Long-term monitoring of wetlands along the Western-Greek Bird Migration Route using Landsat and ASTER satellite images: Amvrakikos Gulf (Greece)

The west coast of Greece is an important migration route for migratory waterbirds. The wetlands along this coast are important stopover sites during bird migration between wintering and breeding sites. The use of remote sensing methods for mapping bird migration habitats and for temporal monitoring of changes in these habitats was investigated. The Amvrakikos Gulf, a coastal wetland complex along the west coast of Greece, was selected as the study area. Landsat TM and ETM+ images and ASTER VNIR images were used to perform a post-classification change detection over a time period of 15 years (1989–2004). In order to assess the spatial quality of existing wetland patches, spatial metrics (such as patch area, distance between the patches, and proximity) were calculated. To study changes in the degree of fragmentation of the stopover area, a binary patch structure was used in which the focal patches were embedded in a neutral matrix. The results showed that Landsat and ASTER VNIR satellite images can be used to trace small wetlands of approximately 0.5 ha minimum. These data sources are suitable for monitoring changes in wetlands, in particular marshes and mudflats, which are important habitats for migratory waterbirds. In the 15-year period that has been studied there was an estimated 32% decrease in marsh and mudflat area. Among this decrease, 25% went to water surface and 7% to vegetation in the months of August and September. Within the same period of time, a higher degree of fragmentation of the potential bird migration habitat has also been recorded. For this purpose, the remote sensing approach used in this study where change detection is performed on freely available Landsat and ASTER satellite images could be an interesting tool for policy makers and managers, as they allow easy recognition and monitoring of changes in wetlands and therefore contribute to an evaluation of the efficiency of protection and management schemes applied by countries for their wetlands.     

基于土地利用变化的玛纳斯河流域景观生态风险评价

摘要：随着人类活动范围日益扩张和强度增加,景观生态风险评价已经成为预测和衡量生态环境质量和动态演化的重要手段。本文以玛纳斯河流域（简称玛河流域）为研究区,选取2000、2005、2010和2015年4期Landsat TM/ETM遥感影像,运用ENVI软件对研究区土地利用类型进行解译,定量分析流域近15年来土地利用动态变化特征,基于景观格局指数,采用地统计学方法,探究玛河流域景观生态风险程度及时空分异特征。结果表明：（1）2000—2015年,玛河流域景观格局发生了较大变化,耕地景观面积增加最多（2638.31 km^2）,主要由草地和未利用地转入;未利用地景观面积减少最多（2559.99 km^2）,主要转化成了草地、耕地和林地;（2）将流域景观生态风险划分为5个等级,研究期内流域低、中风险区面积增加而较高、高风险区面积减少,整体景观生态风险指数减小,所以研究区生态环境在整体上呈现好转;（3）2000—2005年、2010—2015年玛河流域在景观风险分布格局上发生较小变化,但2005—2010年流域景观风险分布格局发生较大变化,主要是中、较高和高风险区向流域南北方向分散并转移,低风险区向流域北部转移。     

1991-2017年叶尔羌河流域冰川景观格局时空演变

冰川景观变化是全球环境和气候变化的共同"指示器"。随着全球气候变化加剧,干旱和半干旱地区的冰川景观将进一步变化。科学评估冰川景观格局时空演变特征,为应对冰川景观变化及其影响提供科学参考。基于1991-2017年Landsat TM/ETM+/OLI遥感影像,采用监督分类方法获取叶尔羌河流域冰川景观时空格局及变化数据,利用景观格局指数、质心迁移模型、分形维数等方法分析近26年叶尔羌河流域冰川景观格局时空演变特征。结果表明：（1）1991-2017年叶尔羌河流域冰川斑块面积呈消减趋势,但有所减缓,共减少799.50 km²（-13.09%）。冰川斑块面积消减主要集中在海拔5400-5800 m之间,相较之下,海拔4400 m以下的区域冰川斑块面积消减率最高,达63.68%;不同坡度冰川景观消减率存在差异,陡坡冰川斑块面积消减率最高（15.98%）,急陡坡消减率最低（2.87%）;阴阳两坡冰川景观均呈消减趋势,阳坡冰川斑块面积消减速率显著高于阴坡。（2）近26年来,叶尔羌河流域冰川斑块数量、最大斑块指数均减小,而平均形状指数、平均周长面积比、分裂指数均增加,表明冰川景观不断消减,破碎化程度增加。（3）研究期间,叶尔羌河流域冰川景观质心发生迁移,整体呈现东北偏移趋势。（4）通过分形理论对叶尔羌河流域冰川景观空间结构特征进行分析表明,该流域冰川景观消减率略微降低,但仍然处于持续消融状态。     

