54 results on '"Skidmore AK"'
Search Results
2. The Spectral Species Concept in Living Color
- Author
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Duccio Rocchini, Maria J. Santos, Susan L. Ustin, Jean‐Baptiste Féret, Gregory P. Asner, Carl Beierkuhnlein, Michele Dalponte, Hannes Feilhauer, Giles M. Foody, Gary N. Geller, Thomas W. Gillespie, Kate S. He, David Kleijn, Pedro J. Leitão, Marco Malavasi, Vítězslav Moudrý, Jana Müllerová, Harini Nagendra, Signe Normand, Carlo Ricotta, Michael E. Schaepman, Sebastian Schmidtlein, Andrew K. Skidmore, Petra Šímová, Michele Torresani, Philip A. Townsend, Woody Turner, Petteri Vihervaara, Martin Wegmann, Jonathan Lenoir, Rocchini, D, Santos, MJ, Ustin, SL, Feret, JB, Asner, GP, Beierkuhnlein, C, Dalponte, M, Feilhauer, H, Foody, GM, Geller, GN, Gillespie, TW, He, KS, Kleijn, D, Leitao, PJ, Malavasi, M, Moudry, V, Mullerova, J, Nagendra, H, Normand, S, Ricotta, C, Schaepman, ME, Schmidtlein, S, Skidmore, AK, Simova, P, Torresani, M, Townsend, PA, Turner, W, Vihervaara, P, Wegmann, M, and Lenoir, J
- Subjects
hyperspectral images ,Atmospheric Science ,hyperspectral image ,Geography & travel ,Soil Science ,Plant Ecology and Nature Conservation ,Aquatic Science ,ecoinformatic ,satellite imagery ,ecoinformatics ,remote sensing ,Settore BIO/07 - ECOLOGIA ,Water Science and Technology ,biodiversity ,ddc:910 ,Ecology ,vegetation communities ,plant optical type ,Paleontology ,Forestry ,airborne sensors ,plant optical types ,PE&RC ,ITC-ISI-JOURNAL-ARTICLE ,airborne sensor ,Plantenecologie en Natuurbeheer - Abstract
Biodiversity monitoring is an almost inconceivable challenge at the scale of the entire Earth. The current (and soon to be flown) generation of spaceborne and airborne optical sensors (i.e., imaging spectrometers) can collect detailed information at unprecedented spatial, temporal, and spectral resolutions. These new data streams are preceded by a revolution in modeling and analytics that can utilize the richness of these datasets to measure a wide range of plant traits, community composition, and ecosystem functions. At the heart of this framework for monitoring plant biodiversity is the idea of remotely identifying species by making use of the ‘spectral species’ concept. In theory, the spectral species concept can be defined as a species characterized by a unique spectral signature and thus remotely detectable within pixel units of a spectral image. In reality, depending on spatial resolution, pixels may contain several species which renders species-specific assignment of spectral information more challenging. The aim of this paper is to review the spectral species concept and relate it to underlying ecological principles, while also discussing the complexities, challenges and opportunities to apply this concept given current and future scientific advances in remote sensing.
- Published
- 2022
3. Mapping temperate old-growth forests in Central Europe using ALS and Sentinel-2A multispectral data.
- Author
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Adiningrat DP, Schlund M, Skidmore AK, Abdullah H, Wang T, and Heurich M
- Subjects
- Europe, Conservation of Natural Resources methods, Biodiversity, Satellite Imagery, Climate Change, Lasers, Forests, Environmental Monitoring methods, Remote Sensing Technology
- Abstract
Old-growth forests are essential to preserve biodiversity and play an important role in sequestering carbon and mitigating climate change. However, their existence across Europe is vulnerable due to the scarcity of their distribution, logging, and environmental threats. Therefore, providing the current status of old-growth forests across Europe is essential to aiding informed conservation efforts and sustainable forest management. Remote sensing techniques have proven effective for mapping and monitoring forests over large areas. However, relying solely on remote sensing spectral or structural information cannot capture comprehensive horizontal and vertical structure complexity profiles associated with old-growth forest characteristics. To overcome this issue, we combined spectral information from Sentinel-2A multispectral imagery with 3D structural information from high-density point clouds of airborne laser scanning (ALS) imagery to map old-growth forests over an extended area. Four features from the ALS data and fifteen from Sentinel-2A comprising raw band (spectral reflectance), vegetation indices (VIs), and texture were selected to create three datasets used in the classification process using the random forest algorithm. The results demonstrated that combining ALS and Sentinel-2A features improved the classification performance and yielded the highest accuracy for old-growth class, with an F1-score of 92% and producer's and user's accuracies of 93% and 90%, respectively. The findings suggest that features from ALS and Sentinel-2A data sensitive to forest structure are essential for identifying old-growth forests. Integrating open-access satellite imageries, such as Sentinel-2A and ALS data, can benefit forest managers, stakeholders, and conservationists in monitoring old-growth forest preservation across a broader spatial extent., (© 2024. The Author(s).)
- Published
- 2024
- Full Text
- View/download PDF
4. Forest top canopy bacterial communities are influenced by elevation and host tree traits.
- Author
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Duan Y, Siegenthaler A, Skidmore AK, Chariton AA, Laros I, Rousseau M, and De Groot GA
- Abstract
Background: The phyllosphere microbiome is crucial for plant health and ecosystem functioning. While host species play a determining role in shaping the phyllosphere microbiome, host trees of the same species that are subjected to different environmental conditions can still exhibit large degrees of variation in their microbiome diversity and composition. Whether these intra-specific variations in phyllosphere microbiome diversity and composition can be observed over the broader expanse of forest landscapes remains unclear. In this study, we aim to assess the variation in the top canopy phyllosphere bacterial communities between and within host tree species in the temperate European forests, focusing on Fagus sylvatica (European beech) and Picea abies (Norway spruce)., Results: We profiled the bacterial diversity, composition, driving factors, and discriminant taxa in the top canopy phyllosphere of 211 trees in two temperate forests, Veluwe National Parks, the Netherlands and Bavarian Forest National Park, Germany. We found the bacterial communities were primarily shaped by host species, and large variation existed within beech and spruce. While we showed that there was a core microbiome in all tree species examined, community composition varied with elevation, tree diameter at breast height, and leaf-specific traits (e.g., chlorophyll and P content). These driving factors of bacterial community composition also correlated with the relative abundance of specific bacterial families., Conclusions: While our results underscored the importance of host species, we demonstrated a substantial range of variation in phyllosphere bacterial diversity and composition within a host species. Drivers of these variations have implications at both the individual host tree level, where the bacterial communities differed based on tree traits, and at the broader forest landscape level, where drivers like certain highly plastic leaf traits can potentially link forest canopy bacterial community variations to forest ecosystem processes. We eventually showed close associations between forest canopy phyllosphere bacterial communities and host trees exist, and the consistent patterns emerging from these associations are critical for host plant functioning., (© 2024. The Author(s).)
- Published
- 2024
- Full Text
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5. High-throughput Soxhlet extraction method applied for analysis of leaf lignocellulose and non-structural substances.
- Author
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Torres-Rodriguez A, Darvishzadeh R, Skidmore AK, Fränzel-Luiten E, Knaken B, and Schuur B
- Abstract
The traditional Soxhlet extraction method is commonly employed to extract soluble components from non-soluble components in a solid matrix, for example, non-structural substances in biomass samples that can be separated from structural lignocellulosic compounds in biomass samples. Conventional laboratory procedures for such extractions typically involve a low sample throughput, with each run being performed individually, resulting in time-consuming and labour-intensive processes, making them impractical for analysing large sample sets. In research fields such as Earth Observation in Forest Ecosystems, extensive fieldwork sampling is required across large study areas, resulting in a substantial number of leaf samples, each with limited mass. In this study, an innovative adaptation of the conventional National Renewable Energy Laboratory (NREL) Soxhlet method is developed to create a high-throughput mini-Soxhlet apparatus that enables the simultaneous extraction of up to nineteen samples, each with a mass of 0.3 g per sample. With this adaptation, we measured the lignocellulose and extractive in 343 leaf samples collected from four temperate forest tree species. This modified approach enhances versatility and can be applied to all solid-liquid extractions and various types of vegetation tissues, such as tree leaves, shrubs, crops, feedstock, and other non-woody samples.•The solid-liquid extraction method has been implemented in a heating block facilitating 19 small flasks to measure multiple samples simultaneously while requiring only a small sample mass.•The apparatus set-up was constructed using an alumina heating block mounted on a standard laboratory heating plate. Boiling flask tubes were placed in the heating block and equipped with condenser caps and filters on glass rods on which the solid samples were placed.•The adjustments made the method suitable for application to diverse vegetation tissues and non-woody sample types. It holds particular appeal for research areas that necessitate a high sample number., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)
- Published
- 2024
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6. Habitat visibility affects the behavioral response of a large herbivore to human disturbance in forest landscapes.
