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  • 1
    Language: English
    In: Ecological Modelling, 2011, Vol.222(3), pp.475-484
    Description: State-and-transition models (STMs) can represent many different types of landscape change, from simple gradient-driven transitions to complex, (pseudo-) random patterns. While previous applications of STMs have focused on individual states and transitions, this study addresses broader-scale modes of spatial change based on the entire network of states and transitions. STMs are treated as mathematical graphs, and several metrics from algebraic graph theory are applied—spectral radius, algebraic connectivity, and the -metric. These indicate, respectively, the amplification of environmental change by state transitions, the relative rate of propagation of state changes through the landscape, and the degree of system structural constraints on the spatial propagation of state transitions. The analysis is illustrated by application to the Gualalupe/San Antonio River delta, Texas, with soil types as representations of system states. Concepts of change in deltaic environments are typically based on successional patterns in response to forcings such as sea level change or river inflows. However, results indicate more complex modes of change associated with amplification of changes in system states, relatively rapid spatial propagation of state transitions, and some structural constraints within the system. The implications are that complex, spatially variable state transitions are likely, constrained by local (within-delta) environmental gradients and initial conditions. As in most applications, the STM used in this study is a representation of observed state transitions. While the usual predictive application of STMs is identification of local state changes associated with, e.g., management strategies, the methods presented here show how STMs can be used at a broader scale to identify landscape scale modes of spatial change.
    Keywords: State-and-Transition Models ; Spectral Radius ; Algebraic Connectivity ; S-Metric ; Spatial Change ; Landscape Change ; Environmental Sciences ; Ecology
    ISSN: 0304-3800
    E-ISSN: 1872-7026
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  • 2
    Language: English
    In: Ecological Modelling, 24 February 2015, Vol.298, pp.16-23
    Description: Chronosequences are a fundamental tool for studying and representing change in Earth surface systems. Increasingly, chronosequences are understood to be much more complex than a simple monotonic progression from a starting point to a stable end-state. The concept of path stability is introduced here as a measure of chronosequence robustness; i.e., the degree to which developmental trajectories are sensitive to disturbances or change. Path stability is assessed on the basis of the largest Lyapunov exponent ( ) of an interaction matrix consisting of positive, negative, or zero entries based on whether existence of a given system state or stage promotes or facilitates (positive), prevents or inhibits (negative), or has no significant effect on transitions to another state. Analysis of several generic chronosequence structures represented as signed, directed, unweighted graphs indicates five general cases: Path-stable reversible progressions ( 〈 0); neutrally path-stable irreversible progressions ( = 0); path unstable with very low divergence (0 〈 〈 1); path unstable with low divergence ( = 1); and complex multiple pathways ( 〉 1). Path stability is probably relatively rare in chronosequences due to the directionality inherent in most of them. A complex soil chronosequence on the lower coastal plain of North Carolina was analyzed as described above, yielding = 0.843, indicating very low divergence. This outcome is consistent with pedological interpretations, and derives largely from the presence of self-limiting early stages, and a few highly developed states that inhibit retrogression back to many of the earlier stages. This kind of structure is likely to be common in pedological and hydrological sequences, but this suggestion requires further testing.
    Keywords: Robustness ; Path Stability ; Chronosequence ; Coevolution ; Earth Surface Systems ; Environmental Sciences ; Ecology
    ISSN: 0304-3800
    E-ISSN: 1872-7026
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  • 3
    Language: English
    In: Ecological Modelling, Feb 24, Vol.298, p.16(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ecolmodel.2013.12.018 Byline: Jonathan D. Phillips Abstract: * Robustness (path stability) of chronosequences was analyzed. * Potential divergence of evolutionary paths following environmental change. * Interaction matrix reflects facilitation or inhibition of state changes. * Applied to soil chronosequence, revealing very low divergence. Author Affiliation: Tobacco Road Research Team, Department of Geography, University of Kentucky, Lexington, KY 40506-0027, USA
    ISSN: 0304-3800
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: Journal of Environmental Management, 2011, Vol.92(2), pp.284-289
    Description: Rivers crossing coastal plains are often inefficient conveyors of sediment, so that changes in upstream sediment dynamics are not evident at the river mouth. Extensive accommodation space and low stream power often result in extensive alluvial storage upstream of estuaries and correspondingly low sediment loads at the river mouth. However, gaging stations with sediment records are typically well upstream of the coast, and thus tend to overestimate sediment yields by under-representing the lower coastal plain and because there is often a net loss of sediment in lower coastal plain reaches. Studies of alluvial sediment storage have generally focused on accommodation space, but, using examples from Texas, we show that low transport capacity controlled largely by slope is a crucial factor.