Application of remote sensing to site characterisation and environmental change analysis of North African coastal lagoons

This article describes the use of satellite imagery for identifying key environmental characteristics within three North African coastal lagoons (Merja Zerga, Morocco; Ghar El Melh, Tunisia and Lake Manzala, Egypt) and for detecting the major environmental changes within these environments. A combination of Landsat MSS, Landsat TM, Landsat ETM+ and ASTER imagery was acquired for the three sites for a period covering the last three decades (1972–2004). Following geometric correction and enhancement, the interpretation of the most recent image acquired for each of the three lagoons provides important insights into their current conditions. For Merja Zerga, these include the distribution of the largest channels which drain extensive inter-tidal mudflats and the two major depositional features associated with sources of freshwater. The distribution of marginal aquatic vegetation is highlighted as is the intensive use of the surrounding landscape for agriculture. Intensive agriculture around Ghar El Melh is also indicated. The influence of the Mejerda River, which was diverted away from the lagoon over 100 years ago, is shown to persist as a residual area of deltaic deposits in shallow water that has been eroded over time. Coastal processes including the direction of the alongshore sediment transport and the influence of engineering work associated with port construction can also be recognised. Within Lake Manzala, vegetated islands divide the lake into a series of sub-basins which can be clearly distinguished. The large influence of human activities within this lake can be identified and include reclamation for agriculture and the conversion of parts of the lake bed for fish farms. The historical images available for the three lagoons provide important insights into decadal scale changes, which have been greatest at Lake Manzala. Since the early 1970s large parts of the lake, in particular in the southwest where the shoreline has migrated northwards, have been reclaimed. Major engineering works, such as the El Salam Canal and road embankments, are shown to have resulted in significant lake change. The distribution of emergent vegetation within the lake has also changed. Classification of images for this lake into open water, vegetation and land enables the quantification of these changes. Between 1973 and 2003, the lake declined in area by approximately 50%. Changes at Merja Zerga over the last three decades include reconfiguration of the marine outlet and the expansion of the internal delta at the end of the Nador Canal. The images of this site clearly demonstrate the intensification of agriculture around the lagoon. The most marked changes evident within the images of Ghar El Melh concern the sand bars that separate the lagoon from the sea. Geomorphological processes operating within the coastal zone have resulted in the straightening of the bars with central sections migrating out towards the sea. Remote sensing is established as a promising application for detecting the quantitative surface cover changes in coastal lagoons and their near landscapes. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons     

基于土地利用变化的细河流域景观生态风险评估

以辽宁省细河流域为研究对象,利用1985、1995年和2005年3个时期的Landsat TM及2015年Landsat OLI遥感数据,进行了细河流域土地利用解译,定量分析了流域近30年来土地利用动态变化特征;根据景观生态学理论引入景观生态风险评价模型,将研究区划分为340个生态风险评价单元,基于地统计学和空间自相关方法,对1985—2015年细河流域景观生态风险时空分布特征及空间关联格局进行了评价。结果表明:(1)自1985年以来,研究区的6种土地利用类型皆发生了变化,其中建设用地由于林地和耕地的大量转入增加最明显。(2)1985—2015年流域高、较高和中生态风险区面积增加,且向流域南部转移;低、较低生态风险区面积减少,且向流域北部集聚;流域整体生态风险呈增高趋势。(3)研究区各时期景观生态风险呈现正的空间相关性,在空间上趋于集聚。人类活动干扰导致景观破碎,是影响该区域景观生态风险最重要的原因。     

Landscape pattern and eco-hydrological charactedstics at the upstream of Minjiang River,China