- Author
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Zong X, Wang T, Skidmore AK, and Heurich M
- Subjects
- Humans, Animals, Female, Ecosystem, Forests, Predatory Behavior, Animals, Wild, Herbivory, Deer physiology
- Abstract
Wildlife can perceive humans as predators and human disturbance, whether lethal (e.g., hunting) or non-lethal (e.g., hiking, biking, and skiing), triggers antipredator behavior among prey. Visibility is the property that relates habitat structure to accessibility of visual information that allows animals to detect predators and evaluate predation risk. Thus, the visibility of a habitat (hereafter referred to as habitat visibility) for prey species alters the perceived risk of predation and therefore has a strong influence on their antipredator behavior. Yet, knowledge of how habitat visibility affects the response of animals to different types of human disturbance is limited, partly, because it is challenging to measure habitat visibility for animals at a fine spatial scale over a landscape, particularly in highly heterogeneous landscapes (e.g., forests). In this study, we employed a newly described approach that combines terrestrial and airborne LiDAR to contiguously measure fine-scale habitat visibility in a forested landscape. We applied the LiDAR-derived habitat visibility to examine how habitat visibility in forests affects the summer space use of 20 GPS-collared female red deer (Cervus elaphus) modeled with integrated step-selection functions in the Bavarian Forest National Park, Germany when exposed to various types of human disturbance including recreational activities, forest roads, hiking trails, and hunting. We found that red deer in our study area avoided areas with higher all types of human disturbance, especially during daylight hours. Furthermore, habitat visibility significantly modified the use of space by red deer in response to human recreational activities, forest roads, and hiking trails, but not to the hunting area. Red deer tended to tolerate a higher intensity of human recreational activities and to use areas closer to forest roads or hiking trails when they have lower habitat visibility (i.e., more cover). Our findings highlight the importance of considering visual perception when studying the response of wild animals to human disturbance. We emphasize the potential to mitigate negative consequences of human disturbance on wildlife, through measures such as maintaining vegetative buffers around recreational infrastructure (e.g., roads and skiing tracks) in order to reduce habitat visibility around areas frequented by humans., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)
- Published
- 2023
- Full Text
- View/download PDF
7. LiDAR reveals a preference for intermediate visibility by a forest-dwelling ungulate species.
- Author
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Zong X, Wang T, Skidmore AK, and Heurich M
- Subjects
- Animals, Female, Forests, Behavior, Animal, Movement, Ecosystem, Deer
- Abstract
Visibility (viewshed) plays a significant and diverse role in animals' behaviour and fitness. Understanding how visibility influences animal behaviour requires the measurement of habitat visibility at spatial scales commensurate to individual animal choices. However, measuring habitat visibility at a fine spatial scale over a landscape is a challenge, particularly in highly heterogeneous landscapes (e.g. forests). As a result, our ability to model the influence of fine-scale visibility on animal behaviour has been impeded or limited. In this study, we demonstrate the application of the concept of three-dimensional (3D) cumulative viewshed in the study of animal spatial behaviour at a landscape level. Specifically, we employed a newly described approach that combines terrestrial and airborne light detection and ranging (LiDAR) to measure fine-scale habitat visibility (3D cumulative viewshed) on a continuous scale in forested landscapes. We applied the LiDAR-derived visibility to investigate how visibility in forests affects the summer habitat selection and the movement of 20 GPS-collared female red deer Cervus elaphus in a temperate forest in Germany. We used integrated step selection analysis to determine whether red deer show any preference for fine-scale habitat visibility and whether visibility is related to the rate of movement of red deer. We found that red deer selected intermediate habitat visibility. Their preferred level of visibility during the day was substantially lower than that of night and twilight, whereas the preference was not significantly different between night and twilight. In addition, red deer moved faster in high-visibility areas, possibly mainly to avoid predation and anthropogenic risk. Furthermore, red deer moved most rapidly between locations in the twilight. For the first time, the preference for intermediate habitat visibility and the adaption of movement rate to fine-scale visibility by a forest-dwelling ungulate species at a landscape scale was revealed. The LiDAR technique used in this study offers fine-scale habitat visibility at the landscape level in forest ecosystems, which would be of broader interest in the fields of animal ecology and behaviour., (© 2022 The Authors. Journal of Animal Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.)
- Published
- 2023
- Full Text
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8. Deep learning enables satellite-based monitoring of large populations of terrestrial mammals across heterogeneous landscape.
- Author
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Wu Z, Zhang C, Gu X, Duporge I, Hughey LF, Stabach JA, Skidmore AK, Hopcraft JGC, Lee SJ, Atkinson PM, McCauley DJ, Lamprey R, Ngene S, and Wang T
- Subjects
- Animals, Biodiversity, Remote Sensing Technology, Mammals, Ecosystem, Deep Learning
- Abstract
New satellite remote sensing and machine learning techniques offer untapped possibilities to monitor global biodiversity with unprecedented speed and precision. These efficiencies promise to reveal novel ecological insights at spatial scales which are germane to the management of populations and entire ecosystems. Here, we present a robust transferable deep learning pipeline to automatically locate and count large herds of migratory ungulates (wildebeest and zebra) in the Serengeti-Mara ecosystem using fine-resolution (38-50 cm) satellite imagery. The results achieve accurate detection of nearly 500,000 individuals across thousands of square kilometers and multiple habitat types, with an overall F1-score of 84.75% (Precision: 87.85%, Recall: 81.86%). This research demonstrates the capability of satellite remote sensing and machine learning techniques to automatically and accurately count very large populations of terrestrial mammals across a highly heterogeneous landscape. We also discuss the potential for satellite-derived species detections to advance basic understanding of animal behavior and ecology., (© 2023. The Author(s).)
- Published
- 2023
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9. Linking the past and present to predict the distribution of Asian crested ibis (Nipponia nippon) under global changes.
- Author
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Yu F, Sun Y, Wang T, Skidmore AK, Ding C, and Ye X
- Subjects
- Humans, Animals, Ecosystem, Climate Change, Birds, Endangered Species
- Abstract
Understanding how species' ecological niches adapt to environmental changes through time is critical for predicting the effect of future global change on endangered species. Yet few studies have incorporated knowledge of past niche shifting into the assessment of species' future fate in a changing world. In this study, we integrated the ecological niche dynamics into the species distribution modeling of the Asian crested ibis (Nipponia nippon) in East Asia. Specifically, we compared historical and present ecological niches of crested ibis in four-dimensional environmental space based on species occurrence and environmental data. We then employed a multi-temporal ecological niche model to estimate the potential geographical distribution of crested ibis under future climate and land-use changes. Our results show that crested ibis retained similar though not identical ecological niches over time. Compared to the historical baseline range, the current suitable habitat for crested ibis has been reduced by 39.6%. The effects of human activity outweigh those of climate change regarding the distribution of crested ibis. We conclude that the ecological niche of crested ibis was tended to be conservative, and future potentially suitable habitat may encounter northeastward and northwestward shift, and possibly expand by 18.7% referred to the historical range. The findings of our study are of clear importance for the conservation and successful reintroduction of crested ibis in East Asia., (© 2021 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)
- Published
- 2022
- Full Text
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10. The Spectral Species Concept in Living Color.
- Author
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Rocchini D, Santos MJ, Ustin SL, Féret JB, Asner GP, Beierkuhnlein C, Dalponte M, Feilhauer H, Foody GM, Geller GN, Gillespie TW, He KS, Kleijn D, Leitão PJ, Malavasi M, Moudrý V, Müllerová J, Nagendra H, Normand S, Ricotta C, Schaepman ME, Schmidtlein S, Skidmore AK, Šímová P, Torresani M, Townsend PA, Turner W, Vihervaara P, Wegmann M, and Lenoir J
- Abstract
Biodiversity monitoring is an almost inconceivable challenge at the scale of the entire Earth. The current (and soon to be flown) generation of spaceborne and airborne optical sensors (i.e., imaging spectrometers) can collect detailed information at unprecedented spatial, temporal, and spectral resolutions. These new data streams are preceded by a revolution in modeling and analytics that can utilize the richness of these datasets to measure a wide range of plant traits, community composition, and ecosystem functions. At the heart of this framework for monitoring plant biodiversity is the idea of remotely identifying species by making use of the 'spectral species' concept. In theory, the spectral species concept can be defined as a species characterized by a unique spectral signature and thus remotely detectable within pixel units of a spectral image. In reality, depending on spatial resolution, pixels may contain several species which renders species-specific assignment of spectral information more challenging. The aim of this paper is to review the spectral species concept and relate it to underlying ecological principles, while also discussing the complexities, challenges and opportunities to apply this concept given current and future scientific advances in remote sensing., (© 2022. The Authors.)
- Published
- 2022
- Full Text
- View/download PDF
11. Author Correction: Priority list of biodiversity metrics to observe from space.
- Author
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Skidmore AK, Coops NC, Neinavaz E, Ali A, Schaepman ME, Paganini M, Kissling WD, Vihervaara P, Darvishzadeh R, Feilhauer H, Fernandez M, Fernández N, Gorelick N, Geijzendorffer I, Heiden U, Heurich M, Hobern D, Holzwarth S, Muller-Karger FE, Van De Kerchove R, Lausch A, Leitão PJ, Lock MC, Mücher CA, O'Connor B, Rocchini D, Roeoesli C, Turner W, Vis JK, Wang T, Wegmann M, and Wingate V
- Published
- 2021
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12. Priority list of biodiversity metrics to observe from space.
- Author
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Skidmore AK, Coops NC, Neinavaz E, Ali A, Schaepman ME, Paganini M, Kissling WD, Vihervaara P, Darvishzadeh R, Feilhauer H, Fernandez M, Fernández N, Gorelick N, Geijzendorffer I, Heiden U, Heurich M, Hobern D, Holzwarth S, Muller-Karger FE, Van De Kerchove R, Lausch A, Leitão PJ, Lock MC, Mücher CA, O'Connor B, Rocchini D, Roeoesli C, Turner W, Vis JK, Wang T, Wegmann M, and Wingate V
- Subjects
- Biodiversity, Benchmarking, Ecosystem
- Abstract
Monitoring global biodiversity from space through remotely sensing geospatial patterns has high potential to add to our knowledge acquired by field observation. Although a framework of essential biodiversity variables (EBVs) is emerging for monitoring biodiversity, its poor alignment with remote sensing products hinders interpolation between field observations. This study compiles a comprehensive, prioritized list of remote sensing biodiversity products that can further improve the monitoring of geospatial biodiversity patterns, enhancing the EBV framework and its applicability. The ecosystem structure and ecosystem function EBV classes, which capture the biological effects of disturbance as well as habitat structure, are shown by an expert review process to be the most relevant, feasible, accurate and mature for direct monitoring of biodiversity from satellites. Biodiversity products that require satellite remote sensing of a finer resolution that is still under development are given lower priority (for example, for the EBV class species traits). Some EBVs are not directly measurable by remote sensing from space, specifically the EBV class genetic composition. Linking remote sensing products to EBVs will accelerate product generation, improving reporting on the state of biodiversity from local to global scales.
