The Experts below are selected from a list of 73863 Experts worldwide ranked by ideXlab platform
Wei Zhang - One of the best experts on this subject based on the ideXlab platform.
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Small-scale Vegetation Dynamics in semi-arid steppe in Inner Mongolia
Journal of Arid Environments, 1996Co-Authors: Wei Zhang, Christina SkarpeAbstract:Abstract Small-scale Vegetation Dynamics were followed for ecotones and in uniform stands in Artemisia -dominated steppe Vegetation under grazing and when recovering from heavy grazing. Species composition was followed annually for 5 years in 1 m 2 and 0·25 m 2 plots for (1) presence–absence; (2) density; and (3) biomass. More rapid Vegetation Dynamics, in terms of change of type of Vegetation and distance moved in DCA species space between sampling occasions, were observed in smaller plots and in early seral stages, where species were few and alpha diversity low. Only the plots recently protected from grazing showed a directional Vegetation change; those protected for more than 3 years and those under continued grazing showed, at this scale, non-directional Dynamics.
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Vegetation Dynamics in Relation to Livestock Grazing in a Semi-Arid Steppe in Inner Mongolia
1995Co-Authors: Wei ZhangAbstract:Vegetation Dynamics in relation to livestock grazing in a semi-arid steppe in inner Mongolia
Ronen Kadmon - One of the best experts on this subject based on the ideXlab platform.
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SPATIOTEMPORAL PREDICTIVE MODELS OF MEDITERRANEAN Vegetation Dynamics
Ecological Applications, 2001Co-Authors: Yohay Carmel, Ronen Kadmon, Ronit NirelAbstract:Empirical modeling of Vegetation Dynamics can be used for predictive pur- poses. The goal of the present study is to construct and evaluate possible approaches for empirical modeling of Vegetation Dynamics, and to investigate their potential use in planning and management. An empirical model of mediterranean Vegetation Dynamics was constructed using a case study of Vegetation change in an area in the Galilee mountains, northern Israel, between 1964 and 1992. Present Vegetation in any location was modeled as a function of past Vegetation and environmental factors (e.g., topography and various disturbances); future Vegetation was then modeled as a function of current Vegetation and effects of environmental factors. In order to assess model performance, we compared the actual Vegetation map with maps representing model realizations for the study area and for an external validation area. Three types of measures were used to compare the predicted and actual Vegetation maps: overall Vegetation composition, pattern indices, and cell-by-cell match. We compared the performance of logistic vs. linear models and of stochastic vs. deterministic realizations of a logistic model. Our results indicate that landscape-scale Vegetation Dynamics can be fairly well modeled using a few biologically important variables. The logistic and linear models had similar performance, in spite of the reduced information on which the logistic models were based. The use of only a 4% sample of the database resulted in a negligible reduction in model performance. Model performance was reduced, but was still fair, when applied to an external area. The merits and limitations of this modeling approach are discussed in comparison with other approaches for modeling Vegetation Dynamics.
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Studying long-term Vegetation Dynamics using digital processing of historical aerial photographs
Remote Sensing of Environment, 1999Co-Authors: Ronen Kadmon, Ruthie Harari-kremerAbstract:Plant ecologists have long recognized the importance of aerial photographs as a data source for studies of Vegetation Dynamics. Recent advances in computer-aided technology (digital photogrammetry, computerized image processing, and geographical information systems) have opened new possibilities for the extraction of data on Vegetation changes from aerial photographs. In this study we describe a computer-based approach for studying landscape-scale, long-term Vegetation Dynamics, using historical aerial photographs as a major data source. The method we employ consists of four main steps: 1) image scanning and preprocessing (rectification, georeferencing, spectral corrections and mosaicking), 2) image classification and construction of Vegetation maps, 3) field validation, and 4) statistical analysis of Vegetation changes. We applied our approach by analyzing changes in tree cover over a period of 32 years in a mountainous landscape dominated by Mediterranean maquis in northern Israel and discuss the main limitations and potential error sources of each stage of our analysis. We conclude that digital processing of historical aerial photographs may serve as a powerful tool for the detection, quantification, and analysis of landscape-scale patterns of Vegetation Dynamics. This conclusion is important because aerial photographs provide the largest source of information available today for research of long-term Vegetation Dynamics, and are the only source of information on Vegetation Dynamics that combines high spatial resolution, large spatial extent, and long-term coverage.
Qiuwen Chen - One of the best experts on this subject based on the ideXlab platform.
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ACRI - Unstructured Cellular Automata and the Application to Model River Riparian Vegetation Dynamics
Lecture Notes in Computer Science, 1Co-Authors: Qiuwen ChenAbstract:Cellular automata (CA) have proved to be a robust approach to spatially-explicit modeling of ecosystems. Conventionally the CA models applied a structured square grid. However, due to the anisotropic properties of environmental conditions, the capability of CA method was not fully explored when using the regular squared lattice. This research investigated the unstructured cellular automata (UCA) by implementing a irregular triangular grid and used it to develop a Vegetation Dynamics model. The model was then coupled with a two-dimensional hydrodynamic model to simulate the riparian Vegetation Dynamics due to flow modifications by the reservoirs operations. The integrated model was applied to a compound channel of the Lijiang River in the Southwest China, which has been affected by the flow regulations for navigation purpose. Through the simulations, the previous evolutions of the riparian Vegetations were recaptured and their future developments under the new flow regulation scheme were predicted. In particular, the potentials of UCA in ecosystem modeling were illustrated in the research.
