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1.
Soil erosion plays an important role in plant colonization of semi‐arid degraded areas. In this study, we aimed at deepening our knowledge of the mechanisms that control plant colonization on semi‐arid eroded slopes in east Spain by (i) determining topographic thresholds for plant colonization, (ii) identifying the soil properties limiting plant establishment and (iii) assessing whether colonizing species have specific plant traits to cope with these limitations. Slope angle and aspect were surrogates of erosion rate and water availability, respectively. Since soil erosion and water availability can limit plant establishment and both can interact in the landscape, we analysed variations in colonization success (vegetation cover and species number) with slope angle on 156 slopes, as a function of slope aspect. After determining slope angle thresholds for plant colonization, soil was sampled near the threshold values for soil analysis [nitrogen, phosphorous, calcium carbonate (CaCO3), water holding capacity]. Plant traits expressing the plant colonizing capacity were analysed both in the pool of species colonizing the steep slopes just below the threshold and in the pool of species inhabiting gentler slopes and absent from the slopes just below the threshold. Results show that the slope angle threshold for plant colonization decreased from north to south. For the vegetation cover, threshold values were 63°, 50°, 46°, 41° for the north, east, west and south slope aspect classes, respectively, and 65°, 53°, 49° and 45° for the species richness and the same aspect classes. No differences existed in soil properties at slope angle threshold values among slope aspects and between slope positions (just below and above the threshold) within slope aspect classes. This suggests that variations between slope aspect classes in the slope angle threshold result from differences in the colonizing capacity of plants which is controlled by water availability. Long‐distance dispersal and mucilage production were preferably associated with the pool of colonizing species. These results are discussed in the perspective of a more efficient ecological restoration of degraded semi‐arid ecosystems where soil erosion acts as an ecological filter for plant establishment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Badland landscapes exhibit high erosion rates and represent the main source of fine sediments in some catchments. Advances in high-resolution topographic methods allow analysis of topographic changes at high temporal and spatial scales. We apply the Mapping Geomorphic Processes in the Environment (MaGPiE) algorithm to infer the main geomorphic process signatures operating in two sub-humid badlands with contrasting morphometric attributes located in the Southern Pyrenees. By interrogating a 5-year dataset of seasonal and annual topographic changes, we examine the variability of geomorphic processes at multiple temporal scales. The magnitude of geomorphic processes is linked to landform attributes and meteorological variables. Morphometric differences between both adjacent badlands allow us to analyse the role of landform attributes in the main geomorphic process reshaping landscapes subjected to the same external forcing (i.e. rainfall and temperature). The dominant geomorphic process signatures observed in both badlands are different, despite their close proximity and the same rainfall and temperature regimes. Process signatures determining surface lowering in the gently sloping south-facing badland, characterized by lower connectivity and more vegetation cover, are driven by surface runoff-based processes, both diffuse (causing sheet washing) and concentrated (determining cutting and filling, rilling and gullying). The steeper, more connected north-facing slopes of the other badland are reshaped by means of gravitational processes, with mass wasting dominating topographic changes. In terms of processes determining surface raising, both mass wasting and cutting and filling are most frequently observed in both badlands. There is a clear near-balanced feedback between both surface-raising and -lowering processes that becomes unbalanced at larger temporal scales due to the thresholds overcome, as the volume associated with surface lowering becomes higher than that associated with raising-based processes. Rainfall variables control surface flow processes, while those variables associated with low temperature have a significant relation with mass movement-based processes and other localized processes such as regolith cohesion loss. Finally, our results point out that morphometry (slope and connectivity) together with vegetation cover are key factors determining geomorphic processes and associated topographic changes. © 2020 John Wiley & Sons, Ltd.  相似文献   

3.