- Published
- 2021
- Full Text
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13. rasterdiv-An Information Theory tailored R package for measuring ecosystem heterogeneity from space: To the origin and back.
- Author
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Rocchini D, Thouverai E, Marcantonio M, Iannacito M, Da Re D, Torresani M, Bacaro G, Bazzichetto M, Bernardi A, Foody GM, Furrer R, Kleijn D, Larsen S, Lenoir J, Malavasi M, Marchetto E, Messori F, Montaghi A, Moudrý V, Naimi B, Ricotta C, Rossini M, Santi F, Santos MJ, Schaepman ME, Schneider FD, Schuh L, Silvestri S, Ŝímová P, Skidmore AK, Tattoni C, Tordoni E, Vicario S, Zannini P, and Wegmann M
- Abstract
Ecosystem heterogeneity has been widely recognized as a key ecological indicator of several ecological functions, diversity patterns and change, metapopulation dynamics, population connectivity or gene flow.In this paper, we present a new R package-rasterdiv-to calculate heterogeneity indices based on remotely sensed data. We also provide an ecological application at the landscape scale and demonstrate its power in revealing potentially hidden heterogeneity patterns.The rasterdiv package allows calculating multiple indices, robustly rooted in Information Theory, and based on reproducible open-source algorithms., (© 2021 The Authors. Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society.)
- Published
- 2021
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14. Worsening of tree-related public health issues under climate change.
- Author
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Jia P, Wang T, van Vliet AJH, Skidmore AK, and van Aalst M
- Subjects
- Animals, Forests, Humans, Population Dynamics, Climate Change, Moths, Public Health, Trees physiology
- Published
- 2020
- Full Text
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15. Comment on "The global tree restoration potential".
- Author
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Skidmore AK, Wang T, de Bie K, and Pilesjö P
- Subjects
- Carbon, Humans, Forests, Trees
- Abstract
Bastin et al (Reports, 5 July 2019, p. 76) claim that 205 gigatonnes of carbon can be globally sequestered by restoring 0.9 billion hectares of forest and woodland canopy cover. Reinterpreting the data from Bastin et al , we show that the global land area actually required to sequester human-emitted CO
2 is at least a factor of 3 higher, representing an unrealistically large area., (Copyright © 2019, American Association for the Advancement of Science.)- Published
- 2019
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16. Heavy metal pollution at mine sites estimated from reflectance spectroscopy following correction for skewed data.
- Author
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Sun W, Skidmore AK, Wang T, and Zhang X
- Subjects
- Calibration, Environmental Pollution statistics & numerical data, Least-Squares Analysis, Soil chemistry, Spectrum Analysis, Environmental Monitoring methods, Metals, Heavy analysis, Mining, Soil Pollutants analysis
- Abstract
The heavy metal concentration of soil samples often exhibits a skewed distribution, especially for soil samples from mining areas with an extremely high concentration of heavy metals. In this study, to model soil contamination in mining areas using reflectance spectroscopy, the skewed distribution was corrected and heavy metal concentration estimated. In total, 46 soil samples from a mining area, along with corresponding field soil spectra, were collected. Laboratory spectra of the soil samples and the field spectra were used to estimate copper (Cu) concentration in the mining area. A logarithmic transformation was used to correct the skewed distribution, and based on the sorption of Cu on spectrally active soil constituents, the spectral bands associated with iron oxides were extracted from the visible and near-infrared (VNIR) region and used in the estimation. A genetic algorithm was adopted for band selection, and partial least squares regression was used to calibrate the estimation model. After transforming the distribution of Cu concentration, the accuracies (R
2 ) of the estimation of Cu concentration using laboratory and field spectra separately were 0.94 and 0.96. The results indicate that Cu concentration in the mining area can be estimated using reflectance spectroscopy following correction of skewed distribution., (Copyright © 2019 Elsevier Ltd. All rights reserved.)- Published
- 2019
- Full Text
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17. Identifying rice stress on a regional scale from multi-temporal satellite images using a Bayesian method.
- Author
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Liu M, Wang T, Skidmore AK, Liu X, and Li M
- Subjects
- Bayes Theorem, China, Crops, Agricultural, Environmental Pollution analysis, Humans, Metals, Heavy analysis, Soil, Stress, Physiological physiology, Environmental Monitoring methods, Environmental Pollution statistics & numerical data, Oryza physiology, Satellite Imagery, Soil Pollutants analysis
- Abstract
Crops are prone to various types of stress, such as caused by heavy metals, drought and pest/disease, during their life cycle. Heavy metal stress in crops poses a serious threat to crop quality and human health. However, differentiating between heavy metal and non-heavy metal stress presents a great challenge, since responses to environmental stress in crops are complex and uncertain, with different stressors possibly triggering similar canopy reflectance responses. This study aims to infer the occurrence probability of heavy metal stress (i.e., Cd stress) on a regional scale by integrating satellite-derived vegetation index and spatio-temporal characteristics of different stressors with a Bayesian method. The study area is located in the Hunan Province, China. Seven scenes of Sentinel-2 satellite images from 2016 to 2017 were collected, as well as Cd concentrations in the soil. First, the probability of rice being stressed was screened using the normalized difference red-edge index (NDRE) at all the growth stages of rice. Further, the stressed rice was used as input, along with the coefficients of spatio-temporal variation (CSTV) derived from NDRE, for a Bayesian method to infer rice exposed to Cd pollution. The results demonstrated that NDRE was a sensitive indicator for assessing stress levels in rice crops. The CSTV with a threshold of 2.7 successfully detected rice under Cd as well as abrupt stress on a regional scale. A high map accuracy for Cd induced stress in rice was achieved with an accuracy of 81.57%. This study suggests that vegetation index obtained from satellite images can assist in capturing crop stress, and that the used Bayesian method can be very useful for distinguishing a specific stressor in crops by incorporating temporal-spatial characteristic of different stressors in crops into satellite-derived vegetation index., (Copyright © 2019 Elsevier Ltd. All rights reserved.)
- Published
- 2019
- Full Text
- View/download PDF
18. Climate and land use changes will degrade the distribution of Rhododendrons in China.
- Author
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Yu F, Wang T, Groen TA, Skidmore AK, Yang X, Ma K, and Wu Z
- Subjects
- China, Biodiversity, Climate Change, Conservation of Natural Resources, Plant Dispersal, Rhododendron physiology
- Abstract
Biodiversity loss and variation in species responses to climate and land use change have been found across broad taxonomic groups. However, whether species from the same taxonomic group with distinct geographical ranges will respond differently is poorly understood. The aim of this study is to predict the potential impacts of future climate and land use change on the distribution of narrow- and wide-ranging Rhododendron species, and estimate their relative contribution in China. We applied the presence-only ecological niche model MaxEnt to predict the distribution of 10 narrow-ranging and 10 wide-ranging Rhododendron species for the year 2070, using three general circulation models and three scenarios of climate and land use change. We measured the predicted distribution change of each species using change ratio, distance and direction of core range shifts, and niche overlap using Schoener's D. We found that the distribution areas of six narrow-ranging species would decrease, of which one species would go extinct. The remaining four narrow-ranging species would experience range expansion. Distribution of all the wide-ranging Rhododendron species would decrease. All Rhododendrons will shift to the northwest. We conclude that Rhododendron species generally will be negatively affected by the climatic and land use change expected in 2070 from the three scenarios evaluated in this study, but some narrow-ranging species may be positively influenced. Narrow-ranging Rhododendron species are more vulnerable compared to wide-ranging Rhododendron species. This study demonstrated that the effects of climate and land use change on alpine and subalpine plant species is species-specific, thereby strengthening our understanding of the impacts of climate and land use change on plant distribution., (Copyright © 2018. Published by Elsevier B.V.)
- Published
- 2019
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19. Heavy metal-induced stress in rice crops detected using multi-temporal Sentinel-2 satellite images.
- Author
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Liu M, Wang T, Skidmore AK, and Liu X
- Subjects
- China, Crops, Agricultural drug effects, Humans, Oryza drug effects, Soil, Crops, Agricultural physiology, Environmental Monitoring methods, Metals, Heavy toxicity, Oryza physiology, Satellite Imagery, Soil Pollutants toxicity, Stress, Physiological
- Abstract
Regional-level information on heavy metal pollution in agro-ecosystems is essential for food security because excessive levels of heavy metals in crops may pose risks to humans. However, collecting this information over large areas is inherently costly. This paper investigates the possibility of applying multi-temporal Sentinel-2 satellite images to detect heavy metal-induced stress (i.e., Cd stress) in rice crops in four study areas in Zhuzhou City, Hunan Province, China. For this purpose, we compared seven Sentinel-2 images acquired in 2016 and 2017 with in situ measured hyper-spectral data, chlorophyll content, rice leaf area index, and heavy metal concentrations in soil collected from 2014 to 2017. Vegetation indices (VIs) related to red edge bands were referred to as the sensitive indicators for screening stressed rice from unstressed rice. The coefficients of spatio-temporal variation (CSTV) derived from the VIs allowed us to discriminate crops exposed to pollution from heavy metals as well as environmental stressors. The results indicate that (i) the red edge chlorophyll index, the red edge position index, and the normalized difference red edge 2 index derived from multi-temporal Sentinel-2 images were good indicators for screening stressed rice from unstressed rice; (ii) Rice under Cd stress remained stable with lower CSTV values of VIs overall growth stages in the experimental region, whereas rice under other stressors (i.e., pests and disease) showed abrupt changes at some growth stages and presented "hot spots" with greater CSTV values; and (iii) the proposed spatio-temporal anomaly detection method was successful at detecting rice under Cd stress; and CSTVs of rice VIs stabilized regardless of whether they were applied to consecutive growth stages or to two different crop years. This study suggests that regional heavy metal stress may be accurately detected using multi-temporal Sentinel-2 images, using VIs sensitive to the spatio-temporal characteristics of crops., (Copyright © 2018 Elsevier B.V. All rights reserved.)