    Keywords: Sediment Flux ; Low Energy Rivers ; Texas ; Dams ; Alluvial Storage ; Environmental Sciences ; Economics
    ISSN: 0301-4797
    E-ISSN: 1095-8630
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  • 5
    Language: English
    In: Ecological Modelling, Sept 10, 2013, Vol.265, p.64(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ecolmodel.2013.06.002 Byline: Daehyun Kim, Jonathan D. Phillips Abstract: acents Modes of vegetation dynamics were analyzed in a Danish salt marsh. acents Graph theory was applied to state-and-transition models of succession. acents Observed succession showed strong amplification and synchronization. acents This implies possible abrupt system reorganization. acents The approach helps to identify holistic properties of system dynamics. Author Affiliation: Tobacco Road Research Team, Department of Geography, University of Kentucky, Lexington, KY 40506-0027, United States Article History: Received 22 February 2013; Revised 22 May 2013; Accepted 2 June 2013
    Keywords: Vegetation Dynamics ; Salt Marshes
    ISSN: 0304-3800
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Climatic Change, 2010, Vol.103(3), pp.571-595
    Description: Efforts to predict responses to climate change and to interpret modern or paleoclimate indicators are influenced by several levels of potential amplifiers, which increase or exaggerate climate impacts, and/or filters, which reduce or mute impacts. With respect to geomorphic responses and indicators, climate forcings are partly mediated by ecological, hydrological, and other processes which may amplify or filter impacts on surface processes and landforms. Then, geomorphic responses themselves may be threshold-dominated or dynamically unstable, producing disproportionately large and long-lived responses to climate changes or disturbances. Or, responses may be dynamically stable, whereby resistance or resilience of geomorphic systems minimizes the effects of changes. Thus a given geomorphic response to climate could represent (at least) two levels of amplification and/or filtering. An example is given for three fluvial systems in Kentucky, U.S.A, the Kentucky, Green, and Big South Fork Rivers. Climate impacts in the early Quaternary were amplified by glacially-driven reorganization of the ancestral Ohio River system to the North, and by dynamical instability in the down-cutting response of rivers incising plateau surfaces. Effects of more recent climate changes, however, have been filtered to varying extents. Using alluvial terraces as an example, the study rivers show distinctly different responses to climate forcings. The lower Green River has extensive, well-developed terraces recording several episodes of aggradation and downcutting, while the Big South Fork River has no alluvial terraces. The Kentucky River is intermediate, with limited preservation of relatively recent terraces. The differences can be explained in terms of differences among the rivers in (1) filtering effects of constraints on fluvial responses imposed by strongly incised, steep-walled bedrock controlled valleys; and (2) amplifier effects of periodic damming of lower river reaches by glaciofluvial outwash.
    Keywords: Climate Change -- Research ; Geomorphology -- Research ; Rivers -- Environmental Aspects;
    ISSN: 0165-0009
    E-ISSN: 1573-1480
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  • 7
    Language: English
    In: Applied Cognitive Psychology, September 2011, Vol.25(5), pp.768-774
    Description: Field implementation of double‐blind sequential lineups has prompted a question about the impact on eyewitness decisions of an explicit not‐sure response option. In this laboratory study, a video crime was viewed by 378 participants who then attempted to identify the culprit from a six‐person sequential or simultaneous‐format lineup that either included or did not include the culprit. Witnesses were provided either dichotomous forced‐choice (FC) response categories (/) or a not‐sure option as one of three response categories (//). The not‐sure option (NSO) significantly decreased witness choosing compared to the FC condition but only for sequential lineups. Both correct identifications and false alarms decreased. Diagnosticity was greatest for a sequential lineup with a NSO. The results suggest a criterion decision shift for witnesses who view a sequential lineup with a not‐sure response option. Copyright © 2010 John Wiley & Sons, Ltd.
