Early human impact in the forest ecotone of southern High Asia (Hindu Kush, Himalaya)     

Georg Miehe  Sabine Miehe  Frank SchlützAuthor vitae 《Quaternary Research》2009,71(3):255-265

The vegetation of the treeline ecotone of the southern declivity of arid High Asia (Hindu Kush, northern areas of Pakistan; Himalaya, northern central Nepal) is dominated by hedgehog-like open dwarf shrublands of thorny cushions. Since climatically sensitive ecotones are always also sensitive to human impact, the question arises whether the current lack of forests is a result of the Subboreal climate decline or of human impact. Due to inadequate knowledge of the pollen flora and of ecological indicator values of the plants, pollen analyses in High Asia have mainly been limited to the regional verification of globally known climatic impulses. However, the role of human impact on regional vegetation patterns has been widely neglected. We postulate that today's open dwarf shrublands replace woodlands and forests. Isolated vigorous juniper trees and successful reforestation appear to confirm our hypothesis. An abrupt decline of Pinus forests before 5700 and 5400 ka cal yr BP can be demonstrated. As the first indicator pollen of human impact appeared at both sites synchronous with the forest pollen decline, we infer human impact to be a more decisive cause for this environment change superimposing the effects of a climatic deterioration. The forests were displaced by open dwarf shrublands.  相似文献   

植被混凝土生态防护技术在高陡边坡上的应用     

席文明 《化工矿产地质》2019,41(1):50-52

针对工程活动形成的高陡边坡,采用植被混凝土生态防护技术进行治理覆绿效果显著。利用植被混凝土生态防护技术,对植被混凝土基材配方及技术指标进行分析,为施工做准备,明确了施工工艺的步骤及注意事项。通过工程实例分析,突显了此技术较高的应用价值及综合效益。  相似文献   

Long‐Term Effects of Natural Enclosure: Carbon Stocks,Sequestration Rates and Potential for Grassland Ecosystems in the Loess Plateau          下载免费PDF全文

Lei Deng  Sandra Sweeney  Zhouping Shangguan 《洁净——土壤、空气、水》2014,42(5):617-625

  相似文献   

The early impact of large wood introduction on the morphology and sediment characteristics of a lowland river     

《Limnologica》2015

Habitat degradation in river ecosystems has considerably increased over the past decades, resulting in detrimental effects on aquatic and riparian communities. During the last two decades, the value of large wood as a resource for river restoration and recovery has been increasingly documented. However, post-project appraisal of the associations between restored large wood, morphological complexity and river ecology as a result of river restoration is extremely rare and thus scientific knowledge is essential. To investigate restored wood-induced morphological response and sediment complexity in an overwidened reach along a low gradient lowland river (River Bure, UK), two sub-reaches containing 12 jams initiated by wood emplacement in 2008 and 2010 and a sub-reach free of wood were studied. Wood surveys recording the dimensions and number of wood pieces in jams, geomorphological mapping of the reach illustrating the spatial distribution of features in and around the jams and in a section free of wood, and sediment sampling (analysed for particle size, organic content and plant propagule abundance) of five recurring patch types surrounding each jam (two wood-related patches and three representing the broader river environment) were performed. Wood jams partially spanned the river channel and contained large pieces of wood that created more open structures than naturally-formed wood jams. Where no wood was introduced, the channel remains wide and the gravel bed is buried by sand and finer sediment. In the restored reaches, fine sediment has accumulated in and around the wood jams and has been stabilised by vegetation colonisation, enhancing flow velocities in the narrowed channel sufficiently to mobilise fine sediment and expose the gravel bed. Sediment analysis reveals sediment fining with time since wood emplacement, largely achieved within the two wood-related patch types. Fine sediment retained around the wood shows a relatively higher plant propagule content than other patch types, suitable for sustaining plant succession as the vegetated side bars aggrade. Although channel narrowing and morphological adjustment has occurred surprisingly rapidly in this low energy, over-widened reach following wood introduction (2–4 years), sustaining the recovery in the longer term to suitably support flora and fauna communities depends on the continued delivery of wood by ensuring a natural supply of sufficiently large wood pieces from riparian trees both upstream and within the reach.  相似文献   