- Published
- 2018
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20. Free satellite data key to conservation.
- Author
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Buchanan GM, Beresford AE, Hebblewhite M, Escobedo FJ, De Klerk HM, Donald PF, Escribano P, Koh LP, Martínez-López J, Pettorelli N, Skidmore AK, Szantoi Z, Tabor K, Wegmann M, and Wich S
- Subjects
- Biodiversity, Conservation of Natural Resources, Environmental Monitoring, Satellite Imagery
- Published
- 2018
- Full Text
- View/download PDF
21. Building essential biodiversity variables (EBVs) of species distribution and abundance at a global scale.
- Author
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Kissling WD, Ahumada JA, Bowser A, Fernandez M, Fernández N, García EA, Guralnick RP, Isaac NJB, Kelling S, Los W, McRae L, Mihoub JB, Obst M, Santamaria M, Skidmore AK, Williams KJ, Agosti D, Amariles D, Arvanitidis C, Bastin L, De Leo F, Egloff W, Elith J, Hobern D, Martin D, Pereira HM, Pesole G, Peterseil J, Saarenmaa H, Schigel D, Schmeller DS, Segata N, Turak E, Uhlir PF, Wee B, and Hardisty AR
- Subjects
- Animals, Models, Biological, Animal Distribution physiology, Biodiversity, Environmental Monitoring methods
- Abstract
Much biodiversity data is collected worldwide, but it remains challenging to assemble the scattered knowledge for assessing biodiversity status and trends. The concept of Essential Biodiversity Variables (EBVs) was introduced to structure biodiversity monitoring globally, and to harmonize and standardize biodiversity data from disparate sources to capture a minimum set of critical variables required to study, report and manage biodiversity change. Here, we assess the challenges of a 'Big Data' approach to building global EBV data products across taxa and spatiotemporal scales, focusing on species distribution and abundance. The majority of currently available data on species distributions derives from incidentally reported observations or from surveys where presence-only or presence-absence data are sampled repeatedly with standardized protocols. Most abundance data come from opportunistic population counts or from population time series using standardized protocols (e.g. repeated surveys of the same population from single or multiple sites). Enormous complexity exists in integrating these heterogeneous, multi-source data sets across space, time, taxa and different sampling methods. Integration of such data into global EBV data products requires correcting biases introduced by imperfect detection and varying sampling effort, dealing with different spatial resolution and extents, harmonizing measurement units from different data sources or sampling methods, applying statistical tools and models for spatial inter- or extrapolation, and quantifying sources of uncertainty and errors in data and models. To support the development of EBVs by the Group on Earth Observations Biodiversity Observation Network (GEO BON), we identify 11 key workflow steps that will operationalize the process of building EBV data products within and across research infrastructures worldwide. These workflow steps take multiple sequential activities into account, including identification and aggregation of various raw data sources, data quality control, taxonomic name matching and statistical modelling of integrated data. We illustrate these steps with concrete examples from existing citizen science and professional monitoring projects, including eBird, the Tropical Ecology Assessment and Monitoring network, the Living Planet Index and the Baltic Sea zooplankton monitoring. The identified workflow steps are applicable to both terrestrial and aquatic systems and a broad range of spatial, temporal and taxonomic scales. They depend on clear, findable and accessible metadata, and we provide an overview of current data and metadata standards. Several challenges remain to be solved for building global EBV data products: (i) developing tools and models for combining heterogeneous, multi-source data sets and filling data gaps in geographic, temporal and taxonomic coverage, (ii) integrating emerging methods and technologies for data collection such as citizen science, sensor networks, DNA-based techniques and satellite remote sensing, (iii) solving major technical issues related to data product structure, data storage, execution of workflows and the production process/cycle as well as approaching technical interoperability among research infrastructures, (iv) allowing semantic interoperability by developing and adopting standards and tools for capturing consistent data and metadata, and (v) ensuring legal interoperability by endorsing open data or data that are free from restrictions on use, modification and sharing. Addressing these challenges is critical for biodiversity research and for assessing progress towards conservation policy targets and sustainable development goals., (© 2017 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society.)
- Published
- 2018
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22. Impacts of future climate and land cover changes on threatened mammals in the semi-arid Chinese Altai Mountains.
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Ye X, Yu X, Yu C, Tayibazhaer A, Xu F, Skidmore AK, and Wang T
- Subjects
- Animals, China, Biodiversity, Climate Change, Conservation of Natural Resources, Endangered Species, Mammals
- Abstract
Dryland biodiversity plays important roles in the fight against desertification and poverty, but is highly vulnerable to the impacts of environmental change. However, little research has been conducted on dual pressure from climate and land cover changes on biodiversity in arid and semi-arid environments. Concequntly, it is crutial to understand the potential impacts of future climate and land cover changes on dryland biodiversity. Here, using the Chinese Altai Mountains as a case study area, we predicted the future spatial distributions and local assemblages of nine threatened mammal species under projected climate and land cover change scenarios for the period 2010-2050. The results show that remarkable declines in mammal species richness as well as high rates of species turnover are seen to occur across large areas in the Chinese Altai Mountains, highlighting an urgent need for developing protection strategies for areas outside of current nature reserve network. The selected mammals are predicted to lose more than 50% of their current ranges on average, which is much higher than species' range gains (around 15%) under future climate and land cover changes. Most of the species are predicted to contract their ranges while moving eastwards and to higher altitudes, raising the need for establishing cross-border migration pathways for species. Furthermore, the inclusion of land cover changes had notable effects on projected range shifts of individual species under climate changes, demonstrating that land cover changes should be incorporated into the assessment of future climate impacts to facilitate biodiversity conservation in arid and semi-arid environments., (Copyright © 2017 Elsevier B.V. All rights reserved.)
- Published
- 2018
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23. Identification of Griffon Vulture's Flight Types Using High-Resolution Tracking Data.
- Author
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Khosravifard S, Venus V, Skidmore AK, Bouten W, Muñoz AR, and Toxopeus AG
- Abstract
Being one of the most frequently killed raptors by collision with wind turbines, little is known about the Griffon vulture's flight strategies and behaviour in a fine scale. In this study, we used high-resolution tracking data to differentiate between the most frequently observed flight types of the Griffon, and evaluated the performance of our proposed approach by an independent observation during a period of 4 weeks of fieldwork. Five passive flight types including three types of soaring and two types of gliding were discriminated using the patterns of measured GPS locations. Of all flight patterns, gliding was classified precisely (precision = 88%), followed by linear and thermal soaring with precision of 83 and 75%, respectively. The overall accuracy of our classification was 70%. Our study contributes a baseline technique using high-resolution tracking data for the classification of flight types, and is one step forward towards the collision management of this species., Competing Interests: All data generated and/or analysed during the current study are available from the corresponding author on reasonable request.The authors declare that they have no competing interests.The experimental procedures of this study, including bird trapping and GPS tagging, were approved by the Consejería de Medio Ambiente of the Junta de Andalucía, who provided permissions for this research through the licence to capture and mark raptors to Antonio-Román Muñoz (Regional Licence: 65029 Consejería de Agricultura, Pesca y Medio Ambiente, Junta de Andalucía; National Licence 650038, Ministerio de Agricultura, Alimentation y Medio Ambiente).
- Published
- 2018
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24. PhD thesis: Avoid bias against junior researchers.
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Skidmore AK
- Subjects
- Bias, Humans, Nursing Research, Research Personnel
- Published
- 2016
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25. Decline of traditional rice farming constrains the recovery of the endangered Asian crested ibis (Nipponia nippon).
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Sun Y, Wang T, Skidmore AK, Wang Q, and Ding C
- Subjects
- Animals, China, Ecosystem, Population Dynamics, Agriculture, Birds physiology, Conservation of Natural Resources, Endangered Species, Oryza growth & development
- Abstract
Traditional agriculture benefits a rich diversity of plants and animals. The winter-flooded rice fields in the Qinling Mountains, China, are the last refuge for the endangered Asian crested ibis (Nipponia nippon), and intensive efforts have been made to protect this anthropogenic habitat. Analyses of multi-temporal satellite data indicate that winter-flooded rice fields have been continuously reduced across the current range of crested ibis during the past two decades. The rate of loss of these fields in the core-protected areas has unexpectedly increased to a higher level than that in non-protected areas in the past decade. The best fit (R (2) = 0.87) numerical response model of the crested ibis population shows that a reduction of winter-flooded rice fields decreases population growth and predicts that the population growth will be constrained by the decline of traditional winter-flooded rice fields in the coming decades. Our findings suggest that the decline of traditional rice farming is likely to continue to pose a threat to the long-term survival and recovery of the crested ibis population in China.
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- 2015
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26. Using Poaching Levels and Elephant Distribution to Assess the Conservation Efficacy of Private, Communal and Government Land in Northern Kenya.
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Ihwagi FW, Wang T, Wittemyer G, Skidmore AK, Toxopeus AG, Ngene S, King J, Worden J, Omondi P, and Douglas-Hamilton I
- Subjects
- Animals, Crime statistics & numerical data, Demography, Government Programs, Kenya, Program Evaluation, Conservation of Natural Resources methods, Conservation of Natural Resources statistics & numerical data, Elephants
- Abstract
Efforts to curb elephant poaching have focused on reducing demand, confiscating ivory and boosting security patrols in elephant range. Where land is under multiple uses and ownership, determining the local poaching dynamics is important for identifying successful conservation models. Using 2,403 verified elephant, Loxodonta africana, mortality records collected from 2002 to 2012 and the results of aerial total counts of elephants conducted in 2002, 2008 and 2012 for the Laikipia-Samburu ecosystem of northern Kenya, we sought to determine the influence of land ownership and use on diurnal elephant distribution and on poaching levels. We show that the annual proportions of illegally killed (i.e., poached) elephants increased over the 11 years of the study, peaking at 70% of all recorded deaths in 2012. The type of land use was more strongly related to levels of poaching than was the type of ownership. Private ranches, comprising only 13% of land area, hosted almost half of the elephant population and had significantly lower levels of poaching than other land use types except for the officially designated national reserves (covering only 1.6% of elephant range in the ecosystem). Communal grazing lands hosted significantly fewer elephants than expected, but community areas set aside for wildlife demonstrated significantly higher numbers of elephants and lower illegal killing levels relative to non-designated community lands. While private lands had lower illegal killing levels than community conservancies, the success of the latter relative to other community-held lands shows the importance of this model of land use for conservation. This work highlights the relationship between illegal killing and various land ownership and use models, which can help focus anti-poaching activities.
