范围高寒草甸、草原植被退化,湿地萎缩。气候变化和人类经济活动是导致研究区土地利用变化的主要因素。 相似文献
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The Cerrado is one of the most threatened biomes in South America. To create protection actions on any scale, understanding drivers and consequences of land cover and land use (LC and LU) is essential. This study defines the composition and configuration of a Cerrado landscape watershed from 1975 to 2011. Using Landsat images and socioeconomic census data, we determined the forces acting on LC and LU change processes and their consequences. LC classes differ from LU classes for landscape dominance and processes. Economic opportunities drove LU change and its spatial distribution was related to soil, streams, and roads. Deforestation was the main cause of forest loss but forest degradation was also important, with both presenting different patterns. The spatial distribution of bare soil was related to pasture in degradation and streams. Bare soil distribution was related to pasture in degradation and streams. We concluded that broad scale factors drove changes, but local features determined distribution, and that watershed conservation plans should act on different scales, with management being spatially explicit. 相似文献
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IntroductionA pedestrian crash occurs due to a series of contributing factors taking effect in an antecedent-consequent order. One specific type of antecedent-consequent order is called a crash causation pattern. Understanding crash causation patterns is important for clarifying the complicated growth of a pedestrian crash, which ultimately helps recommend corresponding countermeasures. However, previous studies lack an in-depth investigation of pedestrian crash cases, and are insufficient to propose a representative picture of causation patterns. Method: In this study, pedestrian crash causation patterns were discerned by using the Driving Reliability and Error Analysis Method (DREAM). One hundred and forty-two pedestrian crashes were investigated, and five pedestrian pre-crash scenarios were extracted. Then, the crash causation patterns in each pre-crash scenario were analyzed; and finally, six distinct patterns were identified. Accordingly, 17 typical situations corresponding to these causation patterns were specified as well. Results: Among these patterns, the pattern related to distracted driving and the pattern related to an unexpected change of pedestrian trajectory contributed to a large portion of the total crashes (i.e., 27% and 24%, respectively). Other patterns also played an important role in inducing a pedestrian crash; these patterns include the pattern related to an obstructed line of sight caused by outside objects (9%), the pattern that involves reduced visibility (13%), and the pattern related to an improper estimation of the gap distance between the vehicle and the pedestrian (10%). The results further demonstrated the inter-heterogeneity of a crash causation pattern, as well as the intra-heterogeneity of pattern features between different pedestrian pre-crash scenarios. Conclusions and practical applications: Essentially, a crash causation pattern might involve different contributing factors by nature or dependent on specific scenarios. Finally, this study proposed suggestions for roadway facility design, roadway safety education and pedestrian crash prevention system development. 相似文献
948.
Elena Cantarello Adrian C. NewtonRoss A. Hill Natalia Tejedor-GaravitoGuadalupe Williams-Linera Fabiola López-BarreraRobert H. Manson Duncan J. Golicher 《Ecological modelling》2011,222(5):1112-1128
Examining the potential for ecological restoration is important in areas where anthropogenic disturbance has degraded forest landscapes. However, the conditions under which restoration of degraded tropical dry forests (TDF) might be achieved in practice have not been determined in detail. In this study, we used LANDIS-II, a spatially explicit model of forest dynamics, to assess the potential for passive restoration of TDF through natural regeneration. The model was applied to two Mexican landscapes under six different disturbance regimes, focusing on the impact of fire and cattle grazing on forest cover, structure and composition. Model results identified two main findings. First, tropical dry forests are more resilient to anthropogenic disturbance than expected. Results suggested that under both a scenario of small, infrequent fires and a scenario of large, frequent fires, forest area can increase relatively rapidly. However, forest structure and composition differed markedly between these scenarios. After 400 years, the landscape becomes increasingly occupied by relatively shade-tolerant species under small, infrequent fires, but only species with both relatively high shade tolerance and high fire tolerance can thrive under conditions with large, frequent fires. Second, we demonstrated that different forms of disturbance can interact in unexpected ways. Our projections revealed that when grazing acts in combination with fire, forest cover, structure and composition vary dramatically depending on the frequency and extent of the fires. Results indicated that grazing and fire have a synergistic effect causing a reduction in forest cover greater than the sum of their individual effects. This suggests that passive landscape-scale restoration of TDF is achievable in both Mexican study areas only if grazing is reduced, and fires are carefully managed to reduce their frequency and intensity. 相似文献
949.
天宝岩自然保护区森林景观格局与环境关系的尺度效应分析 总被引:5,自引:0,他引:5
为揭示景观格局内演机制,在3S技术平台支撑下,借助TM遥感像图、植被分类图和二类调查数据,并引入CCA(Canonical Correspondence Analysis)排序方法,对天宝岩森林景观格局与环境的关系及其尺度效应进行定量分析.结果表明:随着取样尺度的递减,排序轴各特征值之和呈增大趋势,依次为:3.137、3.349、3.484、4.660及4.848;而累积景观–环境解释量和景观–环境相关系数皆呈先增后减的趋势,分别在scale3和scale2达到最大;景观类型分布呈现较为明显的纬度梯度变化规律(纬度与第一轴的相关系数:-0.2019~-0.3789)和垂直分布规律(海拔与第一轴的相关系数:-0.3218~-0.4760),其中沿纬度梯度上分布的景观类型依次为:竹林、落叶阔叶林、针阔混交林、农田、常绿阔叶林、山顶矮曲林、常绿针叶林、泥潭藓沼泽、灌草丛;在较低海拔上分布的景观类型主要有竹林和农田,在较高海拔上分布着泥潭藓沼泽、灌草丛和山顶矮曲林;景观格局与环境关系具有尺度效应,环境因子对景观格局分布的影响程度随着尺度的变化而变化.图2表2参36 相似文献
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人工林赤腹松鼠危害的空间分布格局 总被引:1,自引:0,他引:1
2009年8月和12月,采用样方调查法,对四川省洪雅县柳杉(Crypotomeria fortunei)和杉木(Cunninghami lanceolata)人工混交林的赤腹松鼠(Callosciurus erythraeus)危害进行了调查和分析.共调查了142个10 m×10 m的样方,采用坐标记录法,记录样方内每株林木的坐标值、树种、胸径、冠幅、株下草本盖度、树冠交叠度、是否邻近林窗及其它非生物生境因子(小路、公路、溪水、悬崖)、受害(2 mo以内,以痕迹开始发黑区分)程度共9个参数,共收集3 560株林木数据.分别采用方差均值法和最近邻体法对受害株在研究区和样方尺度上的空间格局进行分析,并在样方尺度上探究植株受害程度与生境因子的关系.结果显示,在研究区尺度上赤腹松鼠危害呈聚集分布,在样方尺度上则以随机分布为主.植株受害程度与其株下草本盖度呈正相关(P=0.007),与树冠交叠度也呈现出正相关(P=0.029),而与其它因子没有显著性的相关性(P>0.05).因此认为赤腹松鼠对人工林林木的危害在研究区尺度上是与其生活环境需求相关的,如食物资源、隐蔽条件等;在对林木株的危害选择上则是随机的,但林木株受害的程度与其株下的草本盖度和树冠的交叠度呈现出显著的正相关关系.图2表5参30 相似文献