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Bulk Density, Mean Shear Strength, Mean Grain Size, Percent Texture Classes, and Unsaturated Hydraulic Conductivity for Soil Samples Collected From Different Microtopographic Locations at Each Site
Source publication
Vegetation bands are periodic bands of vegetation, separated by
interband spaces devoid of vegetation, oriented parallel to the
topographic contour in some gently sloping arid to semiarid
environments. Models of vegetation band formation attribute their
formation to positive feedbacks among vegetation density, soil
porosity/permeability, and infilt...
Contexts in source publication
Context 1
... Results from the soil sample analyses indicate that surface soils within the vegetation bands (mound and mound at veg microtopographic locations) are significantly different than those in interband spaces (playa and playa in band microtopographic locations; Table 1). In general, surface soils in the interband spaces have higher bulk densities and shear strengths than those in the vegetation bands. ...
Context 2
... sur- face soils within the interband spaces include more clay and silt than soils within the vegetation bands, while soils within vegetated bands have higher mean grain sizes and higher sand percentages. Values of K follow the grain size and shear strength data (Table 1), i.e., lower K values and higher K values correspond to stronger and finer interband soils and weaker and coarser vegetated band soils, respec- tively. It should be noted that the bulk densities reported for sites within the vegetation bands are maximum estimates because these soils have many low-bulk-density areas (void spaces formerly occupied by plant roots, animal burrows, etc.) that cannot be accurately sampled because emplacing the sampling ring into the soil caused the soil to collapse. ...
Citations
... A number of subsequent mathematical models (e.g., Klausmeier 1999;von Hardenberg et al. 2001;Rietkerk et al. 2002;Gilad et al. 2004Gilad et al. , 2007von et al. 2010;Kletter et al. 2009) are based on the water redistribution hypothesis. Moreover, it is point out that another class of models (e.g., Pelletier et al. 2012;Lefever and Lejeune 1997;Lefever et al. 2009;Martínez-García et al. 2014) have studied as alternative pattern formation mechanisms. Indeed, these various mathematical models are strategically effective for the continuing ecological debates on the key factor of vegetation spatial patterns. ...
Banded vegetation pattern is a striking feature of self-organized ecosystems. In particular, vegetation patterns in semi-arid ecosystems are typical on hillsides, orienting parallel to the contours. The present study concerns a system of coupled reaction–advection–diffusion equations model for this phenomenon and studies the existence and stability of periodic traveling waves in a one-parameter family of solutions. Specifically, we consider a parameter region in which vegetation patterns occur and subdivide into stable and unstable regions as solutions of the model equations. Our numerical results show that the periodic traveling wave changes their stability by Eckhaus (sideband) bifurcation. We discuss the variations of the wavelength, wave speed as well as the conditions of the rainfall parameter by using linear analysis. We also explore how the solution patterns grow when the bifurcation parameter is changing slowly. In order to compare this result with the spatiotemporal pattern in the direct simulation, we show that when it passes a critical value of rainfall parameter a stable pattern becomes unstable and finally disappear. In addition, we investigate the existence and stability of periodic traveling waves as a function of water transport parameter.
... These are determined by resources like radiation, water, nutrients supply and environmental conditions such as temperature, soil acidity, air pollution and human activities. Vegetation patterns occur in many semi-arid regions of the world, including Africa [1,2], Australia [3,4], North America [5,6], the Middle East [7,8], and Asia [9]. Such patterns consist of vegetated regions separated by bare ground. ...
... It is likely that some level of structure exists between MT and heterogeneity of infiltration capacity due to small scale morphological and pedological processes (Rossi & Ares, 2017), that are intertwined with vegetation. For certain systems, MT depressions can be less pervious than the average surrounding soil, for example, due to deposition of fine material and crust formation (Pelletier et al., 2012), which may skew the hydrological balance towards evaporation, rather than infiltration. In systems with increased hydraulic conductivity in puddles, for example, due to higher soil moisture, the effect of MT will be further enhanced. ...