Benjamin W. Heumann - One of the best experts on this subject based on the ideXlab platform.
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Disentangling the effects of climate and people on Sahel Vegetation Dynamics
Biogeosciences, 2009Co-Authors: Jonathan Seaquist, Thomas Hickler, Lars Eklundh, Jonas Ardö, Benjamin W. HeumannAbstract:Abstract. The Sahel belt of Africa has been the focus of intensive scientific research since the 1960s, spurred on by the chronic vulnerability of its population to recurring drought and the threat of long-term land degradation. But satellite sensors have recently shown that much of the region has experienced significant increases in photosynthetic activity since the early 1980s, thus re-energizing long-standing debates about the role that people play in shaping land surface status, and thus climate at regional scales. In this paper, we test the hypothesis that people have had a measurable impact on Vegetation Dynamics in the Sahel for the period 1982–2002. We compare potential natural Vegetation Dynamics predicted by a process-based ecosystem model with satellite-derived greenness observations, and map the agreement between the two across a geographic grid at a spatial resolution of 0.5°. As aggregated data-model agreement is very good, any local differences between the two could be due to human impact. We then relate this agreement metric to state-of-the-art data sets on demographics, pasture, and cropping. Our findings suggest that demographic and agricultural pressures in the Sahel are unable to account for differences between simulated and observed Vegetation Dynamics, even for the most densely populated areas. But we do identify a weak, positive correlation between data-model agreement and pasture intensity at the Sahel-wide level. This indicates that herding or grazing does not appreciably affect Vegetation Dynamics in the region. Either people have not had a significant impact on Vegetation Dynamics in the Sahel or the identification of a human "footprint" is precluded by inconsistent or subtle Vegetation response to complex socio-environmental interactions, and/or limitations in the data used for this study. We do not exclude the possibility of a greater human influence on Vegetation Dynamics over the coming decades with changing land use.
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Disentangling the effects of climate and people on Sahel Vegetation Dynamics
2008Co-Authors: Jonathan Seaquist, Thomas Hickler, Lars Eklundh, Jonas Ardö, Benjamin W. HeumannAbstract:Abstract. The Sahel belt of Africa has been the focus of intensive scientific research since the 1960s, spurred on by the chronic vulnerability of its population to recurring drought and the threat of long-term land degradation. But satellite sensors have recently shown that much of the region has experienced significant increases in photosynthetic activity since the early 1980s, thus re-energizing long-standing debates about the role that people play in shaping land surface status, and thus climate at regional scales. In this paper, we test the hypothesis that people have had a measurable impact on Vegetation Dynamics in the Sahel for the period 1982–2002. We compare potential natural Vegetation Dynamics predicted by a process-based ecosystem model with satellite-derived greenness observations, and map the agreement between the two across a geographic grid at a spatial resolution of 0.5°. As aggregated data-model agreement is very good, any local differences between the two could be due to human impact. We then relate this agreement metric to state-of-the-art data sets on demographics, pasture, and cropping. Our findings suggest that demographic and agricultural pressures in the Sahel are unable to account for differences between simulated and observed Vegetation Dynamics, even for the most densely populated areas. But we do identify a weak, positive correlation between data-model agreement and pasture intensity at the Sahel-wide level. This indicates that herding or grazing does not appreciably affect Vegetation Dynamics in the region. Either people have not had a significant impact on Vegetation Dynamics in the Sahel or the identification of a human "footprint" is precluded by inconsistent or subtle Vegetation response to complex socio-environmental interactions, and/or limitations in the data used for this study.
Ruthie Harari-kremer - One of the best experts on this subject based on the ideXlab platform.
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Studying long-term Vegetation Dynamics using digital processing of historical aerial photographs
Remote Sensing of Environment, 1999Co-Authors: Ronen Kadmon, Ruthie Harari-kremerAbstract:Plant ecologists have long recognized the importance of aerial photographs as a data source for studies of Vegetation Dynamics. Recent advances in computer-aided technology (digital photogrammetry, computerized image processing, and geographical information systems) have opened new possibilities for the extraction of data on Vegetation changes from aerial photographs. In this study we describe a computer-based approach for studying landscape-scale, long-term Vegetation Dynamics, using historical aerial photographs as a major data source. The method we employ consists of four main steps: 1) image scanning and preprocessing (rectification, georeferencing, spectral corrections and mosaicking), 2) image classification and construction of Vegetation maps, 3) field validation, and 4) statistical analysis of Vegetation changes. We applied our approach by analyzing changes in tree cover over a period of 32 years in a mountainous landscape dominated by Mediterranean maquis in northern Israel and discuss the main limitations and potential error sources of each stage of our analysis. We conclude that digital processing of historical aerial photographs may serve as a powerful tool for the detection, quantification, and analysis of landscape-scale patterns of Vegetation Dynamics. This conclusion is important because aerial photographs provide the largest source of information available today for research of long-term Vegetation Dynamics, and are the only source of information on Vegetation Dynamics that combines high spatial resolution, large spatial extent, and long-term coverage.