Based on three scenes of Landsat 5 Thematic Mapper (TM) satellite images acquired on June 26,1994,12 land cover types were identified by the supervised classification techniques.The precipitation,runoff,and normalized difference vegetation index (NDVI) data of six catchments were accumulated from April to September in 1992,1993,and 1995.A new eco-hydrological index,expressed by the difference between precipitation and runoff divided by the product of precipitation and NDVI,was used in this study to represent the eco-hydrological functions of different catchments.The results were:(1) The selected six catchments at the upstream of Minjiang River,China were different in landscape patterns in terms of landscape type and cover.There were higher contagion,lower edge density and diversity index in the Shouxi catchments and lower contagion,higher edge density and diversity index in the Zagunao catchments.(2)Eco-hydrological indexes had remarkable differences among different catchments.The highest eco-hydrological index was found in the Shouxi catchments,which indicated higher precipitation holding capacity of vegetation therein.While the lower eco-hydrological index was found in the Zagunao catchments,which indicated its lower precipitation holding capacity of vegetation.(3) High correlation was detected between the landscape indexes and eco-hydrological indexes.Eco-hydrological index was positively correlated with landscape contagion in contrast with the negative correlation with landscape diversity and edge density.     

Satellite image texture and a vegetation index predict avian biodiversity in the Chihuahuan Desert of New Mexico

Predicting broad-scale patterns of biodiversity is challenging, particularly in ecosystems where traditional methods of quantifying habitat structure fail to capture subtle but potentially important variation within habitat types. With the unprecedented rate at which global biodiversity is declining, there is a strong need for improvement in methods for discerning broad-scale differences in habitat quality. Here, we test the importance of habitat structure (i.e. fine-scale spatial variability in plant growth forms) and plant productivity (i.e. amount of green biomass) for predicting avian biodiversity. We used image texture (i.e. a surrogate for habitat structure) and vegetation indices (i.e., surrogates for plant productivity) derived from Landsat Thematic Mapper (TM) data for predicting bird species richness patterns in the northern Chihuahuan Desert of New Mexico. Bird species richness was summarized for forty-two 108 ha plots in the McGregor Range of Fort Bliss Military Reserve between 1996 and 1998. Six Landsat TM bands and the normalized difference vegetation index (NDVI) were used to calculate first-order and second-order image textures measures. The relationship between bird species richness versus image texture and productivity (mean NDVI) was assessed using Bayesian model averaging. The predictive ability of the models was evaluated using leave-one-out cross-validation. Texture of NDVI predicted bird species richness better than texture of individual Landsat TM bands and accounted for up to 82.3% of the variability in species richness. Combining habitat structure and productivity measures accounted for up to 87.4% of the variability in bird species richness. Our results highlight that texture measures from Landsat TM imagery were useful for predicting patterns of bird species richness in semi-arid ecosystems and that image texture is a promising tool when assessing broad-scale patterns of biodiversity using remotely sensed data.     

Landsat TM inventory and assessment of waterbird habitat in the southern <Emphasis Type="Italic">altiplano</Emphasis> of South America

The diverse set of wetlands in southern altiplano of South America supports a number of endemic and migratory waterbirds. These species include endangered endemic flamingos and shorebirds that nest in North America and winter in the altiplano. This research developed maps from nine Landsat Thematic Mapper (TM) images (254,300 km²) to provide an inventory of aquatic waterbird habitats. Image processing software was used to produce a map with a classification of wetlands according to the habitat requirements of different types of waterbirds. A hierarchical procedure was used to, first, isolate the bodies of water within the TM image; second, execute an unsupervised classification on the subsetted image to produce 300 signatures of cover types, which were further subdivided as necessary. Third, each of the classifications was examined in the light of field data and personal experience for relevance to the determination of the various habitat types. Finally, the signatures were applied to the entire image and other adjacent images to yield a map depicting the location of the various waterbird habitats in the southern altiplano. The data sets referenced with a global positioning system receiver were used to test the classification system. Multivariate analysis of the bird communities censused at each lake by individual habitats indicated a salinity gradient, and then the depth of the water separated the birds. Multivariate analysis of the chemical and physical data from the lakes showed that the variation in lakes were significantly associated with difference in depth, transparency, latitude, elevation, and pH. The presence of gravel bottoms was also one of the qualities distinguishing a group of lakes. This information will be directly useful to the Flamingo Census Project and serve as an element for risk assessment for future development.This revised version was published online in March 2005 with corrections to the issue cover date.     

