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Abstract

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 (λ1) 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 (λ1 < 0); neutrally path-stable irreversible progressions (λ1 = 0); path unstable with very low divergence (0 < λ1 < 1); path unstable with low divergence (λ1 = 1); and complex multiple pathways (λ1 > 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 λ1 = 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.
... In this respect, we question the validity of a key premise of the continuum concept: that we can reconstruct the speciation process using many different pairs of populations that differ in their level of RI. The idea of reconstructing long-term processes from contemporary observations is not limited to evolutionary biology and is more generally referred to as chronosequence analysis (Walker et al. 2010;Phillips 2015). Textbook examples include classic ecological studies of plant community succession, in which chronosequences were constructed by comparing vegetation communities across many sites that differ in their age since a common initial condition (e.g., formation of a sand dune, the retreat of a glacier, or time since a disturbance) (Johnson and Miyanishi 2008;Walker et al. 2010). ...
... Textbook examples include classic ecological studies of plant community succession, in which chronosequences were constructed by comparing vegetation communities across many sites that differ in their age since a common initial condition (e.g., formation of a sand dune, the retreat of a glacier, or time since a disturbance) (Johnson and Miyanishi 2008;Walker et al. 2010). Change across these chronosequences has often been adopted as a model indicating the trajectory that any site starting the process will inevitably take if given sufficient time (Walker et al. 2010;Phillips 2015). ...
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A primary roadblock to our understanding of speciation is that it usually occurs over a timeframe that is too long to study from start to finish. The idea of a speciation continuum provides something of a solution to this problem; rather than observing the entire process, we can simply reconstruct it from the multitude of speciation events that surround us. But what do we really mean when we talk about the speciation continuum, and can it really help us understand speciation? We explored these questions using a literature review and online survey of speciation researchers. Although most researchers were familiar with the concept and thought it was useful, our survey revealed extensive disagreement about what the speciation continuum actually tells us. This is due partly to the lack of a clear definition. Here, we provide an explicit definition that is compatible with the Biological Species Concept. That is, the speciation continuum is a continuum of reproductive isolation. After outlining the logic of the definition in light of alternatives, we explain why attempts to reconstruct the speciation process from present‐day populations will ultimately fail. We then outline how we think the speciation continuum concept can continue to act as a foundation for understanding the continuum of reproductive isolation that surrounds us. This article is protected by copyright. All rights reserved
... Spatial adjacency graphs have also been analyzed, where nodes are types of spatial units (for instance soil types or landforms) and links are based on whether those types occur contiguously (e.g. Layeghifard et al., 2015;Phillips, 2015;Danek et al., 2016). Graph methods have also been used to analyze chronosequences or state-and-transition models, with system states or developmental stages as nodes, and transitions between them as links (e.g. ...
... Graph methods have also been used to analyze chronosequences or state-and-transition models, with system states or developmental stages as nodes, and transitions between them as links (e.g. Phillips, 2015Phillips, , 2016Van Dyke, 2015). ...
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Case studies of ecosystem responses to changing climates are necessary in understanding and adapting to these changes. However, more general conceptual frameworks are also needed to contextualize and synthesize case studies, and to provide guidelines for assessment and prediction. This study analyzes a network model of ecological and soil state factor interrelationships to address issues such as sensitivity, resilience, and complexity of climate-driven terrestrial ecosystem changes. A factorial ecosystem model is analyzed using techniques from algebraic graph theory. Results show high values for spectral radius, graph energy, and algebraic connectivity. These indicate complexity, dynamical instability, active reverberating feedbacks, and high synchronization. Implications are that climate effects on ecosystems will be complicated, complex, and difficult to predict. We should be prepared for surprises in the form of unanticipated pathways and outcomes. The inherent nature of ecosystem interconnectivity indicated by the state factor model also suggests that when simulation models and change assessments do turn out to be wrong, it does not necessarily mean the underlying scientific understandings, data, or assumptions are wrong, as sensitivity to relatively minor variations and disturbances is high, and complexity and low predictability are inherent. Ecosystem reactions to climate (and other, often contemporaneous) changes will reverberate through the ecosystem. Both filtering and amplification may occur, but net amplification is indicated by the graph analysis. Ecosystem responses are integrated system responses-state factors will respond as a single integrated unit, not as a collection or sequence of individual responses.
