Using NDVI to Assess Vegetative Land Cover Change in Central Puget Sound

We used the Normalized Difference Vegetation Index (NDVI) in the rapidly growing Puget Sound region over three 5-year time blocks between 1986–1999 at three spatial scales in 42 Watershed Administrative Units (WAUs) to assess changes in the amounts and patterns of green vegetation. On average, approximately 20% of the area in each WAU experienced significant NDVI change over each 5-year time block. Cumulative NDVI change over 15 years (summing change over each 5-year time block) was an average of approximately 60% of each WAU, but was as high as 100% in some. At the regional scale, seasonal weather patterns and green-up from logging were the primary drivers of observed increases in NDVI values. At the WAU scale, anthropogenic factors were important drivers of both positive and negative NDVI change. For example, population density was highly correlated with negative NDVI change over 15 years (r = 0.66, P < 0.01), as was road density (r = 0.71, P < 0.01). At the smallest scale (within 3 case study WAUs) land use differences such as preserving versus harvesting forest lands drove vegetation change. We conclude that large areas within most watersheds are continually and heavily impacted by the high levels of human use and development over short time periods. Our results indicate that varying patterns and processes can be detected at multiple scales using changes in NDVIa values.     

Mapping Invasive Aquatic Vegetation in the Sacramento-San Joaquin Delta using Hyperspectral Imagery

The ecological and economic impacts associated with invasive species are of critical concern to land managers. The ability to map the extent and severity of invasions would be a valuable contribution to management decisions relating to control and monitoring efforts. We investigated the use of hyperspectral imagery for mapping invasive aquatic plant species in the Sacramento-San Joaquin Delta in the Central Valley of California, at two spatial scales. Sixty-four flightlines of HyMap hyperspectral imagery were acquired over the study region covering an area of 2,139 km² and field work was conducted to acquire GPS locations of target invasive species. We used spectral mixture analysis to classify two target invasive species; Brazilian waterweed (Egeria densa), a submerged invasive, and water hyacinth (Eichhornia crassipes), a floating emergent invasive. At the relatively fine spatial scale for five sites within the Delta (average size 51 ha) average classification accuracies were 93% for Brazilian waterweed and 73% for water hyacinth. However, at the coarser, Delta-wide scale (177,000 ha) these accuracy results were 29% for Brazilian waterweed and 65% for water hyacinth. The difference in accuracy is likely accounted for by the broad range in water turbidity and tide heights encountered across the Delta. These findings illustrate that hyperspectral imagery is a promising tool for discriminating target invasive species within the Sacramento-San Joaquin Delta waterways although more work is needed to develop classification tools that function under changing environmental conditions.     

基于GIS的黄土高原植被生态信息系统研究

利用地理信息系统(GIS)技术在黄土高原地区植被与环境关系研究中开展了植被生态信息系统方面的应用研究,分析了植被生态信息系统的技术特征,并对建立黄土高原地区植被生态信息系统的一些问题进行了探讨,为西部大开发提供科学依据。     

秭归县植被结构演变及土壤侵蚀评价

为详细了解水库建设期秭归县植被结构演变及土壤侵蚀风险情况,使用TM和SPOT等中高分辨率遥感数据获取的秭归县1992、2007年1〖DK〗∶50 000土地利用分类、植被覆盖度、土壤侵蚀风险及1999～2007年SPOT VEGETATION NDVI等。利用景观格局方法研究植被景观格局演变,分析植被结构与土壤侵蚀风险变化特点。结果表明：1992～2007年,植被景观格局更加破碎,斑块离散程度变大,多样性提高,乔、灌等仍是优势类型,受不同人类政策的影响,不同类型植被类型景观特征响应表现出差异性。植被覆盖度得到改善,其中秭归中南部植被水平密度结构得到明显改善,对降低土壤侵蚀风险起到了积极作用。水库周边地区作为人类活动扰动的集中区,水土保持任务依然艰巨。通过遥感和GIS手段分析区域土地景观格局演变及其生态环境效应,分析变化背后的驱动机制和限制因素,甄别人类活动影响力,为研究三峡人地关系和谐发展提供借鉴和参考     