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- 2015
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27. Environmental science: Agree on biodiversity metrics to track from space.
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Skidmore AK, Pettorelli N, Coops NC, Geller GN, Hansen M, Lucas R, Mücher CA, O'Connor B, Paganini M, Pereira HM, Schaepman ME, Turner W, Wang T, and Wegmann M
- Subjects
- Animals, Conservation of Natural Resources methods, Ecological Parameter Monitoring instrumentation, Ecology instrumentation, Ecology standards, Environmental Policy, Biodiversity, Ecological Parameter Monitoring methods, Ecology methods, Satellite Imagery
- Published
- 2015
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28. How do two giant panda populations adapt to their habitats in the Qinling and Qionglai Mountains, China.
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Liu X, Wang T, Wang T, Skidmore AK, and Songer M
- Subjects
- Animals, Behavior, Animal physiology, China, Conservation of Natural Resources, Female, Male, Movement, Seasons, Spatial Analysis, Adaptation, Physiological, Altitude, Ecosystem, Ursidae physiology
- Abstract
The spatial separation of the Qinling Mountains from the western mountains has caused morphological and genetic distinctions of giant pandas. Could this separation also cause the pandas' behavior change? In this research, we focused on the pandas' movement pattern and selected two wild panda groups in Foping and Wolong Nature Reserves (NR) to represent the populations in the Qinling and Qionglai Mountains, respectively. We hypothesized that the Qinling pandas have developed a different seasonal movement pattern compared with the pandas in the western mountains. We analyzed the radio tracking data from two NRs by using GIS. Our results showed the following significant differences: (1) The Foping pandas live most of the year in the low elevation areas and move higher during June and remain through August while the Wolong pandas live most of the year in the high elevation areas and move lower in April and stay through June; (2) Comparing their low and high elevational areas shows the distinct spatial patterns between reserves, forming two obviously separated clusters in Foping but a single-compact cluster in Wolong; (3) Foping pandas move an average of 425 m ± 147 s.d. daily, while Wolong pandas move an average of 550 m ± 343 s.d. daily; and (4) Three habitat factors (i.e., terrain, temperature, and bamboo nutrient) were taken as the driving forces and analyzed, and they showed a strong support explanation to these different movement behaviors of pandas in two NRs. Our findings have important implications for management, for instance, it needs to be careful considering the behavior difference of the pandas when reintroducing them to the wild.
- Published
- 2015
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29. Spotting East African mammals in open savannah from space.
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Yang Z, Wang T, Skidmore AK, de Leeuw J, Said MY, and Freer J
- Subjects
- Africa, Eastern, Animals, Kenya, Mammals, Photography, Space Flight, Censuses, Image Processing, Computer-Assisted methods, Population Dynamics statistics & numerical data, Satellite Imagery methods
- Abstract
Knowledge of population dynamics is essential for managing and conserving wildlife. Traditional methods of counting wild animals such as aerial survey or ground counts not only disturb animals, but also can be labour intensive and costly. New, commercially available very high-resolution satellite images offer great potential for accurate estimates of animal abundance over large open areas. However, little research has been conducted in the area of satellite-aided wildlife census, although computer processing speeds and image analysis algorithms have vastly improved. This paper explores the possibility of detecting large animals in the open savannah of Maasai Mara National Reserve, Kenya from very high-resolution GeoEye-1 satellite images. A hybrid image classification method was employed for this specific purpose by incorporating the advantages of both pixel-based and object-based image classification approaches. This was performed in two steps: firstly, a pixel-based image classification method, i.e., artificial neural network was applied to classify potential targets with similar spectral reflectance at pixel level; and then an object-based image classification method was used to further differentiate animal targets from the surrounding landscapes through the applications of expert knowledge. As a result, the large animals in two pilot study areas were successfully detected with an average count error of 8.2%, omission error of 6.6% and commission error of 13.7%. The results of the study show for the first time that it is feasible to perform automated detection and counting of large wild animals in open savannahs from space, and therefore provide a complementary and alternative approach to the conventional wildlife survey techniques.
- Published
- 2014
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30. Eutrophication of mangroves linked to depletion of foliar and soil base cations.
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Fauzi A, Skidmore AK, Heitkönig IM, van Gils H, and Schlerf M
- Subjects
- Cations analysis, Ecosystem, Eutrophication, Indonesia, Nitrogen analysis, Plant Leaves chemistry, Environmental Monitoring, Rhizophoraceae physiology, Soil chemistry, Wetlands
- Abstract
There is growing concern that increasing eutrophication causes degradation of coastal ecosystems. Studies in terrestrial ecosystems have shown that increasing the concentration of nitrogen in soils contributes to the acidification process, which leads to leaching of base cations. To test the effects of eutrophication on the availability of base cations in mangroves, we compared paired leaf and soil nutrient levels sampled in Nypa fruticans and Rhizophora spp. on a severely disturbed, i.e. nutrient loaded, site (Mahakam delta) with samples from an undisturbed, near-pristine site (Berau delta) in East Kalimantan, Indonesia. The findings indicate that under pristine conditions, the availability of base cations in mangrove soils is determined largely by salinity. Anthropogenic disturbances on the Mahakam site have resulted in eutrophication, which is related to lower levels of foliar and soil base cations. Path analysis suggests that increasing soil nitrogen reduces soil pH, which in turn reduces the levels of foliar and soil base cations in mangroves.
- Published
- 2014
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31. Migratory herbivorous waterfowl track satellite-derived green wave index.
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Shariatinajafabadi M, Wang T, Skidmore AK, Toxopeus AG, Kölzsch A, Nolet BA, Exo KM, Griffin L, Stahl J, and Cabot D
- Subjects
- Altitude, Analysis of Variance, Animals, Biomass, Food Supply, Greenland, Least-Squares Analysis, Models, Biological, Russia, Seasons, Svalbard, Animal Migration, Geese physiology, Herbivory physiology, Plants, Spacecraft
- Abstract
Many migrating herbivores rely on plant biomass to fuel their life cycles and have adapted to following changes in plant quality through time. The green wave hypothesis predicts that herbivorous waterfowl will follow the wave of food availability and quality during their spring migration. However, testing this hypothesis is hampered by the large geographical range these birds cover. The satellite-derived normalized difference vegetation index (NDVI) time series is an ideal proxy indicator for the development of plant biomass and quality across a broad spatial area. A derived index, the green wave index (GWI), has been successfully used to link altitudinal and latitudinal migration of mammals to spatio-temporal variations in food quality and quantity. To date, this index has not been used to test the green wave hypothesis for individual avian herbivores. Here, we use the satellite-derived GWI to examine the green wave hypothesis with respect to GPS-tracked individual barnacle geese from three flyway populations (Russian n = 12, Svalbard n = 8, and Greenland n = 7). Data were collected over three years (2008-2010). Our results showed that the Russian and Svalbard barnacle geese followed the middle stage of the green wave (GWI 40-60%), while the Greenland geese followed an earlier stage (GWI 20-40%). Despite these differences among geese populations, the phase of vegetation greenness encountered by the GPS-tracked geese was close to the 50% GWI (i.e. the assumed date of peak nitrogen concentration), thereby implying that barnacle geese track high quality food during their spring migration. To our knowledge, this is the first time that the migration of individual avian herbivores has been successfully studied with respect to vegetation phenology using the satellite-derived GWI. Our results offer further support for the green wave hypothesis applying to long-distance migrants on a larger scale.
- Published
- 2014
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32. Joint effects of habitat heterogeneity and species' life-history traits on population dynamics in spatially structured landscapes.
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Ye X, Skidmore AK, and Wang T
- Subjects
- Animal Distribution, Animals, Models, Biological, Models, Statistical, Population Dynamics, Statistics, Nonparametric, Conservation of Natural Resources, Ecosystem
- Abstract
Both habitat heterogeneity and species' life-history traits play important roles in driving population dynamics, yet there is little scientific consensus around the combined effect of these two factors on populations in complex landscapes. Using a spatially explicit agent-based model, we explored how interactions between habitat spatial structure (defined here as the scale of spatial autocorrelation in habitat quality) and species life-history strategies (defined here by species environmental tolerance and movement capacity) affect population dynamics in spatially heterogeneous landscapes. We compared the responses of four hypothetical species with different life-history traits to four landscape scenarios differing in the scale of spatial autocorrelation in habitat quality. The results showed that the population size of all hypothetical species exhibited a substantial increase as the scale of spatial autocorrelation in habitat quality increased, yet the pattern of population increase was shaped by species' movement capacity. The increasing scale of spatial autocorrelation in habitat quality promoted the resource share of individuals, but had little effect on the mean mortality rate of individuals. Species' movement capacity also determined the proportion of individuals in high-quality cells as well as the proportion of individuals experiencing competition in response to increased spatial autocorrelation in habitat quality. Positive correlations between the resource share of individuals and the proportion of individuals experiencing competition indicate that large-scale spatial autocorrelation in habitat quality may mask the density-dependent effect on populations through increasing the resource share of individuals, especially for species with low mobility. These findings suggest that low-mobility species may be more sensitive to habitat spatial heterogeneity in spatially structured landscapes. In addition, localized movement in combination with spatial autocorrelation may increase the population size, despite increased density effects.
