Assessing landscape structure and pattern fragmentation in semiarid ecosystems using patch-size distributions

Spatial vegetation patterns are recognized as sources of valuable information that can be used to infer the state and functionality of semiarid ecosystems, particularly in the context of both climate and land use change. Recent studies have suggested that the patch-size distribution of vegetation in drylands can be described using power-law metrics, and that these scale-free distributions deviate from power-law linearity with characteristic scale lengths under the effects of increasing aridity or human disturbance, providing an early sign of desertification. These findings have been questioned by several modeling approaches, which have identified the presence of characteristic scale lengths on the patch-size distribution of semiarid periodic landscapes. We analyze the relationship between fragmentation of vegetation patterns and their patch-size distributions in semiarid landscapes showing different degree of periodicity (i.e., banding). Our assessment is based on the study of vegetation patterns derived from remote sensing in a series of semiarid Australian Mulga shrublands subjected to different disturbance levels. We use the patch-size probability density and cumulative probability distribution functions from both nondirectional and downslope analyses of the vegetation patterns. Our results indicate that the shape of the patch-size distribution of vegetation changes with the methodology of analysis applied and specific landscape traits, breaking the universal applicability of the power-law metrics. Characteristic scale lengths are detected in (quasi) periodic banded ecosystems when the methodology of analysis accounts for critical landscape anisotropies, using downslope transects in the direction of flow paths. In addition, a common signal of fragmentation is observed: the largest vegetation patches become increasingly less abundant under the effects of disturbance. This effect also explains deviations from power-law behavior in disturbed vegetation which originally showed scale-free patterns. Overall, our results emphasize the complexity of structure assessment in dryland ecosystems, while recognizing the usefulness of the patch-size distribution of vegetation for monitoring semiarid ecosystems, especially through the cumulative probability distributions, which showed high sensitivity to fragmentation of the vegetation patterns. We suggest that preserving large vegetation patches is a critical task for the maintenance of the ecosystem structure and functionality.     

Application of Markov-chain model for vegetation restoration assessment at landslide areas caused by a catastrophic earthquake in Central Taiwan

The 921 earthquake caused a catastrophic disaster in Central Taiwan. Ten years have passed since the earthquake occurred. Vegetation succession is the basis for establishing a restoration reference which plays an important role in vegetation restoration at landslide sites. Generally, growth conditions for grass are easier and the growth rate is faster than that for trees. Therefore, grass can be considered a pioneer species or an important reference for the early vegetation succession stage. This is the reason why grass is required to be extracted from other land covers. Integrating remote sensing, geographic information system and image classification into vegetation succession models is very important. In this study, the Markov chain model was applied for vegetation restoration assessment and discussion. Chiufenershan and Ninety-nine peaks were selected as the study areas. Five SPOT satellite images are used for land cover mapping and vegetation restoration simulations. Four categories of land covers were extracted, including forest, grass, bare land and water, respectively. From the transitive probability matrix (derived from any two land covers), the results show that vegetation restoration at the Chiufenershan and Ninety-nine peaks landslide areas is ongoing, but that has been disturbed by natural disasters.     

1994—2008年河南省植被净第一性生产力及其时空变化

基于地理信息系统和卫星遥感技术,利用地面气象数据、遥感数据和土地分类等数据,根据河南省实际植被覆盖和自然地理情况,应用改进的CASA模型估算了1994—2008年间河南省植被净第一性生产力及其时空变化。结果表明：河南省植被净第一性生产力与年均温度的相关性好于植被年净第一性生产力与年降水量和年均太阳辐射之间的相关性,温度是限制河南省植被净第一性生产力的主要因子;15年来河南省植被净第一性生产力呈增加趋势,但不明显;河南省主要植被类型的净第一性生产力从大到小依次为林地、灌丛、耕地、草地、其它植被,它们随时间的变化趋势极为一致。     

