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  • 1
    Language: English
    In: Catena, 2013, Vol.111, pp.98-103
    Description: The spatial pattern of soils and soil properties in soil landscapes is considered here as a function of (1) systematic variation along catenas or associated with spatial patterns of soil-forming factors; and (2) local pseudo-random variations associated with local disturbances or small, unobserved variations in soil-forming factors. The problem is approached at two study sites in the U.S. Atlantic Coastal Plain using algebraic graph theory and the spectral radius of the soil adjacency matrix as a measure of complexity. The matrix is constructed based on the observed spatial contiguity of soil taxa, and soil factor sequences (SFS) are defined for each site based on systematic soil variation associated with variations in parent material, topography, sandy surface thicknesses, and secondary podzolization. The spectral radii of the networks described by the adjacency graphs are compared to those associated with the maximum for a graph of the same size, and the maximum associated with control entirely by variations in soil forming factors. At the Clayroot study site, which is entirely cropland, complexity of the adjacency matrix is less than Λ, the maximum that could be accounted for by the four identified SFS, due to redundant information in the SFS. The Littlefield site, by contrast, has a spectral radius greater than Λ. Here, where about half the site is forested, the contingent variation is likely associated with effects of individual trees on soil morphology. The utility of the adjacency analysis is in identifying whether soil heterogeneity is likely associated with SFS or with contingent factors not captured in SFS. ; p. 98-103.
    Keywords: Topography ; Cropland ; Coastal Plain Soils ; Trees ; Catenas ; Soil Heterogeneity ; Landscapes ; Coastal Plains ; Soil Morphology
    ISSN: 0341-8162
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 2
    Language: English
    In: Catena, October 2018, Vol.169, pp.107-118
    Description: Relative sea-level rise (SLR) raises geomorphic base levels, displaces salt water and tidal or backwater effects inland, and changes the hydrology of aquatic and upland environments. On an all-other-things-being equal basis, we can predict some transitions associated with SLR. However, in real coastal landscapes, all other things are not equal. Factors other than sea-level influence geomorphic, hydrological, and ecological processes and controls, environmental interactions often complicate or obscure process-response relationships, and local disturbances may interrupt or overprint them. In this study relationships among coastal environments in North Carolina, USA were investigated as they respond to changes in multiple environmental gradients driven by relative sea level rise, to determine the extent to which the spatial complexity of landscape response can be explained by environmental gradients. Spatial adjacency graphs reflecting observed patterns of contiguity were derived empirically, and five key environmental gradients related to relative sea-level were identified (elevation, hydroperiod, salinity, vegetation, and process regime). The spectral radius of the spatial adjacency graph indicates a complex system that on the landscape level cannot be described or modeled based on linear gradients or successional relationships. Yet, spectral graph theory measures show that the complexity of the system can be fully explained, in the aggregate, by the five identified gradients, despite some redundancy of information therein. This indicates that coastal responses to SLR should be assessed based on multiscalar, nested environmental gradients rather than a single advancing front of change or linear sequence.
    Keywords: Sea-Level Rise ; Coastal Submergence ; Coastal Environments ; Spatial Adjacency Graph ; Complexity ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 3
    Language: English
    In: Catena, December 2013, Vol.111, pp.98-103
    Description: The spatial pattern of soils and soil properties in soil landscapes is considered here as a function of (1) systematic variation along catenas or associated with spatial patterns of soil-forming factors; and (2) local pseudo-random variations associated with local disturbances or small, unobserved variations in soil-forming factors. The problem is approached at two study sites in the U.S. Atlantic Coastal Plain using algebraic graph theory and the spectral radius of the soil adjacency matrix as a measure of complexity. The matrix is constructed based on the observed spatial contiguity of soil taxa, and soil factor sequences (SFS) are defined for each site based on systematic soil variation associated with variations in parent material, topography, sandy surface thicknesses, and secondary podzolization. The spectral radii of the networks described by the adjacency graphs are compared to those associated with the maximum for a graph of the same size, and the maximum associated with control entirely by variations in soil forming factors. At the Clayroot study site, which is entirely cropland, complexity of the adjacency matrix is less than Λ, the maximum that could be accounted for by the four identified SFS, due to redundant information in the SFS. The Littlefield site, by contrast, has a spectral radius greater than Λ. Here, where about half the site is forested, the contingent variation is likely associated with effects of individual trees on soil morphology. The utility of the adjacency analysis is in identifying whether soil heterogeneity is likely associated with SFS or with contingent factors not captured in SFS.
