基于SPOT—VGT的黄河流域植被覆盖时空演变

植被是土地覆盖中的最主要部分,是连接土壤、大气和生物等要素的自然“纽带”。植被覆盖动态变化对全球能量循环和物质循环具有重要影响,是全球变化研究的重要内容之一。黄河流域作为我国重要的粮食生产基地,其环境变化直接影响到流域经济的可持续发展。为了快速准确地提取地表植被状况,了解黄河流域生态环境,利用1998—2011年的SPOT-VGT遥感数据,结合地理信息技术,采用均值法和趋势分析法对黄河流域植被NDVI时空分布特征和变化趋势进行了动态监测。结果表明,（1）黄河流域14年NDVI均值的空间分布整体特征是东南部平原、盆地和西部山地植被状况要好于北部地区。其次,黄河流域属于干旱半干旱地区,植被发育主要依赖于水文条件,所以沿黄河干流和支流区域也具有较高的植被NDVI值。（2）黄河流域植被NDVl年均值近14年间整体呈缓慢增长趋势,1998--2000年呈现急剧减少态势,2001--2003年出现了较为快速的增长,2004--2011年又出现了较长时间的连续增长过程。（3）黄河流域植被NDVI基本不变的区域约占研究区总面积的71．13％;植被NDVI轻微改善的区域约占流域总面积的27．30％,且主要分布于流域东南部的盆地、平原和西部的山地、丘陵地区,植被NDVI退化的区域面积约占流域总面积的0．98％。黄河流域自1998年以来,植被NDVI整体在不断提高,生态环境在不断改善。     

1982—2006年京津冀地区植被时空变化及其与降水和地面气温的联系

利用NOAA/AVHRR归一化植被指数（Normalized difference vegetation index,NDVI）,分析过去25年（1982—2006年）京津冀地区生长季（4—10月）植被覆盖时空变化、趋势及其与降水和地面气温的联系。经验正交函数展开（EOF）、奇异值分解（SVD）及相关分析,结果表明：过去25年京津冀地区植被总体呈增加趋势,其中,河北中部地区增长速率超过3%/10 a。植被覆盖年际变化与气温变化呈正相关,但与降水变化的正相关更加显著。1989年和1999—2002年的干旱导致当年NDVI显著减少,而1990、1998年和2003—2005年降水增加使得研究区NDVI明显增加。     

气候因子与植被的时滞相关分析——以广西为例

广西地区地下河发育,地表水缺乏,生态系统脆弱、抗干扰能力低,灾害频繁,森林生态系统严重退化,石漠化程度加剧,属于生态脆弱区域,而植被变化是生态系统对气候变化响应的指示器,其变化研究对该地区生态环境建设具有重要意义。文章基于1999--2010年气温与降水数据和GIMMS．NDVI（GlaobalInventoryModellingandMappingMtudies-NormalDifferenceVegetionIndex）数据集,研究近12年来广西地区植被覆盖时空特征。通过时滞相关分析法,分析研究区不同植被类型受气温和降水的影响,即植被NDVI对气温和降水的响应程度。结果表明,（1）植被NDVI与温度的时滞相关程度强于降水,而响应时间刚好相反,植被NDVI对降水的响应比对温度的响应程度要快。（2）植被NDvI与降水的时滞相关规律呈桂南较弱—桂中较强—桂北较弱,但响应时间刚好相反,即桂南较快一桂中较慢—桂北较快。（3）植被NDvI与温度的时滞相关性变化规律呈由南向北递减,响应时间由南向北变快。（4）植被NDVI与气候因子时滞相关越强,响应的时间就越迟缓,反之越快。（5）不同的植被类型对水热条件响应程度不同,与水热条件时滞相关越强的植被则滞后时间相对越久。     