- Published
- 2014
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33. Reduced dependence of Crested Ibis on winter-flooded rice fields: implications for their conservation.
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Sun Y, Skidmore AK, Wang T, van Gils HA, Wang Q, Qing B, and Ding C
- Subjects
- Animals, China, Conservation of Natural Resources, Ecosystem, Geography, Spatial Analysis, Birds, Nesting Behavior, Oryza, Seasons
- Abstract
The Crested Ibis Nipponia nippon was once thought to be extinct in the wild until seven birds were discovered in a remote mountain village in China in 1981. Studies suggested that winter-flooded rice fields play an essential role in nest site selection by the Crested Ibis and hence in their survival. Considerable efforts were therefore made to conserve the winter-flooded rice fields, but these have caused conflicts between the agricultural and conservation communities. The population and geographical range of the wild Crested Ibis has expanded greatly since 1981, but there is no spatial information on the winter-flooded rice fields, nor on the current association of nest sites and winter-flooded rice fields. We mapped winter-flooded rice fields across the entire current range of Crested Ibis using innovative remote sensing and geographical information systems (GIS) techniques. The spatial relationships between the nest site clusters and winter-flooded rice fields were quantified using Ward's hierarchical clustering method and Ripley's K-function. We show that both have significantly clumped distribution patterns and that they are positively associated. However, the dependence of Crested Ibis on the winter-flooded rice fields varied significantly among the nest site clusters and has decreased over the years, indicating the absence of winter-flooded rice fields is not constraining their recovery and population expansion. We therefore recommend that efforts should be made to protect the existing winter-flooded rice fields and to restore the functionality of natural and semi-natural wetlands, to encourage both in-situ conservation and the re-introduction of the Crested Ibis. In addition, we recommend that caution should be exercised when interpreting the habitat requirements of species with a narrow distribution, particularly when that interpretation is based only on their current habitat.
- Published
- 2014
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34. Smallholder farms as stepping stone corridors for crop-raiding elephant in northern Tanzania: integration of Bayesian expert system and network simulator.
- Author
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Pittiglio C, Skidmore AK, van Gils HA, McCall MK, and Prins HH
- Subjects
- Animals, Ecosystem, Tanzania, Behavior, Animal, Crops, Agricultural, Elephants psychology
- Abstract
Crop-raiding elephants affect local livelihoods, undermining conservation efforts. Yet, crop-raiding patterns are poorly understood, making prediction and protection difficult. We hypothesized that raiding elephants use corridors between daytime refuges and farmland. Elephant counts, crop-raiding records, household surveys, Bayesian expert system, and least-cost path simulation were used to predict four alternative categories of daily corridors: (1) footpaths, (2) dry river beds, (3) stepping stones along scattered small farms, and (4) trajectories of shortest distance to refuges. The corridor alignments were compared in terms of their minimum cumulative resistance to elephant movement and related to crop-raiding zones quantified by a kernel density function. The "stepping stone" corridors predicted the crop-raiding patterns. Elephant presence was confirmed along these corridors, demonstrating that small farms located between refuges and contiguous farmland increase habitat connectivity for elephant. Our analysis successfully predicted elephant occurrence in farmland where daytime counts failed to detect nocturnal presence. These results have conservation management implications.
- Published
- 2014
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35. Elephant movement closely tracks precipitation-driven vegetation dynamics in a Kenyan forest-savanna landscape.
- Author
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Bohrer G, Beck PS, Ngene SM, Skidmore AK, and Douglas-Hamilton I
- Abstract
Background: This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation. Movement data were acquired for five bachelors and five female family herds during three years in the Marsabit protected area in Kenya and changes in vegetation were mapped using MODIS normalized difference vegetation index time series (NDVI). In the study area, elevations of 650 to 1100 m.a.s.l experience two growth periods per year, while above 1100 m.a.s.l. growth periods last a year or longer., Results: We find that elephants respond quickly to changes in forage and water availability, making migrations in response to both large and small rainfall events. The elevational migration of individual elephants closely matched the patterns of greening and senescing of vegetation in their home range. Elephants occupied lower elevations when vegetation activity was high, whereas they retreated to the evergreen forest at higher elevations while vegetation senesced. Elephant home ranges decreased in size, and overlapped less with increasing elevation., Conclusions: A recent hypothesis that ungulate migrations in savannas result from countervailing seasonally driven rainfall and fertility gradients is demonstrated, and extended to shorter-distance migrations. In other words, the trade-off between the poor forage quality and accessibility in the forest with its year-round water sources on the one hand and the higher quality forage in the low-elevation scrubland with its seasonal availability of water on the other hand, drives the relatively short migrations (the two main corridors are 20 and 90 km) of the elephants. In addition, increased intra-specific competition appears to influence the animals' habitat use during the dry season indicating that the human encroachment on the forest is affecting the elephant population.
- Published
- 2014
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36. Shrimp pond effluent dominates foliar nitrogen in disturbed mangroves as mapped using hyperspectral imagery.
- Author
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Fauzi A, Skidmore AK, van Gils H, Schlerf M, and Heitkönig IM
- Subjects
- Animals, Eutrophication, Penaeidae, Remote Sensing Technology, Aquaculture, Environmental Monitoring methods, Nitrogen analysis, Water Pollutants, Chemical analysis, Wetlands
- Abstract
Conversion of mangroves to shrimp ponds creates fragmentation and eutrophication. Detection of the spatial variation of foliar nitrogen is essential for understanding the effect of eutrophication on mangroves. We aim (i) to estimate nitrogen variability across mangrove landscapes of the Mahakam delta using airborne hyperspectral remote sensing (HyMap) and (ii) to investigate links between the variation of foliar nitrogen mapped and local environmental variables. In this study, multivariate prediction models achieved a higher level of accuracy than narrow-band vegetation indices, making multivariate modeling the best choice for mapping. The variation of foliar nitrogen concentration in mangroves was significantly influenced by the local environment: (1) position of mangroves (seaward/landward), (2) distance to the shrimp ponds, and (3) predominant mangrove species. The findings suggest that anthropogenic disturbances, in this case shrimp ponds, influence nitrogen variation in mangroves. Mangroves closer to the shrimp ponds had higher foliar nitrogen concentrations., (Copyright © 2013 Elsevier Ltd. All rights reserved.)
- Published
- 2013
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37. Sensing solutions for collecting spatio-temporal data for wildlife monitoring applications: a review.
- Author
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Baratchi M, Meratnia N, Havinga PJ, Skidmore AK, and Toxopeus BA
- Subjects
- Animals, Computer Communication Networks, Animals, Wild physiology, Data Collection methods, Remote Sensing Technology methods, Spatio-Temporal Analysis
- Abstract
Movement ecology is a field which places movement as a basis for understanding animal behavior. To realize this concept, ecologists rely on data collection technologies providing spatio-temporal data in order to analyze movement. Recently, wireless sensor networks have offered new opportunities for data collection from remote places through multi-hop communication and collaborative capability of the nodes. Several technologies can be used in such networks for sensing purposes and for collecting spatio-temporal data from animals. In this paper, we investigate and review technological solutions which can be used for collecting data for wildlife monitoring. Our aim is to provide an overview of different sensing technologies used for wildlife monitoring and to review their capabilities in terms of data they provide for modeling movement behavior of animals.
- Published
- 2013
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38. Tracing glacial refugia of Triturus newts based on mitochondrial DNA phylogeography and species distribution modeling.
- Author
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Wielstra B, Crnobrnja-Isailović J, Litvinchuk SN, Reijnen BT, Skidmore AK, Sotiropoulos K, Toxopeus AG, Tzankov N, Vukov T, and Arntzen JW
- Abstract
Introduction: The major climatic oscillations during the Quaternary Ice Age heavily influenced the distribution of species and left their mark on intraspecific genetic diversity. Past range shifts can be reconstructed with the aid of species distribution modeling and phylogeographical analyses. We test the responses of the different members of the genus Triturus (i.e. the marbled and crested newts) as the climate shifted from the previous glacial period (the Last Glacial Maximum, ~21 Ka) to the current interglacial., Results: We present the results of a dense mitochondrial DNA phylogeography (visualizing genetic diversity within and divergence among populations) and species distribution modeling (using two different climate simulations) for the nine Triturus species on composite maps., Conclusions: The combined use of species distribution modeling and mitochondrial phylogeography provides insight in the glacial contraction and postglacial expansion of Triturus. The combined use of the two independent techniques yields a more complete understanding of the historical biogeography of Triturus than both approaches would on their own. Triturus newts generally conform to the 'southern richness and northern purity' paradigm, but we also find more intricate patterns, such as the absence of genetic variation and suitable area at the Last Glacial Maximum (T. dobrogicus), an 'extra-Mediterranean' refugium in the Carpathian Basin (T. cristatus), and areas where species displaced one another postglacially (e.g. T. macedonicus and western T. karelinii). We provide a biogeographical scenario for Triturus, showing the positions of glacial refugia, the regions that were postglacially colonized and the areas where species displaced one another as they shifted their ranges.
- Published
- 2013
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39. Optimization of wildlife management in a large game reserve through waterpoints manipulation: a bio-economic analysis.
