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  • 1
    In: Earth Surface Processes and Landforms, January 2014, Vol.39(1), pp.71-79
    Description: Landform and landscape evolution may be convergent, whereby initial differences and irregularities are (on average) reduced and smoothed, or divergent, with increasing variation and irregularity. Convergent and divergent evolution are directly related to dynamical (in)stability. Unstable interactions among geomorphic system components tend to dominate in earlier stages of development, while stable limits often become dominant in later stages. This results in mode switching, from unstable, divergent to stable, convergent development. Divergent‐to‐convergent mode switches emerge from a common structure in many geomorphic systems: mutually reinforcing or competitive interrelationships among system components, and negative self‐effects limiting individual components. When the interactions between components are dominant, divergent evolution occurs. As threshold limits to divergent development are approached, self‐limiting effects become more important, triggering a switch to convergence. The mode shift is an emergent phenomenon, arising from basic principles of threshold modulation and gradient selection. As an example, the relationships among flow concentration, erosive force, and channel incision in fluvial systems are examined in the context of mode switching and thresholds. The commonly observed divergence in channel growth and fluvial dissection and network development, eventually transitioning to a stable, convergent configuration, is an emergent outcome of gradient selection and threshold modification, and does not imply any goal functions of balancing mass fluxes or limiting change. Copyright © 2013 John Wiley & Sons, Ltd.
    Keywords: Thresholds ; Mode Switching ; Divergent Evolution ; Convergent Evolution ; Emergence ; Geomorphic Systems
    ISSN: 0197-9337
    E-ISSN: 1096-9837
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  • 2
    Language: English
    In: Progress in Physical Geography, August 2016, Vol.40(4), pp.503-526
    Description: While karst is not biogenic in the same sense as, say, coral reefs or peat bogs, and carbonate dissolution can occur abiotically, formation of karst landscapes would not occur in the absence of the biosphere. Seven levels of biogeomorphic biotic-abiotic interactions are identified, from indirect impacts to landforms as extended phenotypes. Karst is generally near the biogenic end of that spectrum, featuring reciprocal interactions and mutual adjustments between biota and landforms and interrelated geomorphological and ecological processes. Karst biogeomorphology may also involve niche construction. In many cases biogeomorphic ecosystem engineering in karst is contingent, in the sense that the engineer organisms may have no, or different, biogeomorphic impacts in non-karst environments. Several examples of contingent ecosystem engineering in karst are given, including biogeomorphic effects of chinkapin oak. Abiotic geomorphic features exist on Earth, but consideration of landform types lying between the biotic-abiotic extremes would likely yield broadly similar conclusions to those about karst. However, it is also clear that we know very little about niche construction and coevolution in karst biogeomorphology, and whether karst or any specific karst features can be considered an extended (composite) phenotype is still an open question. Thus far, most work on biogeomorphology and ecosystem engineering has focused on what might be called obligate engineers—organisms whose engineering effects are at least inevitable, if not necessary to their survival. However, in some cases contingent ecosystem engineers have substantial geomorphic impacts.
    Keywords: Karst ; Biogeomorphology ; Contingent Ecosystem Engineering ; Niche Construction ; Biotic-Abiotic Interactions ; Environmental Sciences ; Geography ; Oceanography
    ISSN: 0309-1333
    E-ISSN: 1477-0296
    Source: Sage Journals (Sage Publications)
    Source: SAGE HSS (Sage Publications)
    Source: SAGE Urban Studies (Sage Publications)
    Source: SAGE Journals (Sage Publications)
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  • 3
    Language: English
    In: Physical Geography, 01 October 2013, Vol.34(4-5), pp.273-292
    Description: This study explores the origin of 15 small coastal watersheds (SCWs) confined entirely to the lower Coastal Plain, which lie between the watersheds of the major rivers flowing across the Texas Coastal Plain. The relationship between SCWs and...
    Keywords: Watershed Fragmentation ; Small Coastal Watersheds ; Texas Coastal Plain ; Avulsion ; Geography
    ISSN: 0272-3646
    E-ISSN: 1930-0557
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  • 4
    Language: English
    In: Progress in Physical Geography: Earth and Environment, December 2018, Vol.42(6), pp.697-720
    Description: Nine axioms for interpreting landscapes from a geoscience perspective are presented, and illustrated via a case study. The axioms are the self-evident portions of several key theoretical frameworks: multiple causality; the law–place–history triad; individualism; evolution space; selection principles; and place as historically contingent process. Reading of natural landscapes is approached from a perspective of place formation. Six of the axioms relate to processes or phenomena: (1) spatial structuring and differentiation processes occur due to fluxes of mass, energy, and information; (2) some structures and patterns associated with those fluxes are preferentially preserved and enhanced; (3) coalescence occurs as structuring and selection solidify portions of space into zones (places) that are internally defined or linked by mass or energy fluxes or other functional relationships, and/or characterized by distinctive internal similarity of traits; (4) landscapes have unique, individualistic aspects, but development is bounded by an evolution space defined by applicable laws and available energy, matter, and space resources; (5) mutual adjustments occur between process and form (pattern, structure), and among environmental archetypes, historical imprinting, and environmental transformations; and (6) place formation is canalized (constrained) between clock-resetting events. The other three axioms recognize that Earth surface systems are always changing or subject to change; that some place formation processes are reversible; and that all the relevant phenomena may manifest across a range of spatial and temporal scales. The axioms are applied to a study of soil landscape evolution in central Kentucky, USA.