红河哈尼梯田世界文化景观遗产的遥感监测与土地覆盖变化

红河哈尼梯田是中国重要的世界文化景观遗产,以森林、梯田、村寨、水系四度同构的人与自然高度协调的生态系统而著称。随着经济与旅游的发展,哈尼梯田自申报世界遗产以来,其文化景观不可避免地遭受干扰。遗产监测有助于及时了解遗产本体的保存现状和风险影响因素,确定遗产突出普遍价值以及制定规避风险的有效措施。文章基于红河哈尼梯田独特的文化景观特征,利用高分辨率卫星遥感影像对申遗前后的文化景观遗产要素进行遥感监测,分析其土地覆盖现状与变化趋势,探究遥感手段在遗产要素变化监测中的可行性与可靠性,对遥感在文化遗产监测中的应用具有一定的指导意义。结果表明,(1)红河哈尼梯田申遗后,景观格局基本没有发生改变,仍然以森林和梯田为主,其遗产要素的变化均在可控范围内。主要申遗范围坝达片区各遗产要素面积变化共为93.78 hm²,水田变化约占总变化面积的80%,其次是林地约占18%,其他遗产要素面积变化不大。(2)各遗产要素之间的面积变化以水田转变为林地和灌木林地为主,占总变化面积的57%,部分房屋建筑物拆迁变为灌木林地,说明申遗后相关的退耕还林政策与生态环境保护规划起到了明显成效。(3)随着旅游业的发展,以及村民生活条件改善的需求,部分梯田转变为道路和房屋建筑,但这些规划的合理性还需进一步核实与确认。(4)依据哈尼梯田的文化景观特征,监测文化景观遗产要素时的精细化程度比土地利用变化要求高,因此首选高分辨率遥感影像,建议空间分辨率达到1 m以上。     

半干旱黄土区退耕还林十年植被恢复变化分析——以陕西吴起县为例

黄土高原退耕还林（草）政策实施已逾10 a,了解植被恢复变化状况及存在的问题,对于制定和完善生态环境治理方略具有重要意义。以吴起县为例,基于实地调查及遥感等数据,对退耕还林（草）以来植被覆盖度、主要植被类型变化及不同立地条件下植被恢复变化的差异进行了定量分析。结果表明：2000年至2009年,植被覆盖度大于30%的面积在全县总面积中的比例由不足1%上升至91.96%;其中缓坡立地类型上的乔灌林地类型面积增长最为显著,而阳向陡坡等恶劣生境下的植被恢复缓慢;有林地、灌木林地及疏林地均呈现规模增大趋势,属扩张状态;中覆盖度草地、低覆盖度草地、坡耕地及耕地呈现规模减少趋势,属缩减状态。     

欧盟土壤环境评价监测项目及其对我国农用地质量监测的启示

＂十二五＂期间,我国国土资源调查评价的重点任务之一是建立农用地质量监测体系。当前我国农用地质量变化监测技术仍然处于研究探索阶段,欧盟土壤环境评价监测项目是较为成熟的监测项目,可为中国农用地质量监测工作提供借鉴。文章分别就欧盟土壤环境评价监测的相关研究和国内学者对农用地质量监测的研究进行了综述,认为欧盟土壤环境评价监测项目在指标选取、监测网络建立、数据更新技术等方面建立了较为成功的机制。未来中国农用地质量监测工作可在关注土壤环境质量、分类土壤退化原因、针对性地选取指标、应用DPSIR模型、确定监测点的方法、充分利用原有监测网络和监测数据等方面借鉴欧盟经验。     

Satellite detection of bird communities in tropical countryside.

The future of biodiversity hinges partly on realizing the potentially high conservation value of human-dominated countryside. The characteristics of the countryside that promote biodiversity preservation remain poorly understood, however, particularly at the fine scales at which individual farmers tend to make land use decisions. To address this problem, we explored the use of a rapid remote sensing method for estimating bird community composition in tropical countryside, using a two-step process. First, we asked how fine-grained variation in land cover affected community composition. Second, we determined whether the observed changes in community composition correlated with three easily accessible remote sensing metrics (wetness, greenness, and brightness), derived from performing a tasseled-cap transformation on a Landsat Enhanced Thematic Mapper Plus image. As a comparison, we also examined whether the most commonly used remote sensing indicator in ecology, the Normalized Difference Vegetation Index (NDVI), correlated with community composition. We worked within an agricultural landscape in southern Costa Rica, where the land comprised a complex and highly heterogeneous mosaic of remnant native vegetation, pasture, coffee cultivation, and other crops. In this region, we selected 12 study sites (each < 60 ha) that encompassed the range of available land cover possibilities in the countryside. Within each site, we surveyed bird communities within all major land cover types, and we conducted detailed field mapping of land cover. We found that the number of forest-affiliated species increased with forest cover and decreased with residential area across sites. Conversely, the number of agriculture-affiliated species using forest increased with land area devoted to agricultural and residential uses. Interestingly, we found that the wetness and brightness metrics predicted the number of forest- and agriculture-affiliated species within a site as well as did detailed field-generated maps of land cover. In contrast, NDVI and the closely correlated greenness metric did not correlate with land cover or with bird communities. Our study shows the strong potential of the tasseled-cap transformation as a tool for assessing the conservation value of countryside for biodiversity.     