Gully and badland erosion constitute important land‐degradation processes with severe on‐site and off‐site effects above all in sedimentary deposits and alluvial soils of the arid and semi‐arid regions. Agricultural use of the affected land is impeded both by the irreversible loss of topsoil and the morphological dissection of the terrain. In various badland regions around the world, a solution to the latter problem is attempted by infilling of gullies and levelling of badland topography in order restore a morphology suitable for agricultural cultivation. Gully and badland levelling for agricultural reclamation has been conducted for decades in the large ravine lands of India. This study aims at analysing the distribution and dynamics of land levelling within the Chambal badlands in Morena district, Madhya Pradesh, between 1971 and 2015. Using high to medium resolution satellite images from the Corona, Landsat, Aster and RapidEye missions and a multi‐temporal classification approach, we have mapped and quantified areas that were newly levelled within eight observation periods. We analysed the spatial relation of levelled land to several physical and socio‐economic factors that potentially influence the choice of reclamation site by employing geographic information system (GIS) analysis methods and results from focus‐group discussions in selected villages. Results show that nearly 38 km2 or 23% of the badlands in the study area have been levelled within 45 years. The levelling rate generally increases during the observation period, but the annual variability is high. We have found spatial relationships to badland morphology, vicinity of existing cropland and proximity to villages and drainage lines. From a socio‐economic point of view, availability of financial and technical means, access rights to the badland and ownership issues play an important role. Considering studies on soil degradation caused by levelling of badlands in other regions, the sustainability of the newly reclaimed fields in the Chambal badlands is questionable. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

4.
Agricultural land abandonment is currently widely spread in Mediterranean countries and a further increase is expected. Previous research has shown that abandoned fields in semi‐arid areas are more vulnerable to gully erosion. The absence of ploughing and slow vegetation recovery cause the formation of soil crusts with low infiltration rates, resulting in increased runoff and gully erosion risk. The objective of our study was to assess the extent and causes of erosion and terrace failure on abandoned fields and to discuss options for mitigation. The study was carried out in the Carcavo basin, a semi‐arid catchment in southeast Spain. At catchment scale all abandoned fields were surveyed and characteristics of each field were described. Additionally we surveyed abandoned and cultivated terraces and used statistical analyses to determine the factors that induce terrace failure. At field scale we constructed a detailed digital elevation model (DEM) for an abandoned terrace field in order to calculate sediment losses since time of abandonment. The results revealed that more than half the abandoned fields had moderate to severe erosion and the statistical analysis showed that these fields had significantly steeper slopes, were terraced and had cereals as previous land use. Factors that increase the risk of terrace failure were land abandonment, steeper terrace slope, loam texture, valley‐bottom position and shrubs on the terrace wall. The reconstructed erosion rate (87 ton ha?1 year?1) confirmed the importance of gully erosion on these abandoned terrace fields. Potential soil and water conservation practices to mitigate soil erosion after abandonment are: (1) maintenance of terrace walls, as a result more water is retained, which increases vegetation cover and consequently decreases erosion. (2) Revegetation with indigenous grass species on spots with concentrated flow, especially near terrace walls. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
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6.
Many studies attribute the effects of vegetation in reducing soil erosion rates to the effects of the above‐ground biomass. The effects of roots on topsoil resistance against concentrated flow erosion are much less studied. However, in a Mediterranean context, where the above‐ground biomass can temporarily disappear because of fire, drought or overgrazing, and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on Mediterranean plant characteristics, especially root characteristics, growing on semi‐natural lands, and knowledge of their suitability for gully erosion control is often lacking. A methodological framework to evaluate plant traits for this purpose is absent as well. This paper presents a methodology to assess the suitability of plants for rill and gully erosion control and its application to 25 plant species, representative for a semi‐arid Mediterranean landscape in southeast Spain. In this analysis determination of suitable plants for controlling concentrated flow erosion is based on a multi‐criteria analysis. First, four main criteria were determined, i.e. (1) the potential of plants to prevent incision by concentrated flow erosion, (2) the potential of plants to improve slope stability, (3) the resistance of plants to bending by water flow and (4) the ability of plants to trap sediments and organic debris. Then, an indicator or a combination of two indicators was used to assess the scores for the four criteria. In total, five indicators were selected, i.e. additional root cohesion, plant stiffness, stem density, the