基于MODIS的山东省植被覆盖时空变化及其原因分析

卫星遥感获取的归一化植被指数(NDVI)可以指示地表绿度和植被覆盖特征,被广泛应用于大尺度地表植被活动的监测和评估。基于2000─2014年的328景MODIS/NDVI时间序列数据,采用基于栅格像元的趋势分析和稳定性分析方法,深入分析了2000年以来山东省不同区域植被覆盖和绿度变化特征。结果表明,(1)近15年山东省植被年平均NDVI和春季NDVI都呈现显著增加趋势(P0.01),NDVI的增加趋势与降水量的年际变化关系显著(P0.05);由于城市化进程加剧,生长季绿色植被面积显著减少,平均每年减少243 km~2。(2)NDVI变化趋势具有明显的空间差异,鲁西农业区植被与黄河三角洲以及南四湖的湿地植被变化趋势相反,农田植被绿度有增加趋势,湿地植被绿度下降明显。这一趋势差异与不同植被类型对于降水年际变化的响应差异有关。(3)由于不同植被类型对于自然和人为活动干扰的适应能力不同,不同地区的植被覆盖在时间序列上表现出不同的稳定性。植被稳定性的排序为:农田植被森林灌木植被湿地植被。说明湿地植被对于环境变化的响应最敏感,而人为管理的农田植被的抗干扰能力最强。本研究对于了解山东省植被覆盖变化格局特征和评估不同生态系统的气候变化响应具有积极作用。     

西南喀斯特地区植被变化及其与气候因子关系研究

受气候变化和退耕还林还草工程实施的影响,植被分布产生一定的变化,厘清气候因子与植被生长的关系,可以为生态维护与治理提供参考依据,为生态保护成效评估提供科学基础。选择环江喀斯特区,以中分辨率卫星成像光谱仪(MODIS)卫星遥感250m空间分辨率植被指数NDVI,分析2000-2017年该地区植被变化趋势,利用多元线性回归分析累积降水、温度、辐射等气候因子的影响范围和程度,以残差趋势法厘定植被变化中的人为贡献。结果表明,(1)2000-2017年,环江地区87%的地区植被年均NDVI呈现不同程度的增加趋势,增长率为0.4%a~(-1);主要植被类型农田、森林、草地年均NDVI持续改善,其中森林的改善状况最好。(2)环江地区气候变化整体呈冷湿化。温度、累积降水、辐射对植被年均NDVI的影响情况不同,就环江地区而言,温度、辐射对年均NDVI表现出正影响,且温度影响最大;累积降水与年均NDVI呈负相关。(3)不同植被类型受气候因素的影响不同,在气候因素对植被年均NDVI的解释度较高的地区,农田主要受温度影响,森林和草地主要受辐射和温度的共同影响。(4)环江地区气候因素可以解释8.5%的年均NDVI的变化情况。(5)环江地区除气候因素以外的其他因素对NDVI影响更大。     

基于SPOT-VGT的黄河流域植被覆盖时空演变

植被是土地覆盖中的最主要部分,是连接土壤、大气和生物等要素的自然"纽带"。植被覆盖动态变化对全球能量循环和物质循环具有重要影响,是全球变化研究的重要内容之一。黄河流域作为我国重要的粮食生产基地,其环境变化直接影响到流域经济的可持续发展。为了快速准确地提取地表植被状况,了解黄河流域生态环境,利用1998—2011年的SPOT-VGT遥感数据,结合地理信息技术,采用均值法和趋势分析法对黄河流域植被NDVI时空分布特征和变化趋势进行了动态监测。结果表明,(1)黄河流域14年NDVI均值的空间分布整体特征是东南部平原、盆地和西部山地植被状况要好于北部地区。其次,黄河流域属于干旱半干旱地区,植被发育主要依赖于水文条件,所以沿黄河干流和支流区域也具有较高的植被NDVI值。(2)黄河流域植被NDVI年均值近14年间整体呈缓慢增长趋势,1998—2000年呈现急剧减少态势,2001—2003年出现了较为快速的增长,2004—2011年又出现了较长时间的连续增长过程。(3)黄河流域植被NDVI基本不变的区域约占研究区总面积的71.13%;植被NDVI轻微改善的区域约占流域总面积的27.30%,且主要分布于流域东南部的盆地、平原和西部的山地、丘陵地区,植被NDVI退化的区域面积约占流域总面积的0.98%。黄河流域自1998年以来,植被NDVI整体在不断提高,生态环境在不断改善。     