    Keywords: Landscape Interpretation ; Place Formation ; Earth Surface Systems ; Spatial Structuring ; Soil Geomorphology ; Environmental Sciences ; Geography ; Oceanography
    ISSN: 0309-1333
    E-ISSN: 1477-0296
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  • 5
    Language: English
    In: Geoderma, 01 April 2016, Vol.267, pp.58-64
    Description: Soil landscapes often exhibit complex spatial patterns, with some aspects of soil variation apparently unrelated to measurable variations in environmental controls. However, these local, contingent complexities are not truly random or intrinsically unknowable. The purpose of this work is to develop and apply a method for identifying or teasing out causes of soil landscape complexity. Soil spatial adjacency graphs (SAG) represent the geography of soil landscapes as a network that can be analyzed using algebraic graph theory. These SAGs include linear sequential subgraphs that represent sequences of soil forming factors. The number and length of these soil factor sequences (SFS), and their associated spectral radius values, determine whether the SFS are sufficient to explain the spatial pattern of soil adjacency. SAGs and associated graph theory methods provide useful tools for guiding pedological investigations and identifying gaps in knowledge. The methods also allow sources of soil landscape complexity and variability to be determined in a way that can help assess the underlying deterministic sources of chaos and dynamical instability in pedology. The approach is applied to a soil landscape in central Kentucky, producing a SAG with 13 nodes (soil types) and 36 links indicating whether the soils occur contiguously. Five SFS were identified, the sum of whose spectral radius values is 6.35. The spectral radius of the SAG is 6.56, indicating that the SFS can explain most, but not all, of the complexity of the soil relationships. The analysis also points to potential environmental controls that could potentially enable full explanation.
    Keywords: Soil Complexity ; Soil Variability ; Spatial Adjacency Graph ; Soil Factor Sequence ; Spectral Radius ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Physical Geography, 04 July 2018, Vol.39(4), pp.304-328
    Description: Tree roots have biogeomorphic engineering effects on epikarst weathering and soil deepening. This is investigated using a system model describing the interactions among biogeomorphic effects of roots, weathering, and soil-epikarst development. The model shows that the system is dynamically...
    Keywords: Biogeomorphology ; Plant-Soil-Weathering Feedbacks ; Epikarst ; Ecosystem Engineering ; Soil Depth ; Geography
    ISSN: 0272-3646
    E-ISSN: 1930-0557
    Source: Taylor & Francis (Taylor & Francis Group)
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  • 7
    In: Earth Surface Processes and Landforms, January 2016, Vol.41(1), pp.16-26
    Description: Biotic influences on geomorphology (and vice‐versa) are ubiquitous. This paper explores whether landforms may be extended (composite) phenotypes of biota, based on four criteria: process–form relationships between biota and landforms; evolutionary synchrony; selective pressure via ecosystem engineering and niche construction; and positive feedback benefitting the engineer organism(s). Coral reefs, peat bogs, biomantles, insect mounds, grassland soils, salt marshes, mangrove swamps, and some vegetation‐dependent sand dune types clearly meet these criteria. Karst landforms, meandering rivers, and tree uprooting pit‐mound systems meet the first three criteria, but positive feedback to engineer organisms has not been established. Research in biogeomorphology will surely identify other extended phenotypes. Implications are that biological evolution will continue to drive landscape metamorphosis, the appearance of new landform types, and presumably the disappearance of extended phenotypes associated with extinct species. Independently of extended phenotypes, tightly‐coupled geomorphological–ecological interactions such as coevolution, and biogeomorphic forms of ecosystem engineering and niche construction are common. The toposphere, encompassing Earth's landforms, is partly a biotic construct. Some elements would be present in an abiotic world, but the toposphere would not exist in anything resembling its contemporary state without a biosphere. This raises important questions with respect to Earth system evolution. The bio, litho‐, atmo‐, hydro‐, topo‐, and pedospheres coevolve at the global scale. Major biotic events have driven revolutions in the other spheres, but the atmosphere and the global hydrological system seem to have been relatively steady‐state at the global scale. The toposphere and pedosphere have not. This suggests that perhaps landforms and soils provide the major mechanisms or degrees of freedom by which Earth responds to biological evolution. Landforms and soils may thus be the ‘voice’ of the biosphere as it authors planetary change, even if clear biotic signatures are lacking. Copyright © 2015 John Wiley & Sons, Ltd.