erosion‐reducing potential during concentrated flow and the sediment and organic debris obstruction potential. Both above‐ and below‐ground plant traits were taken into account and measured to assess the scores for the five indicators, i.e. stem density, sediment and organic debris obstruction potential, modulus of elasticity of the stems, moment of inertia of the stems, root density, root diameter distribution, root area ratio and root tensile strength. The scores for the indicators were represented on amoeba diagrams, indicating the beneficial and the weak plant traits, regarding to erosion control. The grasses Stipa tenacissima L. and Lygeum spartum L. and the shrub Salsola genistoides Juss. Ex Poir. amongst others, were selected as very suitable plant species for rill and gully erosion control. Stipa tenacissima can be used to re‐vegetate abandoned terraces as this species is adapted to drought and offers a good protection to concentrated flow erosion and shallow mass movements. Lygeum spartum can be used to vegetate concentrated flow zones or to obstruct sediment inflow to channels at gully outlets. Stipa tenacissima and Salsola genistoides can be used to stabilize steep south‐facing slopes. The methodology developed in this study can be applied to other plant species in areas suffering from rill and gully erosion. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
In the Mediterranean region, semi‐natural shrubland communities (named ‘matorral’) often present a discontinuous cover, where isolated perennial plants alternate with bare inter‐plant areas. In such ecosystems, the patchy distribution of the vegetation is usually associated with microtopographic sequences of mounds that develop under isolated plants and break the overall slope continuity. In this study, the influence of three representative species of the Mediterranean matorral (Rosmarinus officinalis, Stipa tenacissima and Anthyllis cytisoides) on slope microtopography is determined and the processes that take part in the development of microtopographic structures beneath the plant canopy are identified. The influence of slope gradient, plant species and plant parameters on the shape and height of microtopographic structures is also studied. The shape of the microtopographic structures is described by using a two‐dimensional microprofilemeter and mound height is determined by measuring in the field a ‘mound height index’ defined as the distance from the top to the bottom of the mound. The results obtained show that plant species play a major role in the shape and height of the microtopographic structures. Whereas terrace‐type structures generally develop under Anthyllis shrubs, microtopographic forms associated with Rosmarinus and Stipa plants vary with slope gradient. The almost symmetric mound‐type structures that develop under these two species on gentle slopes change into terrace‐type structures as slope gradient increases. Moreover, statistically significant differences exist between the three species with regard to mound height. Mean values of mound height are 19·4, 14·6 and 4·3 cm under the canopy of Stipa, Rosmarinus and Anthyllis respectively. Plant parameters, essentially roughness, and slope gradient have a significant influence on mound height index. Four main processes were identified as affecting mound development in the studied field site: sedimentation, differential interrill erosion, differential splash erosion and bioturbation. Plant species interact in different ways with these processes according to their morphologies. Since Stipa and Rosmarinus plants are more efficient than Anthyllis shrubs in controlling water erosion, in retaining sediments and in modifying soil properties under their respective canopies, they give rise to higher microtopographic structures that facilitate water and nutrient storage by plants on slopes. Copyright © 2000 John Wiley & Sons, Ltd  相似文献   

8.
Climate change is expected to increase temperatures and lower rainfall in Mediterranean regions; however, there is a great degree of uncertainty as to the amount of change. This limits the prediction capacity of models to quantify impacts on water resources, vegetation productivity and erosion. This work circumvents this problem by analysing the sensitivity of these variables to varying degrees of temperature change (increased by up to 6·4 °C), rainfall (reduced by up to 40%) and atmospheric CO2 concentrations (increased by up to 100%). The SWAT watershed model was applied to 18 large watersheds in two contrasting regions of Portugal, one humid and one semi‐arid; incremental changes to climate variables were simulated using a stochastic weather generator. The main results indicate that water runoff, particularly subsurface runoff, is highly sensitive to these climate change trends (down by 80%). The biomass growth of most species showed a declining trend (wheat down by 40%), due to the negative impacts of increasing temperatures, dampened by higher CO2 concentrations. Mediterranean species, however, showed a positive response to milder degrees of climate change. Changes to erosion depended on the interactions between the decline in surface runoff (driving erosion rates downward) and biomass growth (driving erosion rates upward). For the milder rainfall changes, soil erosion showed a significant increasing trend in wheat fields (up to 150% in the humid watersheds), well above the recovery capacity of the soil. Overall, the results indicate a shift of the humid watersheds to acquire semi‐arid characteristics, such as more irregular river flows and increasingly marginal conditions for agricultural production. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

9.