近代黄河三角洲植被覆盖度时空变化分析

为了深化研究近代黄河三角洲植被演化规律与机理,指导该地区合理开发和保护植被资源,选用Landsat等卫星遥感数据结合野外调查数据,利用像元二分模型估算并分析了该地区1986—2015年长时间序列植被覆盖度时空变化过程及影响因素(水分条件、盐分条件、人类活动)。结果表明,该地区近30年植被覆盖度时空变化明显,(1)空间变化上,植被覆盖度呈现由西南向东北递减,由河流两岸向沿海递减的趋势,并且随着时间变化,这两种趋势越来越明显。随着人类活动加强,植被覆盖破碎化显著。(2)时间变化上,1986—2015年该地区植被覆盖度总体呈上升趋势,由1986年的36.77%上升为2015年的37.83%。中高、高植被覆盖面积增幅最大,达到314.96 km~2。低植被覆盖度区逐渐转为高植被覆盖度区,特别是2001—2015年,随着研究区生态环境逐渐变化,转化速度逐渐加快。(3)环境因子与植被覆盖度具有一定的相关性,采用基于像元的空间分析法分析不同时滞月降水量与近代黄河三角洲植被覆盖度相关性,发现月降水量与植被覆盖度有较大关系。通过遥感指数构建土壤反演模型,得到盐分空间分布,并进行相关性分析,发现土壤盐分与植被覆盖度相关性系数为-0.331(P0.02),近代黄河三角洲盐碱化对植被生长有一定阻碍作用。人类活动对植被覆盖度的影响主要以农业为主,通过对植被覆盖度与耕地进行相关性分析,得相关性系数为0.452(P0.02),近代黄河三角洲耕地的开发,在一定程度上促进了该地区植被覆盖度的恢复。     

基于MODIS数据的珠三角地区NDVI时空变化特征及对气象因素的响应

珠江三角洲是广东省经济密度最大、人为活动最强烈的区域,随着工业化和城市化的迅速发展,该区域出现了各种生态环境问题。通过对2001-2017年覆盖珠三角地区的MODIS/NDVI数据进行月时间序列重构和年时间序列合成,利用趋势分析方法和空间自相关分析方法对珠三角地区NDVI的时间变化趋势和空间格局特征进行研究,同时结合气象站点观测资料,基于相关系数方法分析NDVI对气象因素的响应。结果表明,(1)在过去的17年中,珠三角地区NDVI在年际变化上呈现波动增长趋势,总体年平均增长速率为0.005 1。(2)在空间分布上,珠三角范围内有90.84%区域的植被呈增长趋势,而在珠三角核心地带的城市群集区域存在植被退化现象,占全区面积的9.16%。(3)珠三角地区NDVI具有高空间集聚特性,受地形和城区分布影响,低植被覆盖集聚区和高植被覆盖集聚区分布格局显著且变化稳定,在多年平均NDVI的局部空间自相关分析中分别占全区面积的28.77%和33.69%。(4)珠三角地区NDVI和气温、降水及日照时数在月变化上显著相关,NDVI对气温和降水的响应分别存在1个月和1-2个月的滞后效应,并且这种滞后效应在空间分布上也体现出"西南-东北"方向的区域差异,而NDVI对日照时数的响应不存在滞后。(5)在年尺度上,珠三角地区NDVI与气象因素之间的相关性不显著。研究结果对珠三角地区恢复植被和修复生态具有重要的参考价值和现实意义     