Impact of LUCC on landscape pattern in the Yangtze River Basin during 2001–2019

Evaluating the influences of LUCC (Land Use/Land Cover Change) on landscape pattern is significant for understanding and improving ecological environment system management. This study used landscape pattern as an important indicator to estimate the impacts of the LUCC in the Yangtze River Basin from 2001 to 2019. Based on the remote sensing images of LULC (Land Use/Land Cover) in the Yangtze River Basin in 2001–2019, the dynamic attitude and transfer matrix of LULC, and landscape pattern indices were employed to analyze the LUCC and the impact of LULC on the landscape pattern of the Yangtze River Basin. The results of LUCC show that the main LUCC in the Yangtze River Basin during 2001–2019 is mainly manifested by the increase of water body, forest, wetland, crop/natural vegetation mosaic (NVM) and urban, among which the forest increased the most by 62,635 km². The areas of grassland and cropland are decreasing, with the grassland decreasing the most. Forest, crop/NVM and cropland are transformed into grassland, which complements the lack of grassland to some extent. LUCC in the Yangtze River Basin is most intense between grassland and forest. Landscape pattern shows: Grassland occupies an important advantage in the whole landscape structure. Forest, grassland and urban landscapes are seriously fragmented, and their LSI (Landscape Shape Index) is more complex than others. The connectivity between various landscape types is weakened, and the degree of landscape fragmentation is increased, but the LULC structure is becoming more and more abundant. The areas with high landscape fragmentation value have richer landscape diversity and diverse LULC types. There is a strong correlation between grassland and the four landscape pattern indices. The change of landscape pattern in the Yangtze River Basin is influenced by natural factors and LUCC in the Yangtze River Basin, and the change caused by human activities is the main driving factor of LUCC.     

南京市城乡梯度上景观变化的空间与数量稳定性

为揭示城市化过程中景观稳定性及其区位分异,本文在多时相Landsat TM遥感影像的支持下,应用Kappa指数方法对1988—2008年间南京市城乡梯度上景观要素(除丘陵山地及大规模水体外)的空间位置变化与数量变化进行了研究。结果表明:耕地的数量稳定性较高,但空间位置稳定性较低;而聚落用地空间位置稳定性较高,但数量稳定性却较低;水体的空间位置和数量稳定性都比较高;林地和其他用地的数量以及空间位置稳定性都比较低。在城乡梯度上,随着城市化程度增加,景观的空间位置稳定性呈上升趋势,而数量稳定性则表现出下降趋势。对于已完成城市化的中心城区,景观的数量稳定性迅速上升,其景观要素的组成和空间分布特征均趋于稳定。聚落用地和耕地的空间位置和数量稳定性在不同城乡梯度带间变化较大,而水体和林地的空间与数量稳定性受城市化过程影响较小。     

南京市城区景观特征尺度动态

利用南京市1988、1998和2006年Landsat TM遥感影像,采用小波分析技术,对1988—2006年南京市中心城区的景观结构特征进行了研究.结果表明：应用小波分析技术分析景观样带数据时,取样宽度过小易导致检测结果的不稳定,而样带过宽则易导致较小尺度特征的丢失,应采用合适的样带宽度;基于TM影像（30 m空间分辨率）的南京市城区样带宽度以4个像元为最佳.1988、1998和2006年,南京市中心城区都存在4个相对稳定的特征尺度域,分别对应于功能小区、小型街区、中型街区和大型街区;研究期间,大型街区的特征尺度几乎没有变化,而其它3个尺度域的变化相对较大,但各尺度域的变化趋势一致;各尺度域内特征尺度之间的差异性均逐渐变小,表明期间中心城区的结构特征越来越稳定,不同部位的空间结构趋同,且各尺度域的变化有较强的同步性.     