... An important issue, however, that emerges with soil chronosequences is the following: is the deceleration or reversal of process rates, e.g., co-evolution (Phillips, 2015). For instance, in 226 sensitive Alpine environmental areas, a recent acceleration of (geomorphic) processes is 227 measured or postulated, particularly in the permafrost zone where melting subsurface ice leads to changing or repeatedly changing environmental conditions remains a topic that merits further 230 investigation. ...
Article
Clay minerals are among the most chemically active components and are a bridge between the inorganic and organic parts of a soil. The clay minerals influence pedogenetic processes by interacting with cations and inorganic and organic compounds, influencing the nutrition of the plants and the structure of the soils. Clay minerals are phyllosilicates and can in soils be either inherited from the parent material, neoformed, or transformed from precursor minerals. Relatively shortly after exposure of the parent material to atmospheric conditions, important mineral transformation reactions can occur, even in cold alpine climates. In alpine environments, the soil system reacts in a particularly sensitive way at the beginning of soil formation, i.e. during the first c. 3000 years. With time, the formation and transformation rates, and thus changes, decelerate. Smectitic components, and therefore 2:1 mineral structures, are the weathering steady-state products. Although weathering conditions are particularly intense close to the timberline and on pole-facing sites, 2:1 minerals strongly prevail over kaolinite or gibbsite, which are most often encountered as a weathering steady-state product in tropical regions. Smectitic components enrich under conditions of high percolation rates, cool climates (close to the treeline), high amounts of organic ligands, low erosion, stable conditions, and thus low soil production rates. Smectite formation therefore relates not only to the paradigms of the percolation theory, but the type and presence of vegetation and the production of organic ligands are additional driving factors.
... These chronosequences are currently under-studied, but they constitute unique and ideal sites for testing various theories in restoration ecology. However, the interpretation of from chronosequence data requires caution due to potential pitfalls and confounding factors, including the space-for-time assumption and spatial variability (Walker et al., 2010;Phillips, 2015). ...
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Degraded post-mining landscapes exhibit unique biotic and abiotic components and processes relative to pre-disturbance natural ecosystems. Yet the concept of pre-disturbance reference natural ecosystems and their associated soil quality indicators (SQIs) (e.g., pH, soil organic carbon) are prominently used for assessing restoration of post-mining landscapes. Limited reviews exist on the validity, limitations, opportunities and knowledge gaps associated with the application of the concept and SQIs on post-mining landscapes. Hence, evidence was examined to highlight constraints, opportunities and future research directions pertaining to the concept and SQIs. First, as novel, hybrid or designer ecosystems, severely degraded post-mining landscapes lack reference natural ecosystems. The framing of restoration is multi-dimensional, and dependent on spatial and temporal scales. Therefore, short-term data on SQIs often measured at point scale cannot adequately account for the multi-dimensionality and scales. Moreover, evidence linking SQIs to ecosystem functions, goods, values, services and benefits on degraded post-mining landscapes remains weak. Potential redundancy exists among SQIs, because soil properties exhibit spatial and temporal correlation. The universality of SQIs remains unconfirmed, because data validating the measurement protocols and interpretation of SQIs across various biomes are scarce. A framework is presented proposing: (1) a shift from the concept of reference natural ecosystems to novel and designer ecosystems in restoration ecology, (2) the development of the next generation of hierarchical or ecosystem cascade indicators, and end-points addressing the multi-dimensionality and scale issues, and (3) a decision matrix for integrating novel, hybrid and designer ecosystems. The potential applications of novel tools such as drones, laser-based cameras, genomics and big data analytics are highlighted. Such novel tools could unravel the complex linkages among biotic and abiotic components, and ecosystem function and services, which are currently difficult to investigate using conventional techniques. Finally, ten tentative hypotheses are presented on the restoration of degraded post-mining landscapes.
... It is well known that the application of this chronosequence concept has some limitations. The assumption that time is the only factor affecting soil development in a spatial sequence of soils is rarely valid but the only option for a detailed historical tracking of landscape development at a particular location (Phillips, 2015). We therefore have to assume that differences in topography and elevation among the selected moraines only lead to moderate differences in soil hydrologic conditions. ...