中国不同植被覆盖类型NDVI对气温和降水的响应特征

基于1982—2012年植被生长季(4—10月)GIMMS NDVI 3g数据集、中国气象数据网同时期气温与降水月值0.5°×0.5°格点数据集(V 2.0)和MODIS土地覆盖产品,运用GIS和相关统计方法,对中国长时间较为稳定的8种典型植被覆盖类型(常绿阔叶林、落叶阔叶林、混交林、开放灌丛、多树的草原、草原、作物以及作物和自然植被的镶嵌体)NDVI与气温和降水的时空响应特征进行研究。结果表明,除西南部分地区和西北小部分裸地或低植被覆盖地区外,其他地区多年生长季平均NDVI与平均气温呈显著正相关;西藏南部和华南大部分地区植被NDVI与降水呈负相关,强降水会对植物生长产生一定阻碍作用,其他地区多年生长季平均NDVI与平均降水呈显著正相关;从植被覆盖类型上看,除常绿阔叶林和多树的草原外,其他植被覆盖类型与气温、降水均呈正相关关系,其中落叶阔叶林、开放灌丛和草原与气温和降水均呈较高的正相关,且对气温的响应比对降水强烈;NDVI对气温和降水的响应具有空间异质性,不同植被覆盖类型NDVI与气温和降水的相关性不同,相同植被覆盖类型NDVI在不同地区的相关性也不同,分布在西南地区的常绿阔叶林NDVI与气温呈正相关,而分布在华南、台湾地区的常绿阔叶林NDVI与气温呈负相关,暖湿西南季风可能是造成差异的原因;植被NDVI对气温、降水的响应存在时滞效应,对降水的时滞效应更为显著,不同植被覆盖类型NDVI对气温和降水的滞后期不同,在生长季末期,落叶阔叶林NDVI对气温的响应滞后期约为1个月,西南开放灌丛和华北草原带NDVI对降水的响应滞后期为1—2个月。研究结果可为中国陆地生态环境建设及保护提供理论依据。     

三江源地区基于植被生长季的NDVI对气候因子响应的差异性研究

采用1999—2008年NDVI和三江源地区及周边31个气象站点的温度和降水旬数据,在确定每年5月中旬至9月底作为三江源地区植被生长季（14旬）的基础上,分析NDVI对气候因子变化响应的区域差异。结果显示：以巴颜喀拉山为界,三江源西部生长季内NDVI指数对温度、降水的线性相关性明显比中东部普遍,同时,不同海拔地段响应程度存在着明显的差异,且海拔5300m左右为线性响应的最高限,NDVI对气候因子的线性响应主要表现为对温度正相关和降水负相关。因此,对三江源生长季内植被生长而言,水条件明显好于温度条件,并且温度对植被覆盖的影响通过直接正相关和降水负相关表现出来,温度是三江源地区植被生长的主导因子。     

The impact of grazing on spider communities in a mesophytic calcareous dune grassland

During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished. The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities. Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed and non cattle-grazed sites. Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific habitat structures or inhabiting ant-species.     

Post-fire vegetation regrowth detection in the Deiva Marina region (Liguria-Italy) using Landsat TM and ETM+ data

Obtaining quantitative information about the recovery of fire-affected ecosystems is of utmost importance from the management and decision-making point of view. Nowadays the concern about natural environment protection and recovery is much greater than in the past. However, the resources and tools available for its management are still not sufficient. Thus, attention and precision is needed when decisions must be taken. Quantitative estimates on how the vegetation is recovering after a fire can be of help for evaluating the necessity of human intervention on the fire-affected ecosystem, and their importance will grow as the problem of forest fires, climate change and desertification increases.This article performs a comparison of methods to extract quantitative estimates of vegetation cover regrowth with Landsat TM and ETM+ data in an area that burned during the summer of 1998 in the Liguria region (Italy). In order to eliminate possible sources of error, a thorough pre-processing was carried out, including a careful geometric correction (reaching RMSE lower than 0.3 pixels), a topographic correction by means of a constrained Minnaert model and a combination of absolute and relative atmospheric correction methods. Pseudo Invariant Features (PIF) were identified by implementing an automated selection method based in temporal Principal Component Analysis (PCA), which has been called multi-Temporal n-Dimensional Principal Component Analysis (mT-nD-PCA).Spectral Mixture Analysis (SMA) was compared against quantitative vegetation indices which are based on well known traditional vegetation indices like Normalized Difference Vegetation Index (NDVI) and Modified Soil Adjusted Vegetation Index (MSAVI). Accuracy assessment was performed by regressing vegetation cover results obtained with each method against field data gathered during the fieldwork campaign carried out in the study area. Results obtained showed how vegetation cover fractions extracted from the NDVI based quantitative index were the most accurate, being superior to the rest of the techniques applied, including SMA.     