1990—2015年三江平原生态功能区水禽栖息地适宜性动态

作为国际重要湿地,三江平原生态功能区是重要的水禽栖息地.随着人类活动干扰、土地利用和全球气候变化,栖息地适宜性逐渐引起生态学家的重视.本文以Landsat TM/ETM+/OLI和HJ-1B为遥感信息源,采用面向对象分类方法提取土地覆被空间信息;采用综合熵值法和层次分析法确定水源状况(湖泊和河流密度)、干扰条件(居民地和道路密度)、遮蔽物(土地覆被类型和坡度)和食物丰富度(NDVI)等因子的权重;根据水禽栖息地适宜性评价系统获得三江平原生态功能区1990、2000、2010和2015年水禽栖息地适宜性结果,并分析其时空分布和变化特征及驱动因素.结果表明: 近25年间,三江平原生态功能区水禽栖息地适宜性最好区域面积减少3.2%,主要由于湿地开垦和退化;适宜性最好区域空间分布特征明显,主要分布于黑龙江、挠力河、乌苏里江、穆棱河以及兴凯湖等水补给充足的沿岸区域.适宜性良好的区域主要分布在饶河县,到2010和2015年,虎林县和抚远县也变为适宜性良好区域的重要分布区,主要由于该区水田面积大幅增加.适宜性一般区域分布较零散,其面积先增加后减少.适宜性差的区域面积在1990—2000年间增加6.7%,2000—2015年间减少3.1%.土地覆被变化是水禽栖息地适宜性等级变化的最重要影响因素;人口和经济增长以及气候的变干、变暖使水禽栖息地适宜性降低;保护区的建立使水禽栖息地得到有效保护.     

1995—1999年黄河三角洲东部自然保护区湿地景观格局变化

基于1995和1999年的Landsat TM遥感影像,结合地理信息系统技术,分析黄河改道清8汊（1996年）前后的1995—1999年黄河三角洲东部自然保护区（位于黄河现行流路入海口处）湿地景观格局的变化特征,以及影响湿地景观格局变化的驱动因素.结果表明：1995—1999年,保护区湿地仍以天然湿地为主,人工湿地比重极小,期间非湿地面积大幅增加,而天然湿地和人工湿地面积则呈下降趋势,其中,裸露淤泥质滩涂和沼泽湿地面积明显萎缩;尽管保护区湿地景观类型、形状、结构的变化程度不均一,且各景观类型在空间分布上的团聚程度变化不均衡,但总的看来,保护区景观整体结构趋于复杂化,破碎化程度有所加深,内部各景观类型从大块连续的镶嵌分布向小块离散分布转变;影响保护区湿地景观格局变化的主要因素有3个：黄河改道、黄河断流和人类活动.     

旅游干扰下流域多尺度景观格局演化特征及驱动因素——以新安江流域为例

流域景观是旅游活动的核心吸引物之一,亦是探究旅游干扰对大尺度生态环境影响极具操作性的研究对象。基于Landsat系列遥感影像,以新安江流域为案例地,按照"流域-旅游热点区-景区"逐级递进的研究尺度,深入剖析旅游干扰背景下的流域景观格局演化过程,并借助格网和地理探测器等方法测度旅游干扰背景下的流域景观格局驱动因素,结果表明：（1）新安江流域以林地景观为主,整体景观格局受人为干扰程度逐年加剧,景观异质性提升,景观结构趋于均衡发展;（2）新安江流域高强度的旅游活动未加剧旅游热点区内的景观格局恶化趋势,但致使景区景观破碎化加剧,林地等优势景观的优势度和完整性降低,景观多样性提升;（3）新安江流域景观格局主要受河湖、城市、景区等干扰源影响,地形地貌是景观格局演化的核心驱动维度,而气候、工业发展水平和交通等维度对流域景观格局整体影响力较小;（4）旅游维度中的距高级别景区距离因子对景观格局作用显著,但接待旅游人数和旅游直接收入对景观格局解释力较低,旅游对流域景观格局的干扰具有尺度局限效应。     