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Soil physical properties highly influence soil hydraulic properties, which define the soil hydraulic behavior. Thus, changes within these properties affect water flow paths and the soil water and matter balance. Most often these soil physical properties are assumed to be constant in time, and little is known about their natural evolution. Therefore, we studied the evolution of physical and hydraulic soil properties along two soil chronosequences in proglacial forefields in the Central Alps, Switzerland: one soil chronosequence developed on silicate and the other on calcareous parent material. Each soil chronosequence consisted of four moraines with the ages of 30, 160, 3000, and 10 000 years at the silicate forefield and 110, 160, 4900, and 13 500 years at the calcareous forefield. We investigated bulk density, porosity, loss on ignition, and hydraulic properties in the form of retention curves and hydraulic conductivity curves as well as the content of clay, silt, sand, and gravel. Samples were taken at three depths (10, 30, 50 cm) at six sampling sites at each moraine. Soil physical and hydraulic properties changed considerably over the chronosequence. Particle size distribution showed a pronounced reduction in sand content and an increase in silt and clay content over time at both sites. Bulk density decreased, and porosity increased during the first 10 millennia of soil development. The trend was equally present at both parent materials, but the reduction in sand and increase in silt content were more pronounced at the calcareous site. The organic matter content increased, which was especially pronounced in the topsoil at the silicate site. With the change in physical soil properties and organic matter content, the hydraulic soil properties changed from fast-draining coarse-textured soils to slow-draining soils with high water-holding capacity, which was also more pronounced in the topsoil at the silicate site. The data set presented in this paper is available at the online repository of the German Research Center for Geosciences (GFZ; Hartmann et al., 2020b). The data set can be accessed via the DOI https://doi.org/10.5880/GFZ.4.4.2020.004.
... Soil erosion is generally driven by tectonic activity, parent material, surface topography, climate, anthropogenic and biotic activity (Smithson et al., 2008) some of these factors may vary over time. Changing environmental conditions can lead to an acceleration, deceleration or reversal of erosion and soil formation rates: a factor constellation that gives rise to co-evolution (Phillips, 2015). These varying constellations over time are, owing to methodological restrictions, difficult to decipher. ...
Article
Forested areas are assumed not to be influenced by erosion processes. However, forest soils of Northern Germany in a hummocky ground moraine landscape can sometimes exhibit a very shallow thickness on crest positions and buried soils on slope positions. The question consequently is: Are these on-going or ancient erosional and depositional processes? Plutonium isotopes act as soil erosion/deposition tracers for recent (last few decades) processes. Here, we quantified the ²³⁹⁺²⁴⁰Pu inventories in a small, forested catchment (ancient forest “Melzower Forst”, deciduous trees), which is characterised by a hummocky terrain including a kettle hole. Soil development depths (depth to C horizon) and ²³⁹⁺²⁴⁰Pu inventories along a catena of sixteen different profiles were determined and correlated to relief parameters. Moreover, we compared different modelling approaches to derive erosion rates from Pu data. We find a strong relationship between soil development depths, distance-to-sink and topography along the catena. Fully developed Retisols (thicknesses > 1 m) in the colluvium overlay old land surfaces as documented by fossil Ah horizons. However, we found no relationship of Pu-based erosion rates to any relief parameter. Instead, ²³⁹⁺²⁴⁰Pu inventories showed a very high local, spatial variability (36–70 Bq m⁻²). Low annual rainfall, spatially distributed interception and stem flow might explain the high variability of the ²³⁹⁺²⁴⁰Pu inventories, giving rise to a patchy input pattern. Different models resulted in quite similar erosion and deposition rates (max: −5 t ha⁻¹ yr⁻¹ to +7.3 t ha⁻¹ yr⁻¹). Although some rates are rather high, the magnitude of soil erosion and deposition - in terms of soil thickness change - is negligible during the last 55 years. The partially high values are an effect of the patchy Pu deposition on the forest floor. This forest has been protected for at least 240 years. Therefore rather natural events and anthropogenic activities during medieval times or even earlier must have caused the observed soil pattern, which documents strong erosion and deposition processes.
... Geophysical techniques associated with field and laboratory investigations could be used to define, with high accuracy, the occurrence of high-alumina clay areas. This is because soil cover shows pronounced lateral variability and discontinuity on the slope, based on soil moisture and influenced by shallow groundwater (Nahon 1991a;Phillips 2015). ...