Microtopography (MT) can govern runoff dynamics as a net result of local heterogeneities in the flow paths and ponding. This in turn controls the development of the surface water layer that connects and flows downslope. It is therefore important to understand which microtopographic features affect runoff generation dynamics and its macroscopic—hillslope scale—hydrological signatures (e.g., hydrographs, runoff and infiltration volumes). In this study, we numerically solve 2D overland flow from a single rain pulse on 1,460 idealized hillslopes with different slopes and sinusoidal microtopographies and different infiltration capacities. We assess hydrodynamic distributions, hydrographs and hydrological indices to assess the effects of MT and infiltration on the (local) hydrodynamic and (larger scale) hydrologic responses in terms of surface runoff regimes. The results show that MT enhances infiltration and that infiltration and runoff depend in a strong non‐linear way on slope and the properties of MT. Three regimes of influence of MT were identified: one in which MT plays a negligible role but there is a high sensitivity to the infiltration capacity curve, a second regime in which hydrological partitioning is highly sensitive to MT and the infiltration capacity curve, and a third regime in which MT increases infiltration, but the response is insensitive to particular features, and more affected by the average slopes. The regimes are the product of the interplay between small (MT) and large scale (slope) properties. Furthermore, the results suggest that hydrological signatures can be interpreted and explained by the spatiotemporal variation of surface connectivity.
... Redistribution of water towards dense biomass patches drives further plant growth in these regions and thus closes the feedback loop. First discovered through areal photography in the 1950s [52], vegetation patterns have been detected in various semi-arid regions of the world (see [91,28] for reviews) such as in the African Sahel [60,16], Somalia [37,34], Australia [18,46], Israel [75,8], Mexico and the US [16,65,64] and northern Chile [26]. The understanding of the evolution and underlying dynamics of patterned vegetation is of crucial importance as changes to properties such as pattern wavelength, recovery time from perturbations or the area fraction colonised by plants may provide an early indication of an irreversible transition to full desert [44,69,14,33,58,15,73,100]. ...
Patterns of vegetation are a characteristic feature of many semi-arid regions. The limiting resource in these ecosystems is water, which is added to the system through short and intense rainfall events that cause a pulse of biological processes such as plant growth and seed dispersal. We propose an impulsive model based on the Klausmeier reaction–advection–diffusion system, analytically investigate the effects of rainfall intermittency on the onset of patterns, and augment our results by numerical simulations of model extensions. Our investigation focuses on the parameter region in which a transition between uniform and patterned vegetation occurs. Results show that decay-type processes associated with a low frequency of precipitation pulses inhibit the onset of patterns and that under intermittent rainfall regimes, a spatially uniform solution is sustained at lower total precipitation volumes than under continuous rainfall, if plant species are unable to efficiently use low soil moisture levels. Unlike in the classical setting of a reaction–diffusion model, patterns are not caused by a diffusion-driven instability but by a combination of sufficiently long periods of droughts between precipitation pulses and water diffusion. Our results further indicate that the introduction of pulse-type seed dispersal weakens the effects of changes to width and shape of the plant dispersal kernel on the onset of patterns.
... Vegetation patterns are a characteristic feature of such fragile ecosystems. Patterns have been detected in semi-desert regions in the African Sahel [80,91,92,46,17], Somalia [31,29], Australia [21,83,39], Israel [64,10] and Mexico and the US [13,45,44,17,49,48]. Changes to characteristic features of vegetation patterns in these regions such as the pattern wavelength, the area fraction covered by biomass, or the recovery time from perturbations can act as early indicators of desertification as they provide a useful tool in predicting further changes to ecosystems [15,59,55,38,28,14,93]. ...
Vegetation patterns are a ubiquitous feature of water-deprived ecosystems. Despite the competition for the same limiting resource, coexistence of several plant species is commonly observed. We propose a two-species reaction-diffusion model based on the single-species Klausmeier model, to analytically investigate the existence of states in which both species coexist. Ecologically, the study finds that coexistence is supported if there is a small difference in the plant species' average fitness, measured by the ratio of a species' capabilities to convert water into new biomass to its mortality rate. Mathematically, coexistence is not a stable solution of the system, but both spatially uniform and patterned coexistence states occur as metastable states. In this context, a metastable solution in which both species coexist corresponds to a long transient (exceeding $10^3$ years in dimensional parameters) to a stable one-species state. This behaviour is characterised by the small size of a positive eigenvalue which has the same order of magnitude as the average fitness difference between the two species. Two mechanisms causing the occurrence of metastable solutions are established: a spatially uniform unstable equilibrium and a stable one-species pattern which is unstable to the introduction of a competitor. We further discuss effects of asymmetric interspecific competition (e.g. shading) on the metastability property.
... Redistribution of water towards dense biomass patches drives further plant growth in these regions and thus closes the feedback loop. First discovered through areal photography in the 1950s [49], vegetation patterns have been detected in various semi-arid regions of the world (see [83,25] for reviews) such as in the African Sahel [54,16], Somalia [34,31], Australia [17,43], Israel [68,8], Mexico and the US [16,58,57] and northern Chile [23]. The understanding of the evolution and underlying dynamics of patterned vegetation is of crucial importance as changes to properties such as pattern wavelength, recovery time from perturbations or the area fraction colonised by plants may provide an early indication of an irreversible transition to full desert [41,62,14,30,53,15,66,90]. ...