岷江上游林农边界网络的生态效应

应用地理信息系统软件从遥感影像中提取出岷江上游的农田边界类型图,结合坡面尺度上林农边界效应的分析结果,对林农边界效应在景观尺度上的影响进行了研究。结果表明:研究区的农田边界共有5种类型,分别是农田与林地、灌木林地、草地、水体、建筑用地之间的边界,其中林农边界长2473.68km,占农田边界的37.57%,广泛分布在岷江干流及其支流的河谷中,在很大范围上影响着农田的土壤水分和生物多样性,对林地的影响相对较小;边界效应使林地边缘和农田边缘的土壤水分低于其内部,研究区有2103hm2的农田和371hm2的林地的土壤水分受到边界网络影响,分别占研究区农田面积和林地面积的2.33%和0.03%。由于土壤水分是制约研究区植物生长的限制性因子,且岷江上游的农田斑块面积较小且分布零散,因此应避免农林复合景观中边界密度进一步增加。     

基于NDVI假彩色合成法的土地覆被变化监测

土地覆被变化监测对区域生态系统保护、环境变化研究具有重要的作用,研究旨在提供一种基于归一化植被指数(NDVI)的假彩色合成法的土地覆被变化监测方法。该研究以黄河三角洲为研究区,以3期 Landsat TM影像(成像时间分别为1987年5月7日,1998年5月5日,2009年5月3日)为数据源,在进行相对辐射校正的基础上,生成3期NDVI图像,然后分别以三期的NDVI图像作为红、绿和蓝波段生成假彩色合成图像。基于彩色合成原理,对黄河三角洲的1987-2009年间的土地覆被变化进行了分析。结果表明:(1) 假彩色合成图像上的灰白色区域表示其土地覆被状态稳定,三个时期的NDVI值均较大,黑色区域的土地覆被状态也较稳定,但是三个时期的NDVI值均较小,而青色、绿色、红色则反映相应地区的NDVI处在不稳定状态;(2)不同的颜色反映了不同的土地覆被变化方式,较为直观地反映了土地覆被的变化特点,尤其是自然植被与农田之间的转换;(3)限于NDVI的瞬时性,该方法需要与基于遥感影像分类的方法相结合,才能更好地监测土地覆被变化。     

Identifying Dicymbe corymbosa Monodominant Forests in Guyana Using Satellite Imagery

The ectomycorrhizal (EM) canopy tree Dicymbe corymbosa (Fabaceae subfam. Caesalpinioideae) forms monodominant forests in the Pakaraima Mountains of western Guyana. Like other tropical monodominants, D. corymbosa has several life-history traits that promote conspecific clumping, in contrast to density-dependent recruitment limitations characterizing most tropical trees. Dicymbe corymbosa forests, occurring in Guyana as patches within a largely non-EM mixed-species forest matrix, are important habitats for a diverse assemblage of EM fungi. Ground-based studies have not adequately determined the regional extent of D. corymbosa forests, nor are they practical due to the rugged, remote nature of the Pakaraima Mountains. We assessed the suitability of Landsat satellite imagery for mapping regional distribution of D. corymbosa forests in Guyana's Upper Potaro River Basin. Supervised image classification was performed on images from August 1989 (Landsat-5 TM) and October 1999 (Landsat-7 ETM+). In situ forest reference data were used to quantitatively assess accuracy of output classification maps. Classification performed well in distinguishing monodominant from mixed-species forests. For both images, D. corymbosa forest class accuracy was good (1989 user's accuracy = 89.8%, K_hat = 0.74; 1999 user's accuracy = 80.7%, K_hat = 0.59). The resulting output classification maps will be useful for planning fungal surveys and ecological studies in forests of the Pakaraima region. Classification of Landsat images may be effective for identifying monodominant forests in other remote regions of the tropics.     