Four areas were selected to represent a range of processes characteristic of badland surfaces in southeast Spain: Petrer and Monnegre in Alicante, Vera and Tabernas in Almería. At Petrer, rilling and swelling processes produce a deeply cracked surface drained by a finely textured network of shallow rills. At Monnegre, piping and rilling are differentially developed on slopes ultimately controlled by basal incision. At Vera, aspect-controlled lichen and vegetation cover produce a sequence of badland development within which the relative importance of piping, mass movement and rilling varies through the sequence. At Tabernas, simple overland flow is the dominant process, but aspect influences rill network density and badland evolution. The factors controlling badland development can be grouped into those related to gross morphology, to surface cover and runoff generation, and to material properties. These factors are effective over varying timescales, implying that morphological response times differ among the selected badlands.  相似文献   

10.
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. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

11.
Denudation mechanisms differ fundamentally between limestone and silicate rock types, which are subject to very different rate thresholds and enhancers/inhibitors. Silicates are removed largely by erosion, the mechanical entrainment and transport of particles. This is a relatively high energy, and highly episodic, process which occurs only when a minimum threshold ?ow velocity is exceeded; it is inhibited by vegetation cover and favoured by strongly seasonal runoff. Limestone is removed largely by chemical dissolution at a rate directly proportional to runoff. Dissolution is a relatively low energy process that can occur at any ?ow velocity or in static water; in general it is enhanced by vegetation cover and non‐seasonality of runoff. These contrasting factors in the denudation of silicates versus limestone can produce strikingly uneven rates of surface lowering across a landscape, sometimes akin to the well known ‘tortoise and hare race’, where the slow and steady denudation of limestones may in the long term exceed the sometimes rapid, but often localized and episodic, erosion of silicates. Prolonged exposure of limestone to a humid temperate climate in a tectonically stable environment produces low‐relief corrosion plains in which limestone uplands are anomalous and, in most instances, due to recent unroo?ng from beneath a siliciclastic cover. In a highly seasonal or semi‐arid climate almost the exact inverse may develop, with ‘?ashy’ runoff and sparse vegetation favouring erosion rather than dissolution. Even under a constant humid climate progressive unroo?ng of a thick limestone unit within folded siliciclastics may lead to a topographic inversion over time, with the limestone outcrop always forming a topographic low ?anked by siliciclastic uplands. Valleys will be initiated on anticlinal crests, where the limestone is ?rst unroofed, but progressive lowering of the limestone causes these valleys to migrate to their ?nal position in the synclinal troughs. In humid climates isostatic compensation in response to slow, but continuous, denudation of extensive limestone outcrops may be a signi?cant factor in the development of relief on adjacent, more slowly eroding, silicate outcrops. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

12.
Talus flatirons are debris‐covered relict slopes, disconnected from the source area, which are relatively common in arid and semi‐arid areas. Talus flatiron sequences record the alternation of accumulation and incision phases. These chronosequences may be used for infer temporal changes in the morphogenetic processes acting on the slopes as well as information on the local paleoclimatic history. Talus flatiron sequences developed in the Tremp Depression, eastern Spanish Pyrenees, are analysed from the geomorphological, chronological and paleoenvironmental perspective. The two groups of relict slopes differentiated by means of detailed geomorphological mapping have been dated by optically stimulated luminescence (OSL) and radiocarbon dating at 25–20 kyr (S3) and 5·4–1·7 cal kyr (S2). The talus flatiron group S3 is correlated with a fluvial terrace of the Noguera Pallaresa River (c. 23 kyr bp ). The comparison of the ages obtained in the Tremp Depression with chronologies published for talus flatiron sequences in semi‐arid areas and other paleoclimatic proxies suggests that the aggradation phases in the slopes occurred during periods with higher humidity and vegetation cover. The chronological differences observed between semi‐arid Spain and the Tremp Depression may be partly related to the more humid climate of the latter mountain area. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

13.