Patterns of vegetation are a characteristic feature of many semi-arid regions. The limiting resource in these ecosystems is water, which is added to the system through short and intense rainfall events that cause a pulse of biological processes such as plant growth and seed dispersal. We propose an impulsive model based on the Klausmeier reaction-advection-diffusion system, analytically investigate the effects of rainfall intermittency on the onset of patterns, and augment our results by numerical simulations of model extensions. Our investigation focuses on the parameter region in which a transition between uniform and patterned vegetation occurs. Results show that decay-type processes associated with a low frequency of precipitation pulses inhibit the onset of patterns and that under intermittent rainfall regimes, a spatially uniform solution is sustained at lower total precipitation volumes than under continuous rainfall, if plant species are unable to efficiently use low soil moisture levels. Unlike in the classical setting of a reaction-diffusion model, patterns are not caused by a diffusion-driven instability but by a combination of sufficiently long periods of droughts between precipitation pulses and water diffusion. Our results further indicate that the introduction of pulse-type seed dispersal weakens the effects of changes to width and shape of the plant dispersal kernel on the onset of patterns.
... When flowing downslope onto typically vegetation-covered slope sections with higher infiltration capacities (i.e., run-on)(e.g., Corradini et al., 1998), flow velocities and transport capacities decrease. This self-stabilizing process is responsible for the generation of banded vegetation patterns and associated landforms in semiarid environments (tiger stripes, brousse tigreé; Dunkerley and Brown, 1999;Valentin et al., 1999;Pelletier et al., 2012;Sherratt, 2015), and may potentially serve as an explanation for the formation of zebra stripes in the Atacama. Given the lack of both vegetation and observable overland flow under modern climatic conditions, active stripe formation due to run-on-runoff processes requires more humid climatic conditions in the past ( Owen et al., 2013). ...
Although a number of studies have pointed out the remarkable slowness of Earth surface processes in the Atacama Desert, process mechanisms under such extremely limited water availability are poorly understood, and process rates remain unknown. This paper revisits the discussion on the formation of the prominent Atacama-specific hillslope zebra (stone) stripes, previously interpreted to result from palaeo-overland flow (Owen et al., 2013). Compared to previous studies, our data document different stripe characteristics with regard to stripe form and orientation as well as sorting- and bedding-patterns of stripe-confining surface gravel units. We found a remarkable form-concordance between zebra stripes and deposits from experiments on segregation-induced granular fingering. Hence, we propose a combination of seismic shaking and instantaneous dry granular free surface flows as the key mechanism for zebra stripe formation. Our findings underline the potential significance of seismicity in shaping Atacama landscapes, which bear important analogies to extra-terrestrial surfaces.
... Cramer & Barger, 2013;Puigdefábregas & Sánchez, 1996). These patterns were first recognized from aerial photographs of Africa (Clos-Arceduc, 1956;Macfadyen, 1950;Worral, 1960), and have later been described for semi-arid areas around the world (Berg & Dunkerley, 2004;Deblauwe, Barbier, Couteron, Lejeune, & Bogaert, 2008;Deblauwe, Couteron, Bogaert, & Barbier, 2012;Moreno-de las Heras, Saco, Willgoose, & Tongway, 2012;Pelletier et al., 2012;Penny, Daniels, & Thompson, 2013). This self-organized patchiness is commonly attributed to the effect of short-ranged facilitation within vegetation patches and long-range competition for resources between patches, constituting an ecohydrological feedback Stewart et al., 2013). ...
... Increased infiltration as a result of the presence of roots, macropores, soil aggregation and absence of crusts; reduced soil evaporation due to the vegetation canopy (Ludwig, Wilcox, Breshears, Tongway, & Imeson, 2005;Pelletier et al., 2012;Puigdefábregas, 2005;Thompson, Katul, & Porporato, 2010;Tongway & Ludwig, 2001;Tongway, Ludwig, & Whitford, 1989) and runon from upslope bare areas (Ludwig et al., 2005;Puigdefabregas, Sole, Gutierrez, del Barrio, & Boer, 1999;Saco, Willgoose, & Hancock, 2007;Valentin, d'Herbès, & Poesen, 1999;Wilcox, Breshears, & Allen, 2003). Within this runoff-runon system, runoff generated in the bare areas (sources) flows towards the vegetated areas (sinks) where it (partly) infiltrates into the soil (Thompson et al., 2010) and (partly) continues to flow downstream into the vegetated area, depending on rainfall amount and timing. ...