吉林省主要产粮区NDVI时空变化特征     

唐晓玲  任红玲  王杰  刘珂  王颖 《气象与环境学报》2015,31(2):103-107

为了确定作物长势遥感监测的评价指标,利用2000—2012年吉林省EOS/MODIS数据,采用NDVI旬最大值法,结合吉林省主要农作物生长发育的特点,对主要产粮区作物生长季旱田和水田的NDVI时空变化规律进行研究,并分析其与气温和降水的关系。结果表明:2000—2012年吉林省作物生长季农作物的NDVI随作物生长发育进程有明显的变化,水田和旱田两种作物的NDVI时间变化均呈单峰型;吉林省不同区域的NDVI变化趋势一致,5月上旬至6月上旬,NDVI呈缓慢增加的趋势;6月中旬至7月上旬,NDVI迅速增加;7月中旬至8月上旬,NDVI增加缓慢;8月中旬开始,NDVI开始下降。6月中旬开始,吉林省中部地区旱田NDVI明显高于西部地区,NDVI增长速率中部地区大于西部地区,达到峰值的时间中部地区也早于西部地区。吉林省水田NDVI变化中西部地区差异较小,均在8月上旬达到峰值,植被指数时间变化与吉林省作物生长发育进程相吻合。吉林省中西部地区作物的NDVI与气温和降水均呈正相关,气温和降水对NDVI的影响有明显滞后效应,且气温的影响大于降水。  相似文献   

植被变化对西北地区陆气耦合强度的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

赵靖川  刘树华 《地球物理学报》2015,58(1):47-62

西北地区地处欧亚大陆腹地,生态系统对于气候变化和人为影响十分敏感,同时该区也是湿润的东亚季风区与干燥的中亚干旱区的过渡区域,陆气相互作用比较强烈.本文对西北地区植被变化对当地的陆气耦合强度及其与之相关的地表水文过程的影响进行了分析研究,并且找出适于增加植被以缓解西北地区荒漠化趋势的最具成效的地区.本文利用美国国家大气科学研究中心(NCAR,National Center for Atmospheric Research)研制的通用大气模式CAM3(Community Atmosphere Model Version 3)对西北地区植被变化的影响进了数值模拟.本文共设计了三个试验,使用正常地表植被覆盖的参考试验,地表下垫面变为裸土的去植被试验和植被增加的生态环境好转试验.首先,本文对西北地区植被变化对于当地降水量、地表水分盈余量、径流量、地表土壤含水量等地表水文变量的影响进行了分析研究.然后对西北地区植被变化对当地的陆气耦合强度的影响进了分析研究,陆气耦合强度是衡量局地陆气相互作用强弱程度的一个新标准,基于计算年降水量与蒸散量的协方差与降水量方差之比而得到.它利用观测数据或模式输出数据,计算起来简便容易,物理意义明确清晰,陆气相互作用越强烈的地区,其陆气耦合强度也越高.最后,本文计算了一个蒸散-水汽通量散度指数来衡量植被变化对局地蒸散与大气水汽通量散度的影响,其在一定程度上反应了植被变化对局地陆气相互作用和大尺度大气环流输送作用的影响,也可以视为一个评估人为生态环境工程效果的指标.西北地区陆气耦合强度由东南向西北递增.去植被之后,西北地区降水与蒸发普遍减少,其中在东南部区域,地表径流增加约10~40mm,渗流量与地表土壤含水量分别减少约40~80mm和5~20mm3·mm-3,陆气耦合强度上升,这有可能导致水土流失,不利于当地植被的恢复.生态环境好转之后,内陆地区降水与蒸发明显增加,但地表盈余水分有所减少,主要原因是蒸散量相较于降水量增加的更多.其中在沙漠戈壁区边缘的新疆南部与内蒙西部,渗流量与地表土壤含水量分别上升约5~20mm和5~20mm3·mm-3,陆气耦合强度降低,蒸散-水汽通量散度指数较高,这可能主要是由于植被变化对局地陆气相互作用的改变而造成的.植被对于西北地区地表水文过程有着明显的影响,植被的存在能加速西北地区地表水文循环过程,减小陆面蒸散的变化,降低陆气耦合强度.在有限的人力与财力条件下,集中力量在在沙漠戈壁区边缘的新疆南部与内蒙西部适当种植灌木与青草并防止过度放牧,能有效降低当地陆气耦合强度,缓解西北地区荒漠化加剧的趋势.本文下一步还需考虑如模式地表植被数据与真实情况的差异性,海洋因素变化对于植被变化的反馈,以及进行集合实验来增加研究结果的可靠性.  相似文献   