    Keywords: Soil Spatial Heterogeneity ; Soil-Forming Factors ; Soil Factor Sequences ; Adjacency Matrix ; Spectral Radius ; Soil Landscape Complexity ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 4
    Language: English
    In: Catena, Dec, 2013, Vol.111, p.98(6)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.catena.2013.07.003 Byline: Jonathan D. Phillips Abstract: The spatial pattern of soils and soil properties in soil landscapes is considered here as a function of (1) systematic variation along catenas or associated with spatial patterns of soil-forming factors; and (2) local pseudo-random variations associated with local disturbances or small, unobserved variations in soil-forming factors. The problem is approached at two study sites in the U.S. Atlantic Coastal Plain using algebraic graph theory and the spectral radius of the soil adjacency matrix as a measure of complexity. The matrix is constructed based on the observed spatial contiguity of soil taxa, and soil factor sequences (SFS) are defined for each site based on systematic soil variation associated with variations in parent material, topography, sandy surface thicknesses, and secondary podzolization. The spectral radii of the networks described by the adjacency graphs are compared to those associated with the maximum for a graph of the same size, and the maximum associated with control entirely by variations in soil forming factors. At the Clayroot study site, which is entirely cropland, complexity of the adjacency matrix is less than I, the maximum that could be accounted for by the four identified SFS, due to redundant information in the SFS. The Littlefield site, by contrast, has a spectral radius greater than I. Here, where about half the site is forested, the contingent variation is likely associated with effects of individual trees on soil morphology. The utility of the adjacency analysis is in identifying whether soil heterogeneity is likely associated with SFS or with contingent factors not captured in SFS. Article History: Received 29 April 2013; Revised 8 July 2013; Accepted 11 July 2013
    Keywords: Plains -- Analysis
    ISSN: 0341-8162
    Source: Cengage Learning, Inc.
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  • 5
    Language: English
    In: Catena, Feb, 2015, Vol.125, p.111(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.catena.2014.10.014 Byline: Jonathan Phillips, Daniel A. Marion, Chad Yocum, Stephanie H. Mehlhope, Jeff W. Olson Abstract: We studied tree uprooting associated with an EF2 tornado that touched down in portions of the Ouachita Mountains in western Arkansas in 2009. In the severe blowdown areas all trees in the mixed shortleaf pine-hardwood forest were uprooted or broken, with no relationship between tree species or size and whether uprooting or breakage occurred. There was also no significant relationship between tree species and amount of soil displaced, and only a weak relationship between tree size and rootwad size. Uprooting resulted in a mean bioturbation rate of 205m.sup.3 ha.sup.-1 (about 240tha.sup.-1). Direct transfer of wind energy via tree uprooting to geomorphic work of soil displacement was about 75 to 190Jm.sup.-2. Given the infrequency of tornadoes, this energy subsidy is minor with respect to the long-term energetics of pedogenesis and landscape evolution. However, it does represent a highly significant pulse of geomorphically-significant energy relative to other mechanical processes. Tornadoes such as that of April, 2009 -- not atypical for the region -- are disturbances causing severe, non-selective impacts within the affected area. At a broader, landscape scale, tornadoes are highly localized disturbances, and occur infrequently within any given landform element or forest stand. Only about a third of the uproots revealed root penetration of bedrock, compared to about 90% in other areas of the Ouachita Mountains. This is attributable to the thicker colluvial soils at the study site, and is consistent with the idea that root-bedrock interaction is more likely in thinner regolith covers. Article History: Received 26 February 2014; Revised 19 August 2014; Accepted 16 October 2014