... Several studies (Ludwig et al., 2005, and references cited therein) have suggested that differences between patches and interpatches appear to depend on, among other factors, the topography. However, as discussed by Pelletier et al. (2012), the standard conceptual model for vegetation bands includes no explicit role for topography. Moreover, as highlighted by McGrath, Paik, and Hinz (2012), the role that various general topographical settings have in vegetation pattern formation is still an open question; they also stated that both smaller-scale and larger-scale variations in topography are likely to add to the complexity of the ecohydrological feedbacks. ...
Semi‐arid ecosystems are often spatially self‐organized in typical patterns of vegetation bands with high plant cover interspersed with bare soil areas, also known as ‘tiger bush’.
In modelling studies, most often, straight planar slopes were used to analyse vegetation patterning. The effect of slope steepness has been investigated widely, and some studies investigated the effects of microtopography and hillslope orientation. However, at the larger catchment scale, the overall form of the landscape may affect vegetation patterning and these more complex landscapes are much more prevalent than straight slopes. Hence, our objective was to determine the effect of landform variation on vegetation patterning and sediment dynamics. We linked two well‐established models that simulate (a) plant growth, death and dispersal of vegetation, and (b) erosion and sedimentation dynamics. The model was tested on a straight planar hillslope and then applied to (i) a set of simple synthetic topographies with varying curvature and (ii) three more complex, real‐world landscapes of distinct morphology. Results show banded vegetation patterning on all synthetic topographies, always perpendicular to the slope gradient. Interestingly, we also found that movement of bands – a debated phenomenon – seems to be dependent on curvature. Vegetation banding was simulated on the slopes of the alluvial fan and along the valley slopes of the dissected and rolling landscapes. In all landscapes, local valleys developed a full vegetation cover induced by water concentration, which is consistent with observations worldwide. Finally, banded vegetation patterns were found to reduce erosion significantly as compared to other vegetation configurations.
... Instead, most of the water flows down into the next patch of vegetation. The soil in such regions have founded in many parts of the earth including Africa [2,3], Australia [4,5], North America [2,6,7,8], Middle East [9,10] and Asia [11]. Since ecological laboratory setups are very costly and field studies are very hard for data collection due to short duration, mathematical modeling of such systems plays vital role to understanding the mechanisms of semi-arid environments from turning into full-blown deserts. ...
... When the discriminant of (10) is = 0; then 2 = 4 2 , so = 2 . We find that solution is as (8) and = 2 due to (8) and it shows that the equilibrium point is ...
In semi-arid environment, vegetation bands are self-organized into spatial patterns. Particularly, they are typical on hills lie along the gentle slopes. For this phenomenon, we consider a coupled nonlinear reaction-diffusion evolutionary PDE model for banded vegetation pattern in a semi-arid ecosystem. We study Klausmeier model to analyze the zero-dimensional nonlinear ODE system and investigate the qualitative behavior of the parameter-dependent equilibrium of the system as rainfall changes. Using unstable homogeneous steady state, we show parameter plane in which patterns exist and find that the intermediate levels of rainfall is responsible for pattern formation.
... The combination of climate change, population growth, and soil threats including carbon loss, biodiversity decline, and erosion increasingly challenge the global community (Schwilch et al., 2016). A major scientific challenge in understanding processes involved in soil threats, landscape resilience, ecosystem stability, sustainable land management, and the economic consequences is that it is an interdisciplinary field (Pelletier et al., 2012), requiring more openness between scientific disciplines (Liu et al., 2007). As a result of single disciplinary focus, ambiguity arises in the understanding of landscape interactions, especially interactions between biological and physical processes in a landscape (Cook & Hauer, 2007). ...
... Pelletier et al. (2012) assessed coevolution within vegetation dynamics, pedogenesis, and topographic development in southern California using a landscape modelling approach. They found strong correlations between effective energy and mass transfer, above-ground biomass, soil thickness, hillslope-scale relief, and mean distance-to-valley. ...
Landscape composition and land use impact the interactions between soil and vegetation. Differences in micro-behaviour, driven by the interplay of heterogeneous soil and vegetation dynamics, affect emergent characteristics across a landscape. Scaling approaches to understand the drivers of these emergent characteristics have been attempted, but the blueprint of interacting biophysical processes in landscapes is inherently messy and often still unknown. A complicating factor is single disciplinary focus in environmental sciences. Integrated knowledge is vital especially in view of future challenges posed by climate change, population growth and soil threats. In this paper we give examples of biophysical interactions which occur across various temporal and spatial scales and discuss how connectivity can be useful for bridging disciplines and scales to increase our understanding.