    Keywords: Biogeomorphology ; Niche Construction ; Extended Phenotype ; Biogenic Landforms ; Toposphere
    ISSN: 0197-9337
    E-ISSN: 1096-9837
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  • 8
    In: Earth Surface Processes and Landforms, November 2014, Vol.39(14), pp.1888-1899
    Description: Active and semi‐active anastomosing Holocene channels upstream of the delta in the lower valley of the meandering Neches River in southeast Texas represent several morphologically distinct and hydrologically independent channel systems. These appear to have a common origin as multi‐thread crevasse channels strongly influenced by antecedent morphology. Levee breaching leads to steeper cross‐valley flows toward floodplain basins associated with Pleistocene meander scars, creating multi‐thread channels that persist due to additional tributary contributions and ground water inputs. Results are consistent with the notion of plural systems where main channels, tributaries, and sub‐channels may have different morphologies and hydrogeomorphic functions. The adjacent Trinity and Sabine Rivers have similar environmental controls, yet the Trinity lacks evidence of extensive anastomosing channels on its floodplain, and those of the Sabine appear to be of different origin. The paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy. Copyright © 2014 John Wiley & Sons, Ltd.
    Keywords: Anastamosing Channels ; Anabranching ; Crevasse ; Neches River ; Path‐Dependence
    ISSN: 0197-9337
    E-ISSN: 1096-9837
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  • 9
    Language: English
    In: Geomorphology, 01 August 2016, Vol.266, pp.66-74
    Description: Scale linkage problems in geosciences are often associated with a hierarchy of components. Both dynamical systems perspectives and intuition suggest that processes or relationships operating at fundamentally different scales are independent with respect to influences on system dynamics. But how far apart is “fundamentally different”—that is, what is the “vanishing point” at which scales are no longer interdependent? And how do we reconcile that with the idea (again, supported by both theory and intuition) that we can work our way along scale hierarchies from microscale to planetary (and vice-versa)? Graph and network theory are employed here to address these questions. Analysis of two archetypal hierarchical networks shows low algebraic connectivity, indicating low levels of inferential synchronization. This explains the apparent paradox between scale independence and hierarchical linkages. Incorporating more hierarchical levels results in an increase in complexity or entropy of the network as a whole, but at a nonlinear rate. Complexity increases as a power of the number of levels in the hierarchy, with and usually ≤ 0.6. However, algebraic connectivity decreases at a more rapid rate. Thus, the ability to infer one part of the hierarchical network from other level decays rapidly as more levels are added. Relatedness among system components decreases with differences in scale or resolution, analogous to distance decay in the spatial domain. These findings suggest a strategy of identifying and focusing on the most important or interesting scale levels, rather than attempting to identify the smallest or largest scale levels and work top-down or bottom-up from there. Examples are given from soil geomorphology and karst flow networks.
    Keywords: Scale Linkage ; Scale Hierarchy ; Graph Theory ; Soil Geomorphology ; Fluviokarst ; Geography ; Geology
    ISSN: 0169-555X
    E-ISSN: 1872-695X
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  • 10
    Language: English
    In: Geomorphology, 2012, Vol.137(1), pp.150-158
    Description: Geomorphic systems consist of coupled subsystems with traits of small-world networks (SWN), characterized by tightly connected clusters of components, with fewer connections between the clusters. Geomorphic systems based on scale hierarchies often exhibit a connected caveman small-world network (CCSWN) structure. SWNs are efficient for linking a large number of components with a relatively small number of links; but effects of CCSWN structure on synchronization and scale linkage have not been examined. Synchronization is analyzed via graph theory and applied to: (1) relationships among three levels of form–process interaction in stream channels; (2) hierarchical relationships of weathering systems at scales from weathering profiles to landscapes; and (3) interactions in fluviokarst systems at the scale of flow processes and of landscape evolution. Relationships among system components are represented as simple unweighted graphs. The largest eigenvalue of the adjacency matrix (spectral radius) reflects the critical coupling strength required to synchronize the system. The second-smallest eigenvalue of the Laplacian of the adjacency matrix (algebraic connectivity) is a measure of the synchronizability. In all examples both are much less than the maximum for networks of the same number of nodes. The sparseness of the networks is the major contributor to the low synchronization, but the specific pattern of connections (“wiring”) is also significant. Where CCSWN structures arise naturally, they help explain how geomorphic effects are transmitted between disparate scales in the absence of obvious scale linkage. Where CCSWNs are an option for representation of geomorphic systems in models and data structures, they will not improve scale linkage, despite the efficiency of SWNs in other respects. Methods developed here can be applied to evaluating alternative spatial data structures or mapping strategies which either increase synchronization, supporting a lumping or aggregation approach, or decrease synchronization, indicating disaggregation or splitting into scale hierarchies.
    Keywords: Scale Linkage ; Synchronization ; Geomorphic Systems ; Connected Caveman Small-World Network ; Stream Channels ; Weathering Systems ; Geography ; Geology
    ISSN: 0169-555X
    E-ISSN: 1872-695X
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