三峡水库156米蓄水位消落区植被恢复遥感动态监测研究

基于2007～2009年的Landsat5 TM、HJ 1A/1B CCD遥感数据,利用像元二分法对三峡水库156 m蓄水位消落区的植被覆盖度进行了计算,分析了消落区植被恢复的时空变化特征,探讨了植被恢复时空变化的影响因子。2007、2008、2009年3 a 156 m蓄水位消落区植被覆盖度分别为512%、515%、492%,其中支流消落区的植被覆盖度高于干流,这与地形条件有关,坡度的大小决定了消落区植被覆盖的空间差异。2008年与2007年消落区植被覆盖状况基本一致,而2009年的植被覆盖度低于之前两年,这与三峡大坝水位调度方案不同有关,退水较晚时,植被生长时间较短,其植被覆盖度较低。研究结果表明,在正常的调度、一定的地形条件下,淹没数月的消落区植被具有一定的自然萌生能力。     

两种植被指数与地表温度定量关系的比较研究——以南京市为例

加强绿化可有效缓解城市热岛（UHI）效应,但植被降温规律如何,如何科学绿化一直模糊不清。以南京市ETM+影像为数据源,经ATCOR2模块大气校正后,提取了南京城区地表温度（LST）、归一化植被指数（NDVI）和减化比值植被指数（RSR）,基于实测值和同时相ASTER数据反演结果的双重验证,拟合了两种植被指数与地表温度的定量关系,并进行了对比研究。结果表明：南京市存在明显的UHI,城区水体和绿地为显著的低温区,除水体外,植被覆盖度高的区域地表温度明显低于植被稀少或无植被区;地表温度与NDVI呈显著线性负相关,与RSR呈显著幂函数负相关,后者的相关性高于前者;以〖WTBX〗RSR〖WTBZ〗=32为界,此值之前,地表温度随着植被覆盖增加而锐减,此值之后,植被覆盖继续增加,地表温度却趋于恒定,呈现植被降温效应“饱和”现象;RSR能直接说明对于不同下垫面,增加相同的植被覆盖度其降温效果存在差异,而不进行土地利用分类,NDVI无法揭示此现象     

退化山地植被恢复和重建的基本理论和方法

退化植被恢复和重建已成为我国农村社会经济环境持续发展面临的迫切任务,提出了人工恢复和退建退化山地植被的基本方法论。退化山地植被和重建必需以兼顾退化 治理和农村经济发展,建设生态经济型植被为目标,阐述了在恢复和重建过程中应的九项生态学原理和芾项技术方法,介绍了诊断一玫方案一物种选择－各种植物 群的设计及其组合与实施－监测和进一步优化调控等基本人工恢复和重建退化地山植被的步骤。该方法论已在岷江上游的在     

铜陵铜尾矿复垦现状及植物在铜尾矿上的定居

安徽省铜陵市位于长江中游,是我国主要的铜矿产区,其铜尾矿共有5个主要的分布区域。随排放时间的延长,各尾矿库的持水保肥能力和植被覆盖率提高;铜尾矿限制植物定居的主要因素是极端贫瘠和重金属毒性,各尾矿库的重金属含量都很高,而N 、P、K和有机质的含量很低甚至为零。自然和人工定居于尾矿上的植物共有9 科37 属40种,其中禾本科、豆科、菊科植物占所有植物种的72.5%,此3科植物因有完美的生态适应机制而能成为在尾矿上定居的先锋植物和优势种。铜尾矿库植被自然演替属于几十年甚至上百年的长期演替,铜矿废弃地的治理和恢复重建更是一项长期而艰巨的工作。     

南水北调中线水源地不同植被类型坡地土壤水分特征研究——以秦岭南坡宁陕县寨沟小流域为例

为了解不同植被类型土壤水资源的变化规律,选择南水北调中线水源区宁陕县寨沟区域典型植被针阔混交林、针叶林、板栗林、灌木林、荒坡草地和坡耕地为研究对象,通过样地调查与实验分析的方法对其土壤水分物理特征及有机质含量进行测定研究.结果表明,各种有林地的土壤容重、孔隙度和有机质等理化特征均优于荒坡和坡耕地;针阔混交林土壤含水量最高,蓄水能力明显好于其它植被类型;在垂直剖面上,各种植被类型坡地土壤含水量和饱和蓄水量随土壤深度的增加基本呈递减趋势,但有林地下降幅度较大,表层含水量明显高于荒坡与坡耕地表层.由此可见,在涵养水源方面,针阔混交林最好,针叶林、板栗林与灌木林次之,荒坡与坡耕地较差.     

城市河涌污染治理技术的研究进展

随着经济的高速发展,大量污染物排放于城市河涌,导致城市河涌受到严重的污染。采取有效的技术措施治理河涌污染势在必行。结合近年来国内外河涌治理的研究成果,综述了河涌治理的主要技术的原理、特点、存在的问题,并指出目前各项技术的研究重点。