- Author
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Mwakiwa E, de Boer WF, Hearne JW, Slotow R, van Langevelde F, Peel M, Grant CC, Pretorius Y, Stigter JD, Skidmore AK, Heitkönig IM, de Knegt HJ, Kohi EM, Knox N, and Prins HH
- Subjects
- Animals, Antelopes, Ecosystem, Conservation of Natural Resources, Elephants, Models, Economic, Water Supply
- Abstract
Surface water is one of the constraining resources for herbivore populations in semi-arid regions. Artificial waterpoints are constructed by wildlife managers to supplement natural water supplies, to support herbivore populations. The aim of this paper is to analyse how a landowner may realize his ecological and economic goals by manipulating waterpoints for the management of an elephant population, a water-dependent species in the presence of water-independent species. We develop a theoretical bio-economic framework to analyse the optimization of wildlife management objectives (in this case revenue generation from both consumptive and non-consumptive use and biodiversity conservation), using waterpoint construction as a control variable. The model provides a bio-economic framework for analysing optimization problems where a control has direct effects on one herbivore species but indirect effects on the other. A landowner may be interested only in maximization of profits either from elephant offtake and/or tourism revenue, ignoring the negative effects that could be brought about by elephants to biodiversity. If the landowner does not take the indirect effects of waterpoints into consideration, then the game reserve management, as the authority entrusted with the sustainable management of the game reserve, might use economic instruments such as subsidies or taxes to the landowners to enforce sound waterpoint management., (Copyright © 2012 Elsevier Ltd. All rights reserved.)
- Published
- 2013
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40. Soil biotic impact on plant species shoot chemistry and hyperspectral reflectance patterns.
- Author
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Carvalho S, Macel M, Schlerf M, Skidmore AK, and van der Putten WH
- Subjects
- Biomass, Carbon analysis, Chlorophyll analysis, Chlorophyll A, Introduced Species, Nitrogen analysis, Spectrum Analysis methods, Asteraceae growth & development, Plant Shoots chemistry, Plant Shoots growth & development, Senecio growth & development, Soil Microbiology
- Abstract
Recent studies revealed that plant-soil biotic interactions may cause changes in above-ground plant chemistry. It would be a new step in below-ground-above-ground interaction research if such above-ground chemistry changes could be efficiently detected. Here we test how hyperspectral reflectance may be used to study such plant-soil biotic interactions in a nondestructive and rapid way. The native plant species Jacobaea vulgaris and Jacobaea erucifolius, and the exotic invader Senecio inaequidens were grown in different soil biotic conditions. Biomass, chemical content and shoot reflectance between 400 and 2500 nm wavelengths were determined. The data were analysed with multivariate statistics. Exposing the plants to soil biota enhanced the content of defence compounds. The highest increase (400%) was observed for the exotic invader S. inaequidens. Chemical and spectral data enabled plant species to be classified with an accuracy > 85%. Plants grown in different soil conditions were classified with 50-60% correctness. Our data suggest that soil microorganisms can affect plant chemistry and spectral reflectance. Further studies should test the potential to study plant-soil biotic interactions in the field. Such techniques could help to monitor, among other things, where invasive exotic plant species develop biotic resistance or the development of hotspots of crop soil diseases., (© 2012 The Authors. New Phytologist © 2012 New Phytologist Trust.)
- Published
- 2012
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41. An accurate retrieval of leaf water content from mid to thermal infrared spectra using continuous wavelet analysis.
- Author
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Ullah S, Skidmore AK, Naeem M, and Schlerf M
- Subjects
- Magnoliopsida chemistry, Plant Leaves chemistry, Spectrophotometry, Infrared methods, Water analysis, Wavelet Analysis
- Abstract
Leaf water content determines plant health, vitality, photosynthetic efficiency and is an important indicator of drought assessment. The retrieval of leaf water content from the visible to shortwave infrared spectra is well known. Here for the first time, we estimated leaf water content from the mid to thermal infrared (2.5-14.0 μm) spectra, based on continuous wavelet analysis. The dataset comprised 394 spectra from nine plant species, with different water contents achieved through progressive drying. To identify the spectral feature most sensitive to the variations in leaf water content, first the Directional Hemispherical Reflectance (DHR) spectra were transformed into a wavelet power scalogram, and then linear relations were established between the wavelet power scalogram and leaf water content. The six individual wavelet features identified in the mid infrared yielded high correlations with leaf water content (R(2)=0.86 maximum, 0.83 minimum), as well as low RMSE (minimum 8.56%, maximum 9.27%). The combination of four wavelet features produced the most accurate model (R(2)=0.88, RMSE=8.00%). The models were consistent in terms of accuracy estimation for both calibration and validation datasets, indicating that leaf water content can be accurately retrieved from the mid to thermal infrared domain of the electromagnetic radiation., (Copyright © 2012 Elsevier B.V. All rights reserved.)
- Published
- 2012
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42. Corresponding mitochondrial DNA and niche divergence for crested newt candidate species.
- Author
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Wielstra B, Beukema W, Arntzen JW, Skidmore AK, Toxopeus AG, and Raes N
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- Animals, Ecosystem, Genetic Variation, Phylogeography, Principal Component Analysis, DNA, Mitochondrial genetics, Evolution, Molecular, Triturus genetics
- Abstract
Genetic divergence of mitochondrial DNA does not necessarily correspond to reproductive isolation. However, if mitochondrial DNA lineages occupy separate segments of environmental space, this supports the notion of their evolutionary independence. We explore niche differentiation among three candidate species of crested newt (characterized by distinct mitochondrial DNA lineages) and interpret the results in the light of differences observed for recognized crested newt species. We quantify niche differences among all crested newt (candidate) species and test hypotheses regarding niche evolution, employing two ordination techniques (PCA-env and ENFA). Niche equivalency is rejected: all (candidate) species are found to occupy significantly different segments of environmental space. Furthermore, niche overlap values for the three candidate species are not significantly higher than those for the recognized species. As the three candidate crested newt species are, not only in terms of mitochondrial DNA genetic divergence, but also ecologically speaking, as diverged as the recognized crested newt species, our findings are in line with the hypothesis that they represent cryptic species. We address potential pitfalls of our methodology.
- Published
- 2012
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43. Using a genetic algorithm as an optimal band selector in the mid and thermal infrared (2.5-14 μm) to discriminate vegetation species.
- Author
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Ullah S, Groen TA, Schlerf M, Skidmore AK, Nieuwenhuis W, and Vaiphasa C
- Abstract
Genetic variation between various plant species determines differences in their physio-chemical makeup and ultimately in their hyperspectral emissivity signatures. The hyperspectral emissivity signatures, on the one hand, account for the subtle physio-chemical changes in the vegetation, but on the other hand, highlight the problem of high dimensionality. The aim of this paper is to investigate the performance of genetic algorithms coupled with the spectral angle mapper (SAM) to identify a meaningful subset of wavebands sensitive enough to discriminate thirteen broadleaved vegetation species from the laboratory measured hyperspectral emissivities. The performance was evaluated using an overall classification accuracy and Jeffries Matusita distance. For the multiple plant species, the targeted bands based on genetic algorithms resulted in a high overall classification accuracy (90%). Concentrating on the pairwise comparison results, the selected wavebands based on genetic algorithms resulted in higher Jeffries Matusita (J-M) distances than randomly selected wavebands did. This study concludes that targeted wavebands from leaf emissivity spectra are able to discriminate vegetation species.
- Published
- 2012
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44. Soil nutrient status determines how elephant utilize trees and shape environments.
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Pretorius Y, de Boer FW, van der Waal C, de Knegt HJ, Grant RC, Knox NM, Kohi EM, Mwakiwa E, Page BR, Peel MJ, Skidmore AK, Slotow R, van Wieren SE, and Prins HH
- Subjects
- Animals, Ecosystem, Nitrogen metabolism, Phosphorus metabolism, South Africa, Trees metabolism, Elephants physiology, Fabaceae metabolism, Food Preferences, Plant Leaves metabolism, Soil analysis
- Abstract
1. Elucidation of the mechanism determining the spatial scale of patch selection by herbivores has been complicated by the way in which resource availability at a specific scale is measured and by vigilance behaviour of the herbivores themselves. To reduce these complications, we studied patch selection by an animal with negligible predation risk, the African elephant. 2. We introduce the concept of nutrient load as the product of patch size, number of patches and local patch nutrient concentration. Nutrient load provides a novel spatially explicit expression of the total available nutrients a herbivore can select from. 3. We hypothesized that elephant would select nutrient-rich patches, based on the nutrient load per 2500 m(2) down to the individual plant scale, and that this selection will depend on the nitrogen and phosphorous contents of plants. 4. We predicted that elephant would cause more adverse impact to trees of lower value to them in order to reach plant parts with higher nutrient concentrations such as bark and root. However, elephant should maintain nutrient-rich trees by inducing coppicing of trees through re-utilization of leaves. 5. Elephant patch selection was measured in a homogenous tree species stand by manipulating the spatial distribution of soil nutrients in a large field experiment using NPK fertilizer. 6. Elephant were able to select nutrient-rich patches and utilized Colophospermum mopane trees inside these patches more than outside, at scales ranging from 2500 down to 100 m(2) . 7. Although both nitrogen and phosphorus contents of leaves from C. mopane trees were higher in fertilized and selected patches, patch choice correlated most strongly with nitrogen content. As predicted, stripping of leaves occurred more in nutrient-rich patches, while adverse impact such as uprooting of trees occurred more in nutrient-poor areas. 8. Our results emphasize the necessity of including scale-dependent selectivity in foraging studies and how elephant foraging behaviour can be used as indicators of change in the availability of nutrients., (© 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.)
- Published
- 2011
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45. The spatial scaling of habitat selection by African elephants.