南疆西部不同植被类型NDVI对风沙灾害的响应

不同植被类型对风沙灾害的响应研究有助于风沙灾害的遥感监测评估和防灾减灾工作。采用传统统计学和空间自相关方法,利用MODIS的每日反射率和土地类型产品,分析了风沙灾害后南疆西部不同植被类型NDVI的变化规律及其空间分布特征。结果表明：风沙灾害后,研究区不同植被类型NDVI的差异在增大,NDVI变化值在一0．3865~0．4148之间,NDVI减小的面积占整个研究区面积的54．98％,变异系数增大值在2．44％～36．75％之间;受到风沙灾害的影响,研究区植被NDVI全局Moran’SI系数从0．7982减小到0．6786,但在空间上仍存在显著的正相关性,具有显著的空间集聚特征;由NDVI差值的局部空间自相关指标集聚图以及不同植被类型NDVI差值的空间关联区域面积百分比,可以发现落叶针叶林和裸地或低植被覆盖地受风沙灾害的影响较小,郁闭灌丛和作物受风沙灾害的影响较大。上述关于风沙灾害后南疆西部不同植被类型的变化及其空间格局的研究结果,不仅证明了防护林的风沙阻挡作用,也可以为风沙灾害的防治工作提供参考依据。     

区域水土流失遥感与核素示踪联合评价技术研究

水土流失遥感调查具有宏观、快速、效率高的优点,可以实现水土流失时空动态监测;侵蚀137Cs核素示踪技术能够提供独立的土壤侵蚀与堆积数据以及空间分布的信息,与其它方法相比,不仅具有无时空限制、操作简便快捷的优点,而且可提供上世纪60年代以来的多空间尺度(测点到流域)年均净侵蚀量。核素示踪与遥感解译的结合,可实现水土流失评价的宏观与微观、点与面、估算与实测的结合,大大地提高水土流失评价时空分辨率和精准度。文章以锦屏二级水电站工程建设区域为例,将137Cs侵蚀示踪技术和水土流失遥感调查方法相结合,基于GIS技术,对区域内水土流失现状进行了评价。     

Chalk and limestone quarries as wildlife habitats

Natural recolonisation by volunteer species of chalk and limestone quarries has led to the development of attractive and species-rich communities in many parts of the United Kingdom. These communities have a basic similarity in floristic composition wherever they occur, but they also show a great deal of individual variation resulting from differences in the location, history and variability of the quarry itself and in the nature of the surrounding habitats. The interest of old quarries may be enhanced by the presence of individually rare or local species and especially by their refuge status in relation to the loss of semi-natural calcareous grassland in the district. It is suggested that some sites play an important role in wildlife conservation and that this factor should be considered in any programme of land reclamation. Natural regeneration is very slow compared with the rate of land use in modern quarrying but the development of ecological techniques may make it possible to rehabilitate derelict and barren sites for amenity and conservation purposes using older quarries as models.     

The development and application of remote sensing to monitor sand dune habitats

Sand dunes are complex systems that contain several habitats, often as mosaics or transitions between types. Several of these habitats are afforded protection under European Legislation and in the UK nationally within Special Areas of Conservation (SAC) and Sites of Special Scientific Interest (SSSI). Natural England has a statutory duty to report to Europe on the conservation status and condition of sand dunes; and is required to report to the UK Government on designated sites. To achieve this we have sought ways of capturing, analysing and interpreting data on the extent and location of sand dune habitats. This requires an ability to be able to obtain data over large areas of coastline in an efficient way. Natural England and Environment Agency Geomatics have worked collaboratively for over 16 years, sharing data and ecological knowledge. In 2012 work started to evaluate the use of remote sensing to map UK BAP and Annex I sand dune habitats. A methodology has now been developed and tested to map sand dune habitats. The key objective was to provide an operational tool that will help to map these habitats and understand change on sites around England. This has been achieved through analysis of LIDAR and Compact Airborne Spectrographic Imager (CASI) data using Object Orientated Image Analysis. Quality Control (QC) and accuracy assessments have shown this approach to be successful and 11 sites have been mapped to date. These techniques are providing a new approach to monitoring change in coastal vegetation communities and informing management of protected sites.     