Badland areas provide some of the highest erosion rates globally. Most studies of erosion have insufficient lengths of record to interrogate the impacts of decadal‐scale changes in precipitation on rates of badland erosion in regions such as the Mediterranean, which are known to be sensitive to land degradation and desertification. Erosion measurements, derived from field monitoring using erosion pins, in southern Italy during the period 1974–2004 are used to explore the impacts of changing precipitation patterns on badland erosion. Erosion on badland inter‐rill areas is strongly correlated with cumulative rainfall over each monitoring period. Annual precipitation has a substantial dynamic range, but both annual and winter (December, January, February) rainfall amounts in southern Italy show a steady decrease over the period 1970–2000. The persistence of positive values of the winter North Atlantic Oscillation index in the period 1980–2000 is correlated with a reduction in the winter rainfall amounts. Future climate scenarios show a reduction in annual rainfall across the western and central Mediterranean which is likely to result in a further reduction in erosion rates in existing badlands. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
Present erosion in mountainous areas of Western Europe causes land management problems, particularly for areas located downstream of erosion zones. Except for transalpine roads and ski resorts, economic activities no longer require as much space as they did in the past. Therefore, natural reforestation has provided signi?cant protection for alpine hillslopes during the 20th century. However, extreme ?oods continue to cause severe damage in intra‐alpine valleys, as well as in piedmont and surrounding plains, making the study of present water erosion phenomena very important. Many studies have investigated the processes and factors of water erosion on slopes at both the catchment and plot scales. They have focused on rock fragmentation and transportation in different ?elds, the spatial and temporal explanatory variables, the consequences downstream (?ooding, sedimentation, river bed evolution) and the impact of ?oods. In the French Alps, present erosion has been studied in a variety of outcrops, with several recent studies conducted in ?elds such as marls, clayey deposits, molasses and moraines. These kinds of outcrops are found throughout the alpine massif, including an area of special interest on the great Jurassic black marl outcrop where badlands are frequently observable. Geomorphologists and hydrologists have been particularly interested in the strong erosion processes in marls, seeking to determine the main patterns and the impact of spatial and temporal factors on soil loss quantities. The main climatic factors of rock disaggregation were found to be the freeze–thaw and wet–dry cycles, which destroy rock cohesion, and the splash effect of rain. The principal site variables are vegetation cover, exposure and dip–slope angle. Erosion rates are two or three orders of magnitude higher on bare soils than on pastures; northern aspect slopes suffer two to four times as much soil loss as southern aspect slopes. Finally, the angle formed by the slope and the dip also determines different behaviours: erosion rates are higher when slope and dip are perpendicular than when they are parallel. The transportation agents are mostly debris ?ows and runoff caused by intense precipitation. Annual erosion depth in the marls is generally assumed to be substantial, up to 10 mm. The high value can be explained by the severity of the climatic conditions and the brittleness of the lithology, which results in numerous fractures. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

15.