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de Knegt HJ, van Langevelde F, Skidmore AK, Delsink A, Slotow R, Henley S, Bucini G, de Boer WF, Coughenour MB, Grant CC, Heitkönig IM, Henley M, Knox NM, Kohi EM, Mwakiwa E, Page BR, Peel M, Pretorius Y, van Wieren SE, and Prins HH
- Subjects
- Animals, Demography, Female, Male, Models, Biological, South Africa, Ecosystem, Elephants physiology
- Abstract
1. Understanding and accurately predicting the spatial patterns of habitat use by organisms is important for ecological research, biodiversity conservation and ecosystem management. However, this understanding is complicated by the effects of spatial scale, because the scale of analysis affects the quantification of species-environment relationships. 2. We therefore assessed the influence of environmental context (i.e. the characteristics of the landscape surrounding a site), varied over a large range of scales (i.e. ambit radii around focal sites), on the analysis and prediction of habitat selection by African elephants in Kruger National Park, South Africa. 3. We focused on the spatial scaling of the elephants' response to their main resources, forage and water, and found that the quantification of habitat selection strongly depended on the scales at which environmental context was considered. Moreover, the inclusion of environmental context at characteristic scales (i.e. those at which habitat selectivity was maximized) increased the predictive capacity of habitat suitability models. 4. The elephants responded to their environment in a scale-dependent and perhaps hierarchical manner, with forage characteristics driving habitat selection at coarse spatial scales, and surface water at fine spatial scales. 5. Furthermore, the elephants exhibited sexual habitat segregation, mainly in relation to vegetation characteristics. Male elephants preferred areas with high tree cover and low herbaceous biomass, whereas this pattern was reversed for female elephants. 6. We show that the spatial distribution of elephants can be better understood and predicted when scale-dependent species-environment relationships are explicitly considered. This demonstrates the importance of considering the influence of spatial scale on the analysis of spatial patterning in ecological phenomena., (© 2010 The Authors. Journal compilation © 2010 British Ecological Society.)
- Published
- 2011
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46. Soil erosion and sediment yield and their relationships with vegetation cover in upper stream of the Yellow River.
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Ouyang W, Hao F, Skidmore AK, and Toxopeus AG
- Subjects
- China, Environmental Monitoring, Geologic Sediments analysis, Seasons, Geologic Sediments chemistry, Geological Phenomena, Plant Development, Rivers chemistry, Soil chemistry, Water Pollutants analysis
- Abstract
Soil erosion is a significant concern when considering regional environmental protection, especially in the Yellow River Basin in China. This study evaluated the temporal-spatial interaction of land cover status with soil erosion characteristics in the Longliu Catchment of China, using the Soil and Water Assessment Tool (SWAT) model. SWAT is a physical hydrological model which uses the RUSLE equation as a sediment algorithm. Considering the spatial and temporal scale of the relationship between soil erosion and sediment yield, simulations were undertaken at monthly and annual temporal scales and basin and sub-basin spatial scales. The corresponding temporal and spatial Normalized Difference Vegetation Index (NDVI) information was summarized from MODIS data, which can integrate regional land cover and climatic features. The SWAT simulation revealed that the annual soil erosion and sediment yield showed similar spatial distribution patterns, but the monthly variation fluctuated significantly. The monthly basin soil erosion varied from almost no erosion load to 3.92 t/ha and the maximum monthly sediment yield was 47,540 tones. The inter-annual simulation focused on the spatial difference and relationship with the corresponding vegetation NDVI value for every sub-basin. It is concluded that, for this continental monsoon climate basin, the higher NDVI vegetation zones prevented sediment transport, but at the same time they also contributed considerable soil erosion. The monthly basin soil erosion and sediment yield both correlated with NDVI, and the determination coefficients of their exponential correlation model were 0.446 and 0.426, respectively. The relationships between soil erosion and sediment yield with vegetation NDVI indicated that the vegetation status has a significant impact on sediment formation and transport. The findings can be used to develop soil erosion conservation programs for the study area., (Copyright © 2010 Elsevier B.V. All rights reserved.)
- Published
- 2010
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47. Spatial autocorrelation and the scaling of species-environment relationships.
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De Knegt HJ, van Langevelde F, Coughenour MB, Skidmore AK, de Boer WF, Heitkönig IM, Knox NM, Slotow R, van der Waal C, and Prins HH
- Subjects
- Animals, Population Dynamics, Rain, Trees, Computer Simulation, Ecosystem, Models, Biological
- Abstract
Issues of residual spatial autocorrelation (RSA) and spatial scale are critical to the study of species-environment relationships, because RSA invalidates many statistical procedures, while the scale of analysis affects the quantification of these relationships. Although these issues independently are widely covered in the literature, only sparse attention is given to their integration. This paper focuses on the interplay between RSA and the spatial scaling of species-environment relationships. Using a hypothetical species in an artificial landscape, we show that a mismatch between the scale of analysis and the scale of a species' response to its environment leads to a decrease in the portion of variation explained by environmental predictors. Moreover, it results in RSA and biased regression coefficients. This bias stems from error-predictor dependencies due to the scale mismatch, the magnitude of which depends on the interaction between the scale of landscape heterogeneity and the scale of a species' response to this heterogeneity. We show that explicitly considering scale effects on RSA can reveal the characteristic scale of a species' response to its environment. This is important, because the estimation of species-environment relationships using spatial regression methods proves to be erroneous in case of a scale mismatch, leading to spurious conclusions when scaling issues are not explicitly considered. The findings presented here highlight the importance of examining the appropriateness of the spatial scales used in analyses, since scale mismatches affect the rigor of statistical analyses and thereby the ability to understand the processes underlying spatial patterning in ecological phenomena.
- Published
- 2010
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48. Soil erosion dynamics response to landscape pattern.
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Ouyang W, Skidmore AK, Hao F, and Wang T
- Subjects
- Environmental Monitoring, Geography, Kinetics, Water Supply analysis, Water Supply statistics & numerical data, Conservation of Natural Resources, Soil analysis, Water Pollutants analysis
- Abstract
Simulating soil erosion variation with a temporal land use database reveals long-term fluctuations in landscape patterns, as well as priority needs for soil erosion conservation. The application of a multi-year land use database in support of a Soil Water Assessment Tool (SWAT) led to an accurate assessment, from 1977 to 2006, of erosion in the upper watershed of the Yellow River. At same time, the impacts of land use and landscape service features on soil erosion load were assessed. A series of supervised land use classifications of Landsat images characterized variations in land use and landscape patterns over three decades. The SWAT database was constructed with soil properties, climate and elevation data. Using water flow and sand density data as parameters, regional soil erosion load was simulated. A numerical statistical model was used to relate soil erosion to land use and landscape. The results indicated that decadal decrease of grassland areas did not pose a significant threat to soil erosion, while the continual increase of bare land, water area and farmland increased soil erosion. Regional landscape variation also had a strong relationship with erosion. Patch level landscape analyses demonstrated that larger water area led to more soil erosion. The patch correlation indicated that contagious grassland patches reduced soil erosion yield. The increased grassland patches led to more patch edges, in turn increasing the sediment transportation from the patch edges. The findings increase understanding of the temporal variation in soil erosion processes, which is the basis for preventing local pollution.
- Published
- 2010
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49. Spatio-temporal dynamics of global H5N1 outbreaks match bird migration patterns.
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Si Y, Skidmore AK, Wang T, de Boer WF, Debba P, Toxopeus AG, Li L, and Prins HH
- Subjects
- Animals, Birds, Geography, Humans, Influenza in Birds virology, Population Surveillance, Space-Time Clustering, Wetlands, Animal Migration, Disease Outbreaks, Influenza A Virus, H5N1 Subtype pathogenicity, Influenza in Birds epidemiology, Influenza, Human epidemiology
- Abstract
The global spread of highly pathogenic avian influenza H5N1 in poultry, wild birds and humans, poses a significant pandemic threat and a serious public health risk. An efficient surveillance and disease control system relies on the understanding of the dispersion patterns and spreading mechanisms of the virus. A space-time cluster analysis of H5N1 outbreaks was used to identify spatio-temporal patterns at a global scale and over an extended period of time. Potential mechanisms explaining the spread of the H5N1 virus, and the role of wild birds, were analyzed. Between December 2003 and December 2006, three global epidemic phases of H5N1 influenza were identified. These H5N1 outbreaks showed a clear seasonal pattern, with a high density of outbreaks in winter and early spring (i.e., October to March). In phase I and II only the East Asia Australian flyway was affected. During phase III, the H5N1 viruses started to appear in four other flyways: the Central Asian flyway, the Black Sea Mediterranean flyway, the East Atlantic flyway and the East Africa West Asian flyway. Six disease cluster patterns along these flyways were found to be associated with the seasonal migration of wild birds. The spread of the H5N1 virus, as demonstrated by the space-time clusters, was associated with the patterns of migration of wild birds. Wild birds may therefore play an important role in the spread of H5N1 over long distances. Disease clusters were also detected at sites where wild birds are known to overwinter and at times when migratory birds were present. This leads to the suggestion that wild birds may also be involved in spreading the H5N1 virus over short distances.
- Published
- 2009
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50. Concurrent monitoring of vessels and water turbidity enhances the strength of evidence in remotely sensed dredging impact assessment.
- Author
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Wu G, de Leeuw J, Skidmore AK, Prins HH, and Liu Y
- Subjects
- China, Environmental Monitoring, Fresh Water, Nephelometry and Turbidimetry, Satellite Communications, Engineering, Environment, Ships, Water Pollution
- Abstract
Remotely sensed assessment of dredging impacts on water turbidity is straightforward when turbidity plumes show up in clear water. However, it is more complicated in turbid waters as the spatial or temporal changes in turbidity might be of natural origin. The plausibility of attributing turbidity patterns to dredging activities would be greatly enhanced when demonstrating association between dredging infrastructure and water turbidity. This study investigated the possibility to strengthen the inference of dredging impact while simultaneously monitoring vessels and water turbidity in the northern Poyang Lake, China, where dredging was first introduced in 2001 and rapidly extended onwards. Time-series of Landsat TM and MODIS images of 2000-2005 were used to estimate the distribution and number of vessels as well as water turbidity. MODIS images revealed a significant increase in water turbidity from 2001 onwards. Landsat TM image analysis indicated a simultaneous increase in the number of vessels. Regression analysis further showed a highly significant positive relationship (R2=0.92) between water turbidity and vessel number. Visual interpretation of ship locations led to the conclusion that clear upstream waters developed turbidity plumes while passing the first cluster of vessels. We concluded that dredging caused the increase in water turbidity, and simultaneously monitoring the water turbidity and vessels enhanced the strength of evidence in remotely sensed dredging impact assessment.
- Published
- 2007
- Full Text
- View/download PDF
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