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The Robustness of Chronosequences
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.
... The decrease in bulk density with an increase in time since emplacement (Figure 2) was one of the strongest and most statistically significant trends observed in the current work, and is consistent with previous work on pedogenetic trends of natural [10,[33][34][35] and anthropogenically impacted [36][37][38][39] soils. Bulk density is primarily a function of organic matter content, soil texture (i.e., particle size distribution), and porosity and is ...
... The decrease in bulk density with an increase in time since emplacement (Figure 2) was one of the strongest and most statistically significant trends observed in the current work, and is consistent with previous work on pedogenetic trends of natural [10,[33][34][35] and anthropogenically impacted [36][37][38][39] soils. Bulk density is primarily a function of organic matter content, soil texture (i.e., particle size distribution), and porosity and is generally higher when mine soils have low organic content, high clay content, and are compacted [40,41]. ...
Anthropogenic changes to soil properties and development can dominate soil systems, particularly in coal mining-impacted landscapes of the Appalachian region of the United States. Historical mining operations deposited spoils which are developing into mine soils in chronosequences, allowing for a correlation between emplacement age and rates of change in soil properties. The study site was in the Huff Run Watershed (Mineral City, OH, USA) with a series of eleven spoil piles that were deposited over a 30-year time period. Surface soils were analyzed for bulk density, loss on ignition (LOI) as a proxy for organic matter, particle size, and bulk mineralogical (by X-ray diffraction) and elemental (by X-ray fluorescence) compositions. The following linear trends were observed across the transect from older to younger mine soils: bulk density increased from 1.0 cm−3 to 1.5 g cm−3; LOI decreased from ~20% to 5%; the content of sand-sized particles and quartz decreased from ~50% to 30% and 50% to 25%, respectively, with a corresponding increase in the contribution of clay mineral from ~25% to 60%; and Fe and other trace metals (Cu, Ni, Pb, Sb, Sn, and Te) decreased in concentration, while Al, Mg, and K increased in concentration. These trends are likely the result of: (1) organic matter accumulation as vegetation becomes more abundant over time; (2) transport of clays out of more recently emplaced waste; and (3) oxidative dissolution of primary sulfides releasing Fe and other trace metals followed by re-precipitation of secondary Fe-phases and trace metal sequestration. The findings presented here provide insight into the future behavior of these materials and can potentially be used to assess the inferred age of previously unexamined mine soils across a wider geographic area. These results can also inform decisions related to reclamation activities and ecosystem restoration.
... Chronosequences, that is, space-for-time substitutions, are fundamental tools for studying environmental changes in a spatial sequence of soils in which the only factor of formation that varies is the age of the surface on which the soil was formed (Phillips, 2015 et al. (2018) used a chronosequence approach to assess reclamation of gold-mining tailings and determined that the organic carbon accumulation is restricted in the long term by the total nitrogen content. ...
... One of the most widely accepted approaches to studying Technosol transformations involves the arrangement of a chronosequence that consists of unweathered deposits and sites of increasing age in which the parent material is more altered (Phillips, 2015). However, in the case of dredged-sediment landfills, it should be kept in mind that these are intrinsically highly heterogeneous as (1) the deposition F I G U R E 3 Loading plot of the first two axes of the spatial principal component analysis using the soil properties pH, N, OM, P, K, Ca, Mg, Na, sand, silt, clay measured in the four areas undergoing reclamation after 4 (T4), 8 (T8), and 12 (T12) years, as well as the unreclaimed (T0) dredgedsediment landfill. ...