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Mottled and high-alumina clay horizons (Gleysols) above dismantled iron crusts (Ferralsols) are widespread in the soils that developed on the flat sedimentary plateau located in western Minas Gerais State (Brazil). Field exploration shows that the deposits of high-alumina clays are located at a lower topographic position, mottled horizons suggesting a lateral transformation system. Two-dimensional and pseudo-three-dimensional electrical resistivity tomography (ERT) techniques have been tested to investigate the distribution of high-alumina clay layers in a thick lateritic mantle, and to assess the potential of the technique to delimitate ore reserves. The figures of resistivity, based on spatial variations of electrical properties of the weathering layers, showed spatial changes in the subsurface structure of weathering mantle, expanding the distribution of iron crust and the high-alumina clay layers, which are strongly influenced by aquifer. Combining 2D and pseudo-3D geophysical images with soil morphology and geochemistry, we delimitate the high-alumina clay layer and discuss its genesis. The ore is located exclusively on the edge of the plateau and is closely linked to the development of hydromorphic soils, exactly where the vertical water flow is restrained by the iron crust. This distinct water regime defines the geochemical transfers in soil mantle, depleting Fe2O3 from Gleysol and correspondingly increasing Al2O3 and SiO2. This study aimed to evaluate the potential of ERT as a prospecting tool for supergene ore, and as a technique with reduced environmental impact in the mineral research, when compared to the pre-existing exploration methods (trenches, drill holes and extraction) that are applied on this sensitive wetland system in which high-alumina clays may occur.
Chapter
History matters. Global (independent of place and time) principles are necessary to explain landscape evolution, as are place factors (geographical and environmental context). But, by themselves, they are not sufficient. To explain landscape evolution—which by definition has important temporal dimensions—history must also be incorporated. Landscape evolution is historically contingent. This chapter outlines several different types of historical contingency, discusses multiple pathways and outcomes in landscape evolution, and evaluates why some imaginable pathways are rare and others common, and some trends are divergent and others convergent. Methods for evaluating path stability of historical trajectories are introduced and applied to several different Earth surface systems. The chapter concludes with a consideration of landscape evolution in the context of convergence, divergence, and equifinality.
Chapter
Clay minerals are among the most chemically active components and are a bridge between the inorganic and organic parts of a soil. The clay minerals influence pedogenetic processes by interacting with cations and inorganic and organic compounds, influencing the nutrition of the plants and the structure of the soils. Clay minerals are phyllosilicates and can in soils be either inherited from the parent material, neoformed, or transformed from precursor minerals. Relatively shortly after exposure of the parent material to atmospheric conditions, important mineral transformation reactions can occur, even in cold alpine climates. In alpine environments, the soil system reacts in a particularly sensitive way at the beginning of soil formation, i.e. during the first c. 3000 years. With time, the formation and transformation rates, and thus changes, decelerate. Smectitic components, and therefore 2:1 mineral structures, are the weathering steady‐state products. Although weathering conditions are particularly intense close to the timberline and on pole‐facing sites, 2:1 minerals strongly prevail over kaolinite or gibbsite, which are most often encountered as a weathering steady‐state product in tropical regions. Smectitic components enrich under conditions of high percolation rates, cool climates (close to the treeline), high amounts of organic ligands, low erosion, stable conditions, and thus low soil production rates. Smectite formation therefore relates not only to the paradigms of the percolation theory, but the type and presence of vegetation and the production of organic ligands are additional driving factors.
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This book provides a theory to overcome the problem of identifying the principles behind the interdependence of different aspects of nature. Climate, vegetation, geology, landforms, soils, hydrology, and other environmental factors are all linked. Many scientists agree that there must be some general principles about the way in which earth surface systems operate, and about the ways in which the interactions of the biosphere, lithosphere, hydrosphere, and atmosphere manifest themselves. Yet there may be inherent limits on our ability to understand and isolate these interactions using traditional reductionist science. The argument of this book is that the simultaneous presence of order and chaos reflects fundamental, common properties of earth surface processes and systems. It shows how and why this is the case, with examples ranging from evolutionary and geological times scales to microscale examinations of process mechanics.