Connectivity has recently emerged as a key concept for understanding hydrological response to vegetation change in semi‐arid environments, providing an explanatory link between abiotic and biotic, structure and function. Reduced vegetation cover following woody encroachment, generally promotes longer, more connected overland flow pathways, which has the potential to result in an accentuated rainfall‐runoff response and fluxes of both soil erosion and carbon. This paper investigates changing hydrological connectivity as an emergent property of changing ecosystem structure over two contrasting semi‐arid grass to woody vegetation transitions in New Mexico, USA. Vegetation structure is quantified to evaluate if it can be used to explain observed variations in water, sediment and carbon fluxes. Hydrological connectivity is quantified using a flow length metric, combining topographic and vegetation cover data. Results demonstrate that the two woody‐dominated sites have significantly longer mean flowpath lengths (4 · 3 m), than the grass‐dominated sites (2 · 4 m). Mean flowpath lengths illustrate a significant positive relationship with the functional response. The woody‐dominated sites lost more water, soil and carbon than their grassland counterparts. Woody sites erode more, with mean event‐based sediment yields of 1203 g, compared to 295 g from grasslands. In addition, the woody sites lost more organic carbon, with mean event yields of 39 g compared to 5 g from grassland sites. Finally, hydrological connectivity (expressed as mean flowpath length) is discussed as a meaningful measure of the interaction between structure and function and how this manifests under the extreme rainfall that occurs in semi‐arid deserts. In combination with rainfall characteristics, connectivity emerges as a useful tool to explain the impact of vegetation change on water, soil and carbon losses across semi‐arid environments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Erosion rates and processes define how mountainous landscapes evolve. This study determines the range of erosion rates in a semi‐arid landscape over decadal time spans and defines the dominant processes controlling variability in erosion rates. The varying topography and climatic regimes of the Xiying Basin (Qilian Shan Mountains, China) enables us to examine the relative roles of sheet wash versus rainsplash and the influence of vegetation on soil erosion and deposition. Soil erosion rates since 1954 were determined using 137Cs along 21 transects at four sites with varying gradient, rainfall, and vegetation cover. The mean 137Cs derived soil erosion rate ~0.42 mm/a was consistent with the catchment level erosion rate derived from total sediment yield for a 44 year record. However, there is considerable variability in 137Cs erosion rates both between transects and along transects, perhaps reflecting variation not only in the effectiveness of individual processes but also in their relative roles. We compare the 137Cs‐derived erosion rates with 1‐D models for sediment flux that incorporate sheet wash and rainsplash processes, testing them over a previously untested 60 year timescale. The variability in 137Cs erosion rates along transects is best replicated by sheet wash dominated simulations, suggesting that this is the dominant erosion process in this semi‐arid landscape. The functional form of the sheetwash model can also explain our observations that 137Cs erosion rates decrease with upslope length (i.e. distance down slope) while its variability increases. However, sparsely vegetated sites, located in slightly drier locations, have higher erosion rates, and are not as accurately modeled as densely vegetated sites, suggesting that patchiness of vegetation introduces fine scale variability in erosion rates on these slopes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
Infrequent, high‐magnitude events cause a disproportionate amount of sediment transport on steep hillslopes, but few quantitative data are available that capture these processes. Here we study the influence of wildfire and hillslope aspect on soil erosion in Fourmile Canyon, Colorado. This region experienced the Fourmile Fire of 2010, strong summer convective storms in 2011 and 2012, and extreme flooding in September 2013. We sampled soils shortly after these events and use fallout radionuclides to trace erosion on polar‐ and equatorial‐facing burned slopes and on a polar‐facing unburned slope. Because these radionuclides are concentrated in the upper decimeter of soil, soil inventories are sensitive to erosion by surface runoff. The polar‐facing burned slope had significantly lower cesium‐137 (137Cs) and lead‐210 (210Pb) inventories (p < 0.05) than either the polar‐facing unburned slope or equatorial‐facing burned slope. Local slope magnitude does not appear to control the erosional response to wildfire, as relatively gently sloping (~20%) polar‐facing positions were severely eroded in the most intensively burned area. Field evidence and soil profile analyses indicate up to 4 cm of local soil erosion on the polar‐facing burned slope, but radionuclide mass balance indicates that much of this was trapped nearby. Using a 137Cs‐based erosion model, we find that the burned polar‐facing slope had a net mean sediment loss of 2 mm (~1 kg m?2) over a one to three year period, which is one to two orders of magnitude higher than longer‐term erosion rates reported for this region. In this part of the Colorado Front Range, strong hillslope asymmetry controls soil moisture and vegetation; polar‐facing slopes support significantly denser pine and fir stands, which fuels more intense wildfires. We conclude that polar‐facing slopes experience the most severe surface erosion following wildfires in this region, indicating that landscape‐scale aridity can control the geomorphic response of hillslopes to wildfires. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

18.