Active reclamation is often necessary to ensure a transformation of mining waste into Technosols—“soils dominated or strongly influenced by human‐made material”—and restore its utility and environmental value. The objective of this study is to assess the spatial variation of the physicochemical properties relevant for reclamation and Technosol formation on dredged‐sediment landfills left by alluvial gold mining in a chronosequence of reclamation (0, 4, 8, and 12 years). We hypothesize a higher spatial dependency of most soil properties with increasing time of Technosol formation and an overall homogenization of the soil resulting from pedogenetic processes. Our results show early signs of Technosol pedogenesis with strong physicochemical changes after only few years of formation. We observed that older Technosols (>4 years) are more acidic, have less nutrient and organic matter content, higher exchangeable cations, and less signs of compaction than nonrevegetated landfills. The content of organic matter, phosphorus, and exchangeable cations show the highest spatial variability in Technosols of all ages. In older Technosols, most soil properties showed less spatial variability than in younger Technosols. A multivariate geostatistical approach allowed the delineation of zones with distinctive physicochemical properties within areas of the chronosequence. The results show that reclamation and Technosol formation lead to spatially dependent fragmentation processes reflected in more and smaller clustered zones in Technosols after 12 years of formation. From the perspective of reclamation management, understanding the spatial variability of highly heterogeneous Technosols where substantial changes can be observed within small distances can support the development of site‐specific reclamation strategies suitable to the characteristics of each field as well as the determination of its potential uses.
... 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). ...
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.
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... The soil chronosequence, which reveals the rates and directions of pedogenic change, is a valuable indicator for testing pedogenic theories [1,4,5]. For example, the soil chronosequence is used for gauging chronologically progressive or regressive developments of soil properties and the developments that reach a steady state or rarely reach a kind of near steady state [1,[5][6][7]. Soil chronosequences also show that the genetic pathways of soils under varied climatic conditions are required for the evolution of a specific kind of soil [1,[8][9][10]. ...
Pedogenetic features of the soils could be a proxy for revealing the landform surface processes. Our work first analyzed the particle size distributions and lithological discontinuities (LDs) of the soils in the midstream of the Zoushui River, central Taiwan. The results showed that the parental materials of the soils derive from mixed sediments of the Zoushui River and its tributaries, and the LDs of some soils suggested multi-depositional events with homogeneous lithology. Then, we proposed a soil chronosequence of Inceptisols, Ultisols, and Oxisols, over the Pleistocene timescale. There was a very well-defined semilogarithmic relationship between weighted profile development index (WPDI) values and soil age with correlation coefficients (r) greater than 0.9. The age of the soils did not certainly agree with the interglacials of the main marine isotope stage (MIS). However, the soils started to develop only after being aggraded by relatively warm and humid periods or by extreme rain events in cool and dry periods. Irrespective of whether the soils had started to develop, tectonic downcutting, providing clear altitudinal separation of the terrace treads, could inevitably happen later (or almost synchronologically) to ensure stabilities of the tread surfaces .
... 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. ...
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). ...
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.
Soil hydrologic processes play an important role in the hydro-pedo-geomorphological feedback cycle of landscape evolution. Soil properties and subsurface flow paths both change over time, but due to a lack of observations, subsurface water flow paths are often not properly represented in soil and landscape evolution models. We investigated the evolution of subsurface flow paths across a soil chronosequence in the calcareous glacier forefield at the Griessfirn glacier in the Swiss Alps. Young soils developed from calcareous parent material usually have a high pH value, which likely affects vegetation development and pedogenesis and thus the evolution of subsurface flow paths. We chose four glacial moraines of different ages (110, 160, 4 900, and 13 500 years) and conducted sprinkling experiments with the dye tracer Brilliant Blue on three plots at each moraine. Each plot was divided into three equal subplots, and dyed water was applied with three different irrigation intensities (20, 40, and 60 mm h-1) and an irrigation amount of 40 mm. Subsequent excavation of soil profiles enabled the tracing of subsurface flow paths. A change in flow types with increasing moraine age was observed from a rather homogeneous matrix flow at 110 and 160 years to heterogeneous matrix and finger-shaped flow at 4 900 and 13 500 years. However, the proportion of preferential flow paths is not necessarily directly related to the moraine age but rather to soil properties such as texture, soil layering, organic matter content, and vegetation characteristics such as root length density and biomass. Irrigation intensity had an effect on the number of finger-shaped flow paths at the two old moraines. We also found that flow paths in this calcareous material evolved differently compared to a previous study in siliceous material, which emphasizes the importance of parent material for flow path evolution. Our study provides a rare systematic dataset and observations on the evolution of vertical subsurface flow paths in calcareous soils, which is useful to improve their representation in the context of landscape evolution modeling.
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.
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.
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.
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.
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.
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.
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
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
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
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
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.
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