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Models of karstification based on the physics of fluid flow in fractures of soluble rock, and the physical chemistry of dissolution of limestone by CO2 containing water have been presented during the last two decades. This paper gives a review of the basic principles of such models, their most important results, and future perspectives. The basic element of evolving karst systems is a single isolated fracture, where a constant hydraulic head drives calcite aggressive water from the input to the output. Non linear dissolution kinetics with order n = 4 induce a positive feedback by which dissolutional widening at the exit enhances flow rates thus increasing widening and so on until flow rates increase dramatically in a breakthrough event. After this the hydraulic head breaks down and widening of the fracture proceeds fast but even along its entire length under conditions of constant recharge. The significance of modelling such a single fracture results from the fact that an equation for the breakthrough time specifies the parameters determining the processes of early karstification. In a next step the boundary conditions for isolated fractures are varied by including different lithologies of the rock, expressed by different dissolution kinetics. This can enhance or retard karstification. Subterranean sources of CO2 can also be simulated by changing the equilibrium concentration of the solution at the point where CO2 is injected. This leads to accelerated karstification. At the confluence of solutions from two isolated tubes into a third one, mixing corrosion can release free carbon dioxide. Its effect to solutional widening in such a system of three conduits is discussed. Although these simple models give interesting insights into karst processes more realistic models are required. Combining single fractures into two-dimensional networks models of karst in its dimensions of length and breadth under constant head conditions are presented. In first steps the Ford-Ewers' high-dip and low-dip models are simulated. Their results agree to what one expects from field observations. Including varying lithologies produces a variety of new features. Finally we show that mixing corrosion has a strong impact on cave evolution. By this effect micro climatic conditions in the catchment area of the cave exert significant influence. A common feature in the evolution of such two-dimensional models is the competition of various possible pathways to achieve breakthrough first. Varying conditions in lithologies, carbon dioxide injection or changing hydrological boundary conditions change the chances for the competing conduits. Karst systems developing at steep cliffs in the dimensions of length and depth are characterized by unconfined aquifers with constant recharge to the water table. Modelling of such systems shows that dissolution of limestone occurs close to the water table. The widening of the fractures there causes lowering of the water table until it becomes stable when base level is reached, and a water table cave grows headwards into the aquifer. When prominent deep fractures with large aperture widths are present deep phreatic loops originate below the water table. A river or a lake on a karst plateau imposes constant head conditions at this location in addition to the constant recharge from meteoric precipitation. In this case a breakthrough cave system evolves along the water table kept stable by the constant head input. But simultaneously deep phreatic loops arise below it. In conclusion we find that all cave theories such as those of Swinnerton (1932), Rhoades and Sinacori (1941), and the Four-state-model of Ford are reconciled. They are not contradictory but they result from the same physics and chemistry under different boundary conditions.
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The classic account of primary succession inferred from a 220-yr glacial retreat chronosequence at Glacier Bay National Park, Alaska was compared to reconstructions of stand development based on tree-ring records from 850 trees at 10 sites of different age. The three oldest sites (deglaciated prior to 1840) differ from all younger sites in the early recruitment of Sitka spruce (Picea sitchensis), the presence of western hemlock (Tsuga heterophylla), and the inferred importance of early shrub thickets. The nitrogen-fixing shrub Sitka alder (Alnus sinuata) has been an important and long-lived species only at sites deglaciated since 1840. Black cottonwood (Populus trichocarpa) has been an overstory dominant only at sites deglaciated since 1900. These single-species additions or replacements distinguish three pathways of vegetation compositional change which are segregated spatially and temporally. The communities of different age at Glacier Bay do not constitute a single chronosequence and should nut be used uncritically to infer long-term successional trends. Among-site differences in texture and lithology of soil parent, material cannot account for the multiple pathways. However, distance from each study site to the closest seed source of Sitka spruce at the time of deglaciation explains up to 58% of the among-site variance in early spruce recruitment. Multiple pathways of compositional change at Glacier Bay appear to be a function of landscape context, which, in conjunction with species life history trails (dispersal capability and generation time), affects seed rain to newly deglaciated surfaces and thereby alters the arrival sequence of species. Differences among the pathways probably include long-term differences in ecosystem function resulting from substantial accumulation of nitrogen at sites where nitrogen-fixing shrubs are important.
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Environmental Change explores the nature, causes, rates and directions of environmental change throughout earth history. Huggett introduces the interdependent parts of the natural environment - cosmic, ecological, geological - and the dynamic nature of the environmental system. Integrating a wealth of examples and illustrations from around the world, the book examines evidence and causes of change in life, climate (air and water), soils, sediments and landforms, and the impacts of human-environment interaction.