A drainage basin simulation model is used to interpret the morphometry and historical evolution of Mancos Shale badlands in Utah. High relief slopes in these badlands feature narrow divides and linear profiles due to threshold mass-wasting. Threshold slopes become longer in proportion to erosion rate, implying lower drainage density and higher relief. By contrast, in slowly eroding areas of low relief, both model results and observations indicate that drainage density increases with relief, suggesting control by critical shear stress. Field relationships and simulation modelling indicate that the badlands have resulted from rapid downcutting of the master drainage below an Early Wisconsin terrace to the present river level, followed by base level stability. As a result, Early Wisconsin alluvial surfaces on the shale have been dissected up to 62 m into steep badlands, and a Holocene alluvial surface is gradually replacing the badland slopes which are erocing by parallel retreat. © 1997 by John Wiley & Sons, Ltd.  相似文献   

19.
Predicting the location of gully heads in various environments is an important step towards predicting gully erosion rates. So far, field data collection and modelling of topographic thresholds for gully head development has mainly focused on gullies that formed in forested areas, rangelands, pastures and cropland. Such information for gullies in badlands however is very scarce. Therefore, this paper aims to extend the database on gully head topographical thresholds through data collection in a badland area and to improve the prediction of gully heads forming at sites with a very low erosion resistance value. For this, we chose a badland site located in central Italy that is characterized by biancana forms and both active and dormant gullies. The definition of the conditions under which present‐day gully heads developed allowed a better modelling of the gully head threshold equation, with modification of a previous model and the exemplification of how to use the updated model. The model shows that the resistance to gully head retreat depends on slope gradient and drainage area at gully heads, land use at the moment of gully development (as numerically expressed using parameters derived from the Runoff Curve Number method), surface rock fragment cover, presence of joints, pipes, and factors/processes affecting detachment rate. This study attempted to better understand environmental conditions that control the development of gully heads in badlands through a combination of field data collection of gully heads, an analysis of land use changes over 10 centuries, focusing on the period 1820–2005, and land use management through repeat photography and a critical examination of historical documents. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

20.
Soil‐mantled pole‐facing hillslopes on Earth tend to be steeper, wetter, and have more vegetation cover compared with adjacent equator‐facing hillslopes. These and other slope aspect controls are often the consequence of feedbacks among hydrologic, ecologic, pedogenic, and geomorphic processes triggered by spatial variations in mean annual insolation. In this paper we review the state of knowledge on slope aspect controls of Critical Zone (CZ) processes using the latitudinal and elevational dependence of topographic asymmetry as a motivating observation. At relatively low latitudes and elevations, pole‐facing hillslopes tend to be steeper. At higher latitudes and elevations this pattern reverses. We reproduce this pattern using an empirical model based on parsimonious functions of latitude, an aridity index, mean‐annual temperature, and slope gradient. Using this empirical model and the literature as guides, we present a conceptual model for the slope‐aspect‐driven CZ feedbacks that generate asymmetry in water‐limited and temperature‐limited end‐member cases. In this conceptual model the dominant factor driving slope aspect differences at relatively low latitudes and elevations is the difference in mean‐annual soil moisture. The dominant factor at higher latitudes and elevations is temperature limitation on vegetation growth. In water‐limited cases, we propose that higher mean‐annual soil moisture on pole‐facing hillslopes drives higher soil production rates, higher water storage potential, more vegetation cover, faster dust deposition, and lower erosional efficiency in a positive feedback. At higher latitudes and elevations, pole‐facing hillslopes tend to have less vegetation cover, greater erosional efficiency, and gentler slopes, thus reversing the pattern of asymmetry found at lower latitudes and elevations. Our conceptual model emphasizes the linkages among short‐ and long‐timescale processes and across CZ sub‐disciplines; it also points to opportunities to further understand how CZ processes interact. We also demonstrate the importance of paleoclimatic conditions and non‐climatic factors in influencing slope aspect variations. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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