The impact of grazing on spider communities in a mesophytic calcareous dune grassland

During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished. The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities. Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed and non cattle-grazed sites. Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific habitat structures or inhabiting ant-species. Nomenclature: Roberts (1987, 1995) forAraneae; van der Meijden et al. (1990) for vascular plants; Corly et al. (1981) for bryophytes; Schaminée et al. (1996) for vegetation associations.     

沙地退化植被恢复过程中植被的空间异质性

通过野外取样和室内分析,应用地统计学分析方法研究了科尔沁沙地退化植被恢复过程中不同封育年限（0、11和20年）的流动沙丘的植被盖度和丰富度特征及其空间异质性规律。结果表明,随着流动沙丘的固定和封育年限的增加,植被盖度和丰富度逐渐增加。在流动沙丘植被恢复过程中,植被盖度和丰富度具有明显的空间自相关性,其空间自相关范围从封育0年的流动沙丘（46.05m和33.63m）、封育11的流动沙丘（21.63m和17.25m）到封育20年的流动沙丘（26.12m和24.18m）先减小后增加,但均未超出我们的研究尺度50m,表现出不同大小的斑块形式分布的小尺度分布格局。由半方差函数及其参数和空间分布格局图分析得出,随着沙丘植被的恢复,植被特征的空间异质性在所研究的尺度上表现出先增大（封育0年到封育11年）后减小（封育11年到封育20年）的变化特点。     

台湾泥岩地区不同刺竹林景观下之土壤与植被变异

台湾西南部泥岩恶地,由于其特殊之土壤,地力流失消耗与区域微气候型态之间的因果循环,在水土保持与景观上形成不易植生绿化的地区及特殊之世界地形。泥岩地区之不同刺林林相之土壤,其林相皆伐后复层植被区土壤性质变异高于其它位置,而其它区之土壤理化性质在时间及空间上之变异不大,可明显区分林相不同之显著差异。不同林相对泥岩地浅层土壤(0~20cm)理化性质的差异,以植物营养元素与植生覆盖因子可充分说明(约占变异范围之62%)。泥岩试区区中移动性物质(交换性钙、钠与镁)明显较少出现在复层林相处区,而易出现于淋洗、冲蚀量较大之刺林相保留区与隔丛择伐区。长效性植物营养元素因子(pH值与有效性磷),因长时间之林相不同,使其较明显趋于复层林相区堆积,并影响地表植生之种类、分布与覆盖情形。0～20cm土壤性质的分布和离子间的移动特性有关,移动性高的钠、镁离子会在冲蚀量高之区域出现,20～40cm土壤性质的分布则和土壤中之母质与植生有关并与因素分析结果相似,其次为可移动性离子的影响,且应用地理统计印证土壤性质在空间之变化,其分布确实与不同林相位置有关,即植生营养元素(pH值、有效性磷)大都朝向复层植被区之趋势。典型相关分析结果,地表覆盖度与入侵植物数量两变量主要系透过第一个典型因素与第二个典型因素而影响到复层植被区之pH值、有机质等土壤理化性质。     

Postfire stand structure in a semiarid savanna: cross-scale challenges estimating biomass.

Algorithms relating remotely sensed woody cover to biomass are often the basis for large-scale inventories of aboveground carbon stocks. However, these algorithms are commonly applied in a generic fashion without consideration of disturbances that might alter vegetation structure. We compared field and remote sensing estimates of woody biomass on savannas with contrasting disturbance (fire) histories and assessed potential errors in estimating woody biomass from cover without considering fire history. Field surveys quantified multilayer cover (MLC) of woody and succulent plants on sites experiencing wildfire in 1989 or 1994 and on nearby unburned (control) sites. Remote sensing estimates of the woody cover fraction (WCF) on burned and control sites were derived from contemporary (2005) dry-season Landsat Thematic Mapper imagery (during a period when herbaceous cover was senescent) using a probabilistic spectral mixture analysis model. Satellite WCF estimates were compared to field MLC assessments and related to aboveground biomass using allometry. Field-based MLC and remotely sensed WCFs both indicated that woody cover was comparable on control areas and areas burned 11-16 years ago. However, biomass was approximately twofold higher on control sites. Canopy cover was a strong predictor of woody biomass on burned and control areas, but fire history significantly altered the linear cover-biomass relationship on control plots to a curvilinear relationship on burned plots. Results suggest predictions of woody biomass from "generic" two-dimensional (2-D) cover algorithms may underestimate biomass in undisturbed stands and overestimate biomass in stands recovering from disturbance. Improving the accuracy of woody-biomass estimates from field and/or remotely sensed cover may therefore require disturbance-specific models or detection of vegetation height and transforming 2-D vegetation cover to 3-D vegetation volume.     