基于MODIS数据的河南省冬小麦产量遥感估算模型

小麦是世界上最重要的粮食作物,小麦生产对中国的粮食保障起着十分重要的作用,及时、准确、大范围对小麦产量进行监测预报,对于农学经济发展和粮食政策制定具有极为重要的现实意义。对作物产量进行遥感监测的原理是建立在其遥感特征基础之上的,通过建立作物长势指标与遥感信息的定量关系,可实现对作物产量的监测预报。文章基于2009年MODIS遥感数据和气象数据,利用Arcgis和ENVI提取纯小麦像元,并提取纯小麦像元对应的NDVI、NPP和LAI,获取分县NDVI、NPP和LAI均值,利用统计软件对产量数据和分县遥感参数均值进行数据整理和分析,建立了河南省冬小麦产量估算模型。以往研究多采用遥感图像上某像元和地面调查点进行研究,具有很大的不确定性,文章以县为单位,对冬小麦平均单产和县域内冬小麦种植像元遥感参数的均值进行相关研究,提高了模型模拟精度。同时文章选用多种遥感参数和多项气象因子建立估产模型,避免了针对一个参数进行估产的局限性。在最佳时相的选择上,根据冯美辰（2010）以往的研究结果,从4月以后,5月8日和4月20Et植被指数和产量相关性最大,4月份之前冬小麦处于返青到拔节期,对产量来说还有很多不确定闪素,因此文章选用5月8El和4月20日进行冬小麦估产研究。结果表明,5月8日的估产模型优于4月20日,加入气象冈子的遥感气象估产模型优于只采用遥感参数进行估产的遥感模型。利用2010年产量数据对模型精度进行检验,遥感气象模型预测精度在70．2％N99．7％之间,平均精度为90．7％;遥感模型预测精度在68．1％到95．5％之间,平均精度为83．9％。表明遥感气象模型模拟精度更高,其精度可以满足大面积估产要求,可以对产量预报提供科学参考。     

2000—2007年珠峰自然保护区植被时空变化与驱动因子

采用遥感与GIS相结合的方法研究了珠峰自然保护区2000—2007年之间的植被时空变化过程和驱动机制问题。通过一元线性回归斜率计算获取了基于EVI数据的珠峰自然保护区植被变化趋势,以及表现2000—2007年植被变化的矢量图层。利用GIS时间动画技术,建立了7个时间点内不同间隔的植被时空演化过程快照,并结合ArcEngine构建了植被变化监测的时序分析流程,提取和分析了植被变化过程的时空特征。依据年平均温和年降水量观测记录进行了植被变化的气候因子分析,依据道路、河流缓冲区的居民点密度与植被退化面积比例的相关性,分析了人类活动影响,并讨论了不同植被退化区域在多重因素作用下的变化驱动因子。拟合了主要社会经济发展指标与植被变化的相关性,从统计数据方面讨论了珠峰自然保护区社会经济发展对植被变化的影响作用。结果表明：珠峰自然保护区植被变化的总体趋势以稳定为主,但植被退化趋势超过了变好趋势。同时,核心区植被变好趋势明显,实验区植被退化趋势严重。保护区南坡植被受气候变化干扰小,保持了大部分变好趋势;北坡由于降水减少造成湿地植被退化,对草地的长势带来消极作用。人类活动与植被状态变化有密切关系,在沟谷地带的破坏作用明显。并且,植被退化趋势与农业耕地面积扩大以及放牧影响关联紧密,而牲畜饲养与林业发展都未对保护区植被变化造成明显影响。     

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.     

Using soundscapes to detect variable degrees of human influence on tropical forests in Papua New Guinea

There is global concern about tropical forest degradation, in part, because of the associated loss of biodiversity. Communities and indigenous people play a fundamental role in tropical forest management and are often efficient at preventing forest degradation. However, monitoring changes in biodiversity due to degradation, especially at a scale appropriate to local tropical forest management, is plagued by difficulties, including the need for expert training, inconsistencies across observers, and lack of baseline or reference data. We used a new biodiversity remote‐sensing technology, the recording of soundscapes, to test whether the acoustic saturation of a tropical forest in Papua New Guinea decreases as land‐use intensity by the communities that manage the forest increases. We sampled soundscapes continuously for 24 hours at 34 sites in different land‐use zones of 3 communities. Land‐use zones where forest cover was fully retained had significantly higher soundscape saturation during peak acoustic activity times (i.e., dawn and dusk chorus) compared with land‐use types with fragmented forest cover. We conclude that, in Papua New Guinea, the relatively simple measure of soundscape saturation may provide a cheap, objective, reproducible, and effective tool for monitoring tropical forest deviation from an intact state, particularly if it is used to detect the presence of intact dawn and dusk choruses.     

临策铁路沿线土地沙漠化敏感性评价

以临河至策克铁路为研究对象,选择土壤、地貌、植被类型作为沙漠化敏感性评价因子,根据TM遥感影像,参考铁路沿线有关资料,并结合现场调查,编制了铁路沿线地貌、土壤和植被图.采用图层权重 - 级别打分叠加模型,对铁路沿线土地沙漠化敏感性进行评价.结果表明,临策铁路大部分位于沙漠化高度敏感区,占全线长度的54.5%;极度敏感区占4.4%.这些区域也是风沙流主要分布地区,在铁路工程施工期及运营期应该采取有效保护措施,防止沙漠化土地的扩大与蔓延以及风沙流的加剧.     