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Twenty-four soil pedons on each of four sandy lake terraces in northwestern lower Michigan that ranged in age from 3000 to 11 000 yr BP were studied to assess trends in soil morphological variability with time. E horizons attained high color values (lightness) by 3000 yr and changed little after that time, whereas B horizons continued to get darker with time. Cementation within B horizons increased in strength and amount with time, as did B horizon thickness. Soils ≥4000 yr old had deeper eluvial zones but much greater variabilities in the thickness of that zone. Soil development increased with time, but spatial variability in degree of development also increased. These patterns are best explained by invoking spatially random soil mixing upon a surface that is otherwise undergoing podzolization. -from Authors
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Nonlinear dynamical systems models of soil systems suggest that soil evolution may be potentially chaotic, and thus sensitive to initial conditions and to small perturbations. This hypothesis was tested by comparing the diversity of soil types on either side of the Suffolk Scarp on the lower Coastal Plain of North Carolina, the Pamlico Terrace and the Talbot Terrace. A soil system model based on vertical clay distribution and textural differentiation is introduced to account for the major factors that lead to differentiation of soil series in the study area. Only one soil series was indentified on the Pamlico site, while the Talbot transect included at least seven distinct soil series. The dramatically higher variability of the soil cover on the older landscape is predicted by the model and provides field evidence for chaotic pedogenesis. -from Author
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Large sandmasses made up of overlapping systems of parabolic dunes are a feature of the subtropical coast of eastern Australia. The sands were deposited intermittently during the Holocene and Pleistocene as systems of large parabolic dunes aligned with the onshore, southeast winds. Once the dunes were covered by vegetation, they gradually developed secondary geomorphic features at the expense of their primary aeolian form. The six dune systems show that, with age, aeolian shapes are gradually lost, landforms due to water erosion become dominant, weathering eventually proceeds to depths of more than 20m and giant soil profiles form.-from Author
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This book investigates the structure and function of geoecosystems. It does so using a simple dynamic systems model, the "brash' equation, as a conceptual and analytical tool. In brief, the "brash' equation is a set of equations describing the dynamics of the geoecosphere. The geoecosphere is defined as interacting terrestrial life and life support systems - the biosphere, toposphere, atmosphere, pedosphere, and hydrosphere. The rate of change of each component depends on the state of all the others, plus the effect of cosmic, geological, and other forcing factors. The book is divided into three parts. Part one introduces geoecosystems, describing their nature, hierarchical structure, and ideas about their interdependence and integrity. Part two explores the internal (ecological) interactions between geoecosystems and their near-surface environment. Chapters deal with the environmental factors listed in the "brash' equation.: climate and soils; climate and life; altitude; substrate; topography; and insularity. Part three prospects the role of external factors (ecological, geological, and cosmic) as agencies disturbing the dynamics of geoecosystems. -from Author
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Background: Plant succession and community assembly following different land-use histories in the Amazon Basin are poorly understood. Aims: Changes in woody vegetation were monitored across chronosequences of abandoned pastures and abandoned clearcuts in order to compare their successional patterns. Methods: In chronosequences, initially 5–19 years old in abandoned clearcuts and 2–11 years old in abandoned pastures, trees (≥ 3 cm dbh) were tagged and recruitment and mortality recorded annually for 12 years. Results: Stem densities exhibited no significant trend during the first 25 years of succession regardless of land-use history. Basal area in abandoned clearcuts increased rapidly in the first decade, outpacing accumulation in abandoned pastures, although basal area on the two pathways converged at 25 years post-abandonment. Transects in abandoned pastures were much more variable in stem density and basal area than those in abandoned clearcuts, reflecting cohort growth and thinning by the dominant genus Vismia in the pastures. Species density, initially similar in the young stands, increased at a much faster rate in abandoned clearcuts than in abandoned pastures, resulting in a large divergence after 25 years. Conclusions: Succession following deforestation in the Amazon exhibits alternative pathways that correspond to prior land use – abandoned clearcuts of primary forest or clearcuts converted to pastures through prescribed burns and later abandoned. The most important divergence in the two successions was the extremely slow accumulation of species over 25 years in abandoned pastures.
Book
This book investigates the structure and function of geoecosystems. It does so using a simple dynamic systems model, the "brash' equation, as a conceptual and analytical tool. In brief, the "brash' equation is a set of equations describing the dynamics of the geoecosphere. The geoecosphere is defined as interacting terrestrial life and life support systems - the biosphere, toposphere, atmosphere, pedosphere, and hydrosphere. The rate of change of each component depends on the state of all the others, plus the effect of cosmic, geological, and other forcing factors. The book is divided into three parts. Part one introduces geoecosystems, describing their nature, hierarchical structure, and ideas about their interdependence and integrity. Part two explores the internal (ecological) interactions between geoecosystems and their near-surface environment. Chapters deal with the environmental factors listed in the "brash' equation.: climate and soils; climate and life; altitude; substrate; topography; and insularity. Part three prospects the role of external factors (ecological, geological, and cosmic) as agencies disturbing the dynamics of geoecosystems. -from Author