    Keywords: Lineups ; Eyewitnesses ; Identification ; Laboratories ; Attitudes ; Alarms ; Article;
    ISSN: 0888-4080
    E-ISSN: 1099-0720
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  • 8
    Language: English
    In: Ecological modelling, 2013, Vol.265, pp.64-73
    Description: The recent literature suggests that the network structure of ecological states within a system can determine whether the system's response to environmental changes is reinforced by positive feedback mechanisms (amplification); rapidly propagated throughout the entire network of states (synchronization); or structurally constrained. The purpose of this research was to predict these various modes of system dynamics in the context of vegetation change represented as state-and-transition models (STMs) at a salt marsh of the Danish Wadden Sea. In the STM framework, several different plant communities identified by a classification approach were regarded as multiple alternative “states,” with “transitions” defined by observed transformations among the communities over time. Treating these STMs as mathematical graphs, three metrics from algebraic graph theory—spectral radius, algebraic connectivity, and S-metric—were calculated to characterize the degree of amplification, synchronization, and structural constraint, respectively. Results demonstrated that observed vegetation dynamics underwent stronger amplification and synchronization, and weaker constraint than hypothesized benchmark patterns such as linear sequential, cyclic, convergent, and divergent dynamics. These findings indicate that, as marsh development proceeds through vegetation processes, the connectivity among plant communities becomes enhanced, which corresponds to a higher possibility for abrupt and complex system reorganization in response to environmental changes (e.g., gradual sea-level variations and storm surges). In this way, the coupled graph theory and STM approach contributes to identifying holistic properties of an ecological system that are otherwise not evident from the conventional theories (e.g., the continuum concept) and methodologies (e.g., gradient analysis). ; p. 64-73.
    Keywords: Models ; Salt Marshes ; Sea Level ; Plant Communities ; Prediction ; Storms ; Vegetation
    ISSN: 0304-3800
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 9
    Language: English
    In: Ecological Modelling, 10 September 2013, Vol.265, pp.64-73
    Description: The recent literature suggests that the network structure of ecological states within a system can determine whether the system's response to environmental changes is reinforced by positive feedback mechanisms (amplification); rapidly propagated throughout the entire network of states (synchronization); or structurally constrained. The purpose of this research was to predict these various modes of system dynamics in the context of vegetation change represented as state-and-transition models (STMs) at a salt marsh of the Danish Wadden Sea. In the STM framework, several different plant communities identified by a classification approach were regarded as multiple alternative “states,” with “transitions” defined by observed transformations among the communities over time. Treating these STMs as mathematical graphs, three metrics from algebraic graph theory— , , and —were calculated to characterize the degree of amplification, synchronization, and structural constraint, respectively. Results demonstrated that observed vegetation dynamics underwent stronger amplification and synchronization, and weaker constraint than hypothesized benchmark patterns such as linear sequential, cyclic, convergent, and divergent dynamics. These findings indicate that, as marsh development proceeds through vegetation processes, the connectivity among plant communities becomes enhanced, which corresponds to a higher possibility for abrupt and complex system reorganization in response to environmental changes (e.g., gradual sea-level variations and storm surges). In this way, the coupled graph theory and STM approach contributes to identifying holistic properties of an ecological system that are otherwise not evident from the conventional theories (e.g., the continuum concept) and methodologies (e.g., gradient analysis).
    Keywords: Spectral Radius ; Algebraic Connectivity ; S-Metric ; Amplification ; Synchronization ; Structural Constraint ; Environmental Sciences ; Ecology
    ISSN: 0304-3800
    E-ISSN: 1872-7026
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  • 10
    Language: English
    In: The Journal of Geology, 01 January 2013, Vol.121(1), pp.000-000
    Description: Abstract Earth surface systems (ESS) are characterized by various degrees of historical contingency, which complicates efforts to relate observed features and phenomena to environmental controls. This article provides a conceptual framework for understanding and assessing historical contingency in ESS that is based on algebraic graph theory. ESS are conceptualized as consisting of components (e.g., climate, topography, and lithology) observed or inferred at time periods. Each component at each time period represents a node of a network or graph, and interactions among components constitute the links or edges. Four indexes are applied: the S -metric, which indicates the extent to which observations of part of the network (e.g., topographic changes between two time periods) are likely to represent the dynamics of the network as a whole; spectral radius, which measures coherence and potential amplification of changes or disturbances; Laplacian spectral radius, an index of the relationship between network stability and time steps and an indication of path dependence; and algebraic connectivity, which measures the inferential synchronizability. For each of these, an index on a 0–1 scale is developed, which represents high and minimum levels of historical contingency for a given n, q. These are applied to several archetypal graph structures that represent various forms of historical contingency in the geosciences and to two specific case studies involving Quaternary evolution of fluvial systems in Texas and Kentucky.
    Keywords: Geology ; Zoology;
    ISSN: 00221376
    E-ISSN: 15375269
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