    Keywords: Landscape Evolution ; Tornadoes ; Deciduous Forests
    ISSN: 0341-8162
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Catena, June 2017, Vol.153, pp.168-181
    Description: State-and-transition models (STM) are used to describe, model, interpret, and predict when landscapes will undergo a qualitative state change. Although rangeland ecologists pioneered STMs, geomorphological STM-type models were developed prior to and independently of ecological STMs. This study categorized 47 geomorphological STMs according to whether they were: based on single or multiple study areas; primarily for description and interpretation or predictive and prescriptive use; explicitly concerned with complex system dynamics; and the role of biogeomorphic interactions in the model. Each STM was represented as a graph and the structure identified. Spectral radii were calculated to measure the complexity of each STM. Although STMs are associated with conceptual frameworks that recognize the possibility of nonequilibrium, alternative states, and path dependency, results show that an explicit concern with complexity does not necessarily lead to the identification of more states and transitions, or a more complex transition pattern. The purpose for which a STM was created, as well as the number of study sites it can be applied to, also had little bearing on the models' complexity. This review suggests that geomorphic STMs, rather than being used to fit explanations about landscape evolution into predefined theoretical categories, are veridical representations of empirical observations. Although STMs are particularly useful for grasping the biogeomorphological dynamics of landscapes, this review indicates their utility is not limited to biogeomorphology or to systems with a strong ecological imprint. Time scales involved in geomorphic change can make it difficult to observe a large number of states and transitions, which may constrain what types of STM structure can be identified, as the number of observed states and transitions required to develop particular graph structures varies widely.
    Keywords: State-and-Transition Models ; Geomorphic Systems ; Graph Theory ; Geomorphic Change ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 7
    Language: English
    In: Catena, February 2015, Vol.125, pp.111-119
    Description: We studied tree uprooting associated with an EF2 tornado that touched down in portions of the Ouachita Mountains in western Arkansas in 2009. In the severe blowdown areas all trees in the mixed shortleaf pine–hardwood forest were uprooted or broken, with no relationship between tree species or size and whether uprooting or breakage occurred. There was also no significant relationship between tree species and amount of soil displaced, and only a weak relationship between tree size and rootwad size. Uprooting resulted in a mean bioturbation rate of 205 m ha (about 240 t ha ). Direct transfer of wind energy via tree uprooting to geomorphic work of soil displacement was about 75 to 190 J m . Given the infrequency of tornadoes, this energy subsidy is minor with respect to the long-term energetics of pedogenesis and landscape evolution. However, it does represent a highly significant pulse of geomorphically-significant energy relative to other mechanical processes. Tornadoes such as that of April, 2009—not atypical for the region—are disturbances causing severe, non-selective impacts within the affected area. At a broader, landscape scale, tornadoes are highly localized disturbances, and occur infrequently within any given landform element or forest stand. Only about a third of the uproots revealed root penetration of bedrock, compared to about 90% in other areas of the Ouachita Mountains. This is attributable to the thicker colluvial soils at the study site, and is consistent with the idea that root–bedrock interaction is more likely in thinner regolith covers.