Spatial error propagation when computing linear combinations of spectral bands: The case of vegetation indices

The collection of accurate and timely information on land use, crops, forest and vegetation are increasingly based on remote sensing spectral measurements produced by satellites. The most recent spacecrafts like the Earth Observing 1 (EO-1) produce a rich source of information being endowed with hyperspectral sensors that can provide up to 200 or more channels. In many instances such a multivariate signal has to be reduced to just one single value per pixel representing a particular characteristic of land. Linear combinations of bands are the general form of many indices. Since each individual image used to construct indices contains errors, when combined they produce a propagation of errors, a process that can distort a final output map. In this paper we measure the extent of error propagation when building linear vegetation indices. We consider three types of indices: the difference vegetation index (DVI), selected Kauth-Thomas indices (SBI, GVI and WET), and principal components, using benchmarking examples taken from the remote sensing literature. The main implication emerging from these examples is that the SBI and the first principal component are the indices more prone to error propagation. The formalization presented here allows a user to derive measures of error propagation in cases where technical characteristics of a sensor and physical characteristics of a landscape are known. These results can help a user to choose between alternative vegetation indices, and to associate a measure of reliability with such indices.     

Deriving state-and-transition models from an image series of grassland pattern dynamics

We present how state-and-transition models (STMs) may be derived from image data, providing a graphical means of understanding how ecological dynamics are driven by complex interactions among ecosystem events. A temporal sequence of imagery of fine scale vegetation patterning was acquired from close range photogrammetry (CRP) of 1 m quadrats, in a long term monitoring project of Themeda triandra (Forsskal) grasslands in north western Australia. A principal components scaling of image metrics calculated on the imagery defined the state space of the STM, and thereby characterised the different patterns found in the imagery. Using the state space, we were able to relate key events (i.e. fire and rainfall) to both the image data and aboveground biomass, and identified distinct ecological ‘phases’ and ‘transitions’ of the system. The methodology objectively constructs a STM from imagery and, in principle, may be applied to any temporal sequence of imagery captured in any event-driven system. Our approach, by integrating image data, addresses the labour constraint limiting the extensive use of STMs in managing vegetation change in arid and semiarid rangelands.     

Ecological modelling of nitrate pollution in small river basins by spreadsheets and GIS

With the increasing importance and awareness of water quality in the small basins, the modelling system is developed for monitoring and predictions of surface water pollution. The compartment model deals with basin characteristics extended by land cover attributes. The parameters of the model are estimated by experimental data of water quality together with land cover types that serve as nutrient detention media or transformers. The study examines methodology to determine the potential areas of nitrate pollution from point and non-point sources by remote sensing techniques. Classification of water, agricultural, forest and urban areas is processed with satellite images (LANDSAT 7). Whereas the agricultural and urban areas act as sources of pollution, forest zones operate as sinks. The nitrate levels are decreased downstream, if the proportion of the forest inside contribution zones increases. The modelling system is used to simulate amounts of nitrates in each compartment of the stream during the monitored period of one year. The number of compartments and their lengths are estimated on the basis of morphology of the basin. Simulation of the dynamic model is carried out with the TabSim. Geographic information system (GIS) and remote sensing tools are used to manage and estimate nitrate inflows from point and non-point sources of pollution. The article presents the spatial and time variation of the nitrate (NO₃⁻) within the basin of the stream Rakovnický (the west part of Bohemia, the whole area of 368 km²). It is shown that the model approach extended by the GIS and remote sensing can support decision-making process for better management practices in the basins.     

Evaluating the environmental flows of China's Wolonghu wetland and land use changes using a hydrological model, a water balance model, and remote sensing

Environmental flows are critical to sustaining a variety of plant and animal communities in wetlands. However, evaluation of environmental flows is hampered by the problem of hydrological and ecological data shortage, especially in many developing countries such as China. Based on a hydrological model, a water balance model and remote sensing data, we assessed the environmental flows of China's Wolonghu wetland with limited data. The hydrological model provides input data for the water balance model of the wetland, and the remote sensing data can be used to assess land use changes. Integration of these two models with the remote sensing data revealed both the environmental flows of the Wolonghu wetland and the relationships between these environmental flows and land use changes. The results demonstrate that environmental flows have direct and indirect influences on the wetland ecosystem and should be linked to sustainable wetland management.