Vegetation cover influence on the morphology and migration patterns of river mouths

The present study focuses on the effects of vegetation cover changes on the dynamic morphology of seven southeastern Mediterranean river mouths. The methodology used comprised monitoring and mapping by GIS techniques, with data derived from historic aerial photographs, which were applied in the investigation of the morphological spatial and temporal migration patterns of the mouths, and subsequent analysis of the vegetation cover changes influencing them. Vegetation cover adjacent to river mouths influences river mouth morphology through five primary mechanisms: a) bank vegetation; b) dune advancement toward the shoreline; c) changes in the beach??s micro-topography; as well as d) long-term continuous channel migration through permanent vegetation patches; and e) channel switching through permanent vegetation patches. The five mechanisms are part of a system of interactions between channel water flow and fluvial processes; coastal sediment transport and coastal processes; and the evolution of plant communities. In the interplay between these factors they all affect and are being affected by one another. In many river mouths artificial channel diversion is often needed due to uncontrolled channel migration. It is demonstrated that vegetation cover can serve as a mean of ??soft?? channel regulation. Therefore, a better understanding of the five influencing mechanisms may aid in controlling and managing river mouth migration patterns. The study contributes to the knowledge about bank vegetation as a tool of ??soft?? channel regulation and thus can contribute to the improvement of coastal zone management.     

Impact of cattle grazing on the occupancy of a cryptic, threatened rail

Impacts of livestock grazing in arid and semiarid environments are often concentrated in and around wetlands where animals congregate for water, cooler temperatures, and green forage. We assessed the impacts of winter-spring (November-May) cattle grazing on marsh vegetation cover and occupancy of a highly secretive marsh bird that relies on dense vegetation cover, the California Black Rail (Laterallus jamaicensis coturniculus), in the northern Sierra Nevada foothills of California, U.S.A. Using detection-nondetection data collected during repeated call playback surveys at grazed vs. ungrazed marshes and a "random changes in occupancy" parameterization of a multi-season occupancy model, we examined relationships between occupancy and habitat covariates, while accounting for imperfect detection. Marsh vegetation cover was significantly lower at grazed marshes than at ungrazed marshes during the grazing season in 2007 but not in 2008. Winter-spring grazing had little effect on Black Rail occupancy at irrigated marshes. However, at nonirrigated marshes fed by natural springs and streams, grazed sites had lower occupancy than ungrazed sites. Black Rail occupancy was positively associated with marsh area, irrigation as a water source, and summer vegetation cover, and negatively associated with marsh isolation. Residual dry matter (RDM), a commonly used metric of grazing intensity, was significantly associated with summer marsh vegetation cover at grazed sites but not spring cover. Direct monitoring of marsh vegetation cover, particularly at natural spring- or stream-fed marshes, is recommended to prevent negative impacts to rails from overgrazing.     

基于RS-GIS的湖北丹江库区土壤水力侵蚀定量分析

湖北丹江库区是南水北调中线工程的主要淹没区和水源区,土壤水力侵蚀是影响水质安全和工程实施的重要因素。以1998年和2003年的TM遥感影像为主要信息源,建立了以植被覆盖度、坡度和土地利用为指标的水力侵蚀遥感分析方法,将水力侵蚀强度分为六级,并结合GIS的空间分析功能对1998年和2003年库区水力侵蚀强度变化及空间分布进行了划分。结果表明五年间库区微度侵蚀、中度侵蚀和强度侵蚀面积呈增加趋势,而轻度侵蚀和极强度侵蚀面积呈减少趋势;并将库区水力侵蚀空间分布划分为北部中低山丘陵中强度侵蚀区和中部河谷城区轻度流失区。分析结果对库区土壤侵蚀的治理和生态环境的改善具有指导意义。