Tracking palustrine water seasonal and annual variability in agricultural wetland landscapes using Landsat from 1997 to 2005

Wetlands densely populate the ecoregion transecting the center of the Prairie Pothole Region (PPR) known as the Missouri Coteau and epicenter to the most productive waterfowl‐breeding habitat in North America. These palustrine, depressional basin waters vacillate with regional drought and deluge, so surface water fluctuations over time modulate wetland productivity, habitat, and water quality functions. Models predict formidable effects of climate change on glacial basin surface waters, yet large‐scale, long‐term observation data are lacking to compare against predicted changes. Current, optical‐based water detection models do not delineate marsh vegetation from shallow, turbid, high‐chlorophyll waters common to the region. We developed a palustrine wetland spectral model for tracking open surface waters using Landsat imagery, which we evaluated for a 2500 km² landscape that estimates seasonal and annual open water variability for thousands of individual wetlands in the Missouri Coteau ecoregion. Detection accuracy of 96% was achieved for water bodies greater than a half‐pixel in size. We identified shifts in the distribution of water permanence classes within and between years for waters emerging in spring, mid‐summer, and late summer from 1997 to 2005 and identified a maximum of 19 047 basins with open water (12% of the landscape) populating 2500 km². For the 2005 growing season, we observed only 8757 basins with open water (6% of the landscape) for the same area. Declines were greatest for water bodies detected only in spring, suggesting a loss of those wetlands functioning to recharge groundwater stores early in the season and a high sensitivity to observed reductions in snowfall. If landscape factors driving open water coverage and wetland density are similar for the entire Missouri Coteau, we estimate the number of basins containing at least a pixel of water for this region declined from 577 600 to 266 000 between 1997 and 2005.     

基于InVEST模型的海南岛三大流域生境质量时空演变

基于1980—2020年5期土地利用数据,采用InVEST模型,综合应用土地利用转移、生境质量变化率和空间统计分析等方法,探究海南岛三大流域(南渡江、昌化江、万泉河)生境质量变化及其空间分布特征。结果表明: 海南岛三大流域土地利用类型以林地为主,占总面积的70%以上。1980—2020年间,海南岛三大流域建设用地面积增加量最大,达169.09 km²,主要来自耕地和林地。研究区生境质量整体呈现出上游源头区高、中下游区域低的空间分布格局,研究期间生境质量指数总体表现为先略微升高后显著降低的变化特征。在三大流域中,万泉河流域生境质量最高,昌化江流域次之,南渡江流域最低,且南渡江流域生境质量波动较大,受人为干扰较强。1980—2020年间,三大流域生境质量变化率总体降低0.5%,且在2010—2020年间退化明显。1980—2020年间,研究区生境质量在空间分布上具有较强的自相关性和显著的聚集性。三大流域生境质量的热点区主要集中在流域上游源头区域;冷点区主要分布在三大流域的入海口区域以及南渡江的中下游地区。研究结果可为海南岛三大流域生物多样性保护和生态修复提供数据支撑及科学参考。     

Differentiating geological fertility derived vegetation zones in Kruger National Park,South Africa,using Landsat and MODIS imagery

Spatial technologies present possibilities for producing frequently updated and accurate habitat maps, which are important in biodiversity conservation. Assemblages of vegetation are equivalent to habitats. This study examined the use of satellite imagery in vegetation differentiation in South Africa's Kruger National Park (KNP). A vegetation classification scheme based on dominant tree species but also related to the park's geology was tested, the geology generally consisting of high and low fertility lithology. Currently available multispectral satellite imagery is broadly either of high spatial but low temporal resolution or low spatial but high temporal resolution. Landsat TM/ETM+ and MODIS images were used to represent these broad categories. Rain season dates were selected as the period when discrimination between key habitats in KNP is most likely to be successful. Principal Component Analysis enhanced vegetated areas on the Landsat images, while NDVI vegetation enhancement was employed on the MODIS image. The images were classified into six field sampling derived classes depicting a vegetation density and phenology gradient, with high (about 89%) indicative classification accuracy. The results indicate that, using image processing procedures that enhance vegetation density, image classification can be used to map the park's vegetation at the high versus low geological fertility zone level, to accuracies above 80% on high spatial resolution imagery and slightly lower accuracy on lower spatial resolution imagery. Rainfall just prior to the image date influences herbaceous vegetation and, therefore, success at image scene vegetation mapping, while cloud cover limits image availability. Small scale habitat differentiation using multispectral satellite imagery for large protected savanna areas appears feasible, indicating the potential for use of remote sensing in savanna habitat monitoring. However, factors affecting successful habitat mapping need to be considered. Therefore, adoption of remote sensing in vegetation mapping and monitoring for large protected savanna areas merits consideration by conservation agencies.