植物物候遥感监测研究进展   总被引：15，自引：2，他引：13       下载免费PDF全文

武永峰  李茂松  宋吉青 《气象与环境学报》2008,24(3):51-58

基于遥感监测方法的植物物候研究已成为全球气候变化研究的一个热点课题,通过对植物物候生长季概念的遥感界定,归纳总结了物候监测的基本原理、遥感数据源以及4种常用的遥感监测方法,并指出各种遥感监测方法存在的问题和不足;以遥感监测技术为支撑,对地区、大洲和全球尺度上物候与气候关系的研究、物候与人类行为关系的研究进行了阐述,指出植物物候的变化常常是二者共同影响的结果。针对当前物候研究中存在的不足,探讨了今后的研究发展方向。  相似文献   

Spatio-temporal Patterns of Vegetation Change in Kazakhstan from 1982 to 2015     

LUO Liang  DU Wenpeng  YAN Huimin  ZHEN Lin  DONG Yu 《资源与生态学报(英文版)》2017,8(4):378-384

The Normalized Difference Vegetation Index (NDVI), as a key indicator of vegetation growth, effectively provides information regarding vegetation growth status. Based on the Global Inventory Monitoring and Modeling System (GIMMS) NDVI time series data for Kazakhstan from 1982 to 2015, we analyzed the spatial pattern and changes in the vegetation growth trend. Results indicated that the three main types of vegetation in Kazakhstan are cropland, grassland and shrubland, and these are distributed from north to south. While the regional distribution pattern is obvious, the vegetation index decreased from north to south. The average NDVI values of the three main vegetation types are in the order of cropland > grassland > shrubland. During the period from 1982 to 2015, the NDVI initially increased (1982-1992), then decreased (1993-2007), and then increased again (2008-2015). The areas where NDVI decreased significantly accounted for 24.0% of the total land area. These areas with vegetation degradation are mainly distributed in the northwest junction between cropland and grassland, and in the cropland along the southern border. The proportions of total grassland, cropland and shrubland areas that were degraded are 23.5%, 48.4% and 13.7%, respectively. Areas with improved vegetation, accounting for 11.8% of the total land area, were mainly distributed in the mid-east cropland area, and the junction between cropland and grassland in the mid-east region.  相似文献   

River Suspended Sediment Control through Riparian Vegetation: A Method to Detect the Functionality of Riparian Vegetation     

Donatella Pavanelli  Claudio Cavazza 《洁净——土壤、空气、水》2010,38(11):1039-1046

The aim of this paper is to propose a method to detect the functionality of riparian vegetation as buffers/filters/trap against soil runoff and polluting agents caused by agricultural land and erosion areas, near the river. The suspended sediment yield (SSY) is the main vector for pollutants and nutrients generated from the runoff, in the Apennines torrents, indeed finer particles of the soil and their aggregates were proved to be the preferential vehicle of nitrogen, phosphorus, and other polluting agents. The stages of the current study were to spot soil erosion critical areas by the application of Universal Soil Loss Equation (USLE), on a river strip buffer of 200 m, with support of aerial photos and satellite images, land surveys, and application of a G. I. S. The riparian vegetation analysis, on a 20 m wide buffer, was obtained on the basis of ecologic richness, the structural quality, and the depth of the vegetation. The two maps obtained, “erosion risk strip” and “degree of effectiveness of riparian vegetation”, were connected to identify, for every river trunk, the level of functionality of the riparian vegetation in relation to the level of risk erosion on the near hill slopes. The methodology was applied on the Gaiana torrent, near Bologna, North Italian Apennines, where both basin soil loss and SSY have been well studies. The proposed methodology has been designed for the control of water pollution induced by suspended solids, pollutants, and nutrients coming from soil erosion and as a tool to improve the quality of the river environment. The method has the advantage of being easily applicable and can represent a basic tool for stakeholders to take decisions regarding the control and improvement of the river and it can suggest ways to improve or replant the degraded vegetation on the stream banks.  相似文献   

Effects of vegetation on flow conveyance and sediment transport capacity   总被引：3，自引：0，他引：3  

Weiming WU  Zhiguo HE Research Assoc. Prof.  National Center for Computational Hydroscience  Engineering  University of Mississippi  University  MS  USA  Postdoctoral Research Assoc.  USA.Present at 《国际泥沙研究》2009,24(3):247-259

In-stream and riparian vegetation may significantly affect flow and sediment transport in vegetated channels. A hydraulic model has been developed in this paper to compute the flow discharge in channels with rigid and flexible vegetation under emergent and submerged conditions. An empirical formula has also been presented to determine the bed-load discharge in vegetated channels. The model has been tested against experimental and field data available in the literature. The computed flow discharge and bed-load transport rate agree well with the measured data.  相似文献