    Keywords: Geomorphic Disturbance ; Bioturbation ; Tornado Blowdown ; Uprooting ; Biogeomorphology ; Ouachita Mountains ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 8
    Language: English
    In: Catena, 2007, Vol.70(1), pp.92-104
    Description: Soils and weathering profiles in a wide variety of parent materials and environmental settings exhibit coarse-over-fine vertical textural contrasts. Where these cannot be attributed to inherited texture contrasts or erosion–deposition, the most common explanations are based on translocation (eluviation–illuviation) which removes clays from surface layers and deposits them in the subsoil; or bioturbation, where preferentially fine material is delivered to the surface by organisms, from whence erosional winnowing creates a coarse surface layer. In some soils of the lower coastal plain of North Carolina, U.S.A., neither explanation is sufficient to explain the observed texture contrasts. A heuristic model based on a combination of translocation of fine material from surface to subsoil, and bioturbation-driven delivery and recycling of material to the surface can explain the observed vertical textural contrasts. The key elements in the model are coastal plain sediments which include some fine material; eluviation–illuviation by percolating water; delivery of additional fine and mixed grain size material to surface by bioturbation, making it available for translocation; concentration of fine material originally scattered throughout the parent material in a B horizon; and maintenance of vertical moisture fluxes by bioturbation. The model is supported by morphological evidence of the key mechanisms, argillic horizons that are finer than both the surface layers and underlying parent material, evidence that argillic horizon formation is not limited by the rate of clay synthesis, and the absence of texture contrasts in nearby soils formed from dune sands which lack fines.
    Keywords: Texture Contrast Soils ; Translocation ; Bioturbation ; Coastal Plain ; Soil ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 9
    Language: English
    In: Catena, 2004, Vol.58(3), pp.275-295
    Description: Coarse-over-fine vertical texture contrasts (VTC) are common in soils and weathering profiles in a variety of environmental settings, including many where inheritance or surficial processes alone cannot account for them. A multiple causality model is presented here which shows that texture contrasts can form in response to a combination of ubiquitous phenomena. There are six key elements: downward translocation by water, erosional winnowing, soil mixing by bioturbation, the tendency for surface clay additions to be mobilized while subsurface clays are more likely to remain in place, and biological facilitation of moisture flux. No element alone is sufficient to create a VTC, but not all are necessary in any given regolith. The model is illustrated by application to case studies in the Ouachita Mountains, Arkansas; ridgetops in eastern Kentucky; the lower coastal plain of North Carolina; and the upper coastal plain of east Texas. The implications for interpretation of soils, paleosols, and weathering profiles is that the presence of a textural contrast, by itself, does not connote any particular set of geogenic or pedogenic processes or controls. Texture contrasts may be geogenic, pedogenic, or both. Given the widespread occurrence of the mechanisms of the multiple causality model, vertical texture contrasts are inevitable.
    Keywords: Vertical Texture Contrasts ; Soil ; Regolith ; Weathering Profile ; Multiple Causality Model ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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  • 10
    Language: English
    In: Catena, 2001, Vol.43(2), pp.101-113
    Description: The spatial structure of soil variability at the landscape scale was examined on adjacent geomorphic surfaces dating from 80 to 200 ka in eastern North Carolina. The purpose was to determine whether there is evidence at broader scales (distances of 10 (super 2) -10 (super 4) m) for the divergent evolution observed in the field at very detailed scales (distances of 10 (super 0) -10 (super 2) m). The state probability function (SPF), which measures spatial dependence for categorical environmental data along a transect, was applied to soil series mapped at a 1:24,000 scale. The older Talbot Terrace and younger Pamlico Terrace surfaces showed distinctly different patterns of spatial variability. The range of spatial dependence was shorter on the older surface (about 200 vs. 300 m), and the SPF was higher at any given distance, indicating more variability. The SPF for the Pamlico surface also indicates a periodicity related to fluvial dissection of the landscape, which is not readily detectable on the Talbot transect despite its greater degree of dissection. The results confirm earlier field studies which suggest that pedogenesis is marked by divergence, whereby differences in initial conditions or local perturbations persist and increase to produce a more variable soil cover.
    Keywords: Pedogenesis ; Pedology ; Scale ; Soil ; Soil Map ; Spatial Analysis ; Sciences (General) ; Geography ; Geology
    ISSN: 0341-8162
    E-ISSN: 1872-6887
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