Article

Geomorphological and Geoecological Controls and Processes Following Gully Development in Alpine Mires, Lesotho

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Abstract

Despite the international reputation of Lesotho's severely eroded landscape, there have been no previous quantitative accounts of soil erosion processes and associated consequences from the alpine belt. This paper examines sedimentological, geomorphological, and geoecological controls and processes following gully development within alpine mires in eastern Lesotho. Contemporary gully extension is controlled by exposure to various sedimentary sequences, by gully sidewall crack development, and by topographic aspect. Significant vertical gully denudation rates of 8 cm (mineral sediment) to 13 cm (peat) were recorded over an 18-mo period. During a 5-d field experiment in July 1999, the continuously frozen south-facing gully walls recorded considerable horizontal movement of peat blocks (avg. = 19.8 mm/5 d), whereas needle ice-induced horizontal particle movement rates on north-facing walls averaged 10.2 mm/5 d. Soil moisture transect data show a pronounced reduction in surface soil moisture toward and between the gullied areas of a mire. The percentage of moisture loss toward midwinter was found to be greater between the gullies (47.4%) than in the adjoining zones, where moisture loss averaged 33.6%. Similarly, vegetation transects indicate a reduction in vegetation cover at the drier and more intensely burrowed (by Otomys, or "ice rats") zones close to the gullies. Invasive dwarf Karroid shrubs (e.g., Chrysocoma ciliata) are now establishing themselves alongside gullies, burrowed sites, and fringe areas of mires. We found that dryland plant invasions around grazing posts and heavily grazed areas on the slopes subsequently spread along alpine hydrological systems, particularly where gully erosion has created a suitable habitat.

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... Approximately, half of the lowlands zone has been cultivated (Pomela et al., 2000), and an additional part has come under urbanisation, meaning that wetlands in this zone have generally lost much of their natural vegetation cover. Thus, the role of wetlands in the delivery of regulating ES, such as sediment trapping, erosion control and flood attenuation is critical in the lowlands, a zone that is highly susceptible to erosion because of dispersive soils and is characterised by a severely eroded landscape (Grab & Deschamps, 2004). The regulating services (phosphate trapping, toxicant removal, nitrate removal, sediment trapping and flood attenuation), which scored highest in the less steep lower-altitude valley-bottom wetlands were also positively correlated. ...
... This is mainly because Lesotho is characterised by high levels of poverty and the majority of the people are highly dependent on subsistence agriculture for livelihoods (Government of Lesotho, 2014). Wetlands are also considered a critical grazing resource for communal livestock in Lesotho (Du Preez & Brown, 2011) and much of the grazing in the mountains takes place within wetlands, which support the most palatable vegetation (Grab & Deschamps, 2004). Wetlands have been reported to provide the best grazing in the landscape and also double the carrying capacity of grasslands (Lannas & Turpie, 2009). ...
... The level of threat was assessed using the WET-EcoServices (Kotze et al., 2007). system (Grab & Deschamps, 2004) and promote encroachment by terrestrial vegetation. Furthermore, a substantial number of alien plant species have also been recorded in these wetlands and some occur quite frequently, while others are dominant in the communities in which they occur (Chatanga & Sieben, 2019). ...
... This includes the north-facing valley-heads of the Sekhokong Range, 3.5 km south-west of the Sani Top border post (Fig. 1), with initial debates focusing on their slope origins (Marker and Whittington, 1971;Marker, 1994;Grab and Hall, 1996). More recently, the site has been the focus of analyses on environmental features responsible for gully development (Grab and Deschamps, 2004). Most notably, the site has been investigated to develop palaeoenvironmental reconstructions based on variable sedimentary sequences exposed along relatively deep wetland gullies (Marker, 1994(Marker, , 1995(Marker, , 1998. ...
... 0 E. The north-facing slope of the Sekhokong Range has at least four valley heads eroded into it, separated by basaltic ridges located just south of its highest point at Hodgson's Peaks (Marker, 1994). The valley heads are approximately 800 m wide and 1200 m deep, each with a tributary stream flowing into a wetland at the foot of the slope (Marker and Whittington, 1971;Marker, 1994;Grab and Deschamps, 2004). The sampling site (Fig. 2) is a gully side-wall formed by one such stream (Marker, 1994: hollow C), which provided an exposed sedimentary sequence of more than 5 m depth (Fig. 3), with alternating colluvial and peat layers (Marker, 1994;Grab and Deschamps, 2004). ...
... The valley heads are approximately 800 m wide and 1200 m deep, each with a tributary stream flowing into a wetland at the foot of the slope (Marker and Whittington, 1971;Marker, 1994;Grab and Deschamps, 2004). The sampling site (Fig. 2) is a gully side-wall formed by one such stream (Marker, 1994: hollow C), which provided an exposed sedimentary sequence of more than 5 m depth (Fig. 3), with alternating colluvial and peat layers (Marker, 1994;Grab and Deschamps, 2004). ...
Article
The eastern Lesotho Highlands host an array of periglacial and glacial geomorphic features. Their analysis has provided past climate interpretations predominantly for cold periods, yet no multi-proxy temporally continuous palaeoenvironmental records exist. This study presents a palaeoenvironmental reconstruction based on sedimentary characteristics, fossil pollen and diatoms from an alpine wetland located in the Sekhokong Mountain Range. The record commences in the late Pleistocene with a wet period from ?16?450 to 14?440 cal a BP, interrupted by dry conditions from ?16?350 to 15?870?cal a BP. From ?14 150 to 8560 cal a BP, drier conditions are inferred, slowly transitioning to warmer, wetter conditions. Warmer, dry conditions are inferred for ?8560?7430?cal a BP, followed by cold, wet conditions from ?7280 to 6560?cal a BP. A dry, warmer period occurs from ?6560 to 3640?cal a BP indicated by pollen, diatom and sedimentary records, followed by cool, wet conditions from ?3400 to 1200?cal a BP. The period from ?1110?cal a BP to the present is characterized by progressive drying. Pronounced cold events are detected from the diatom record. Moisture records appear relatively specific to the topographic setting of Sekhokong near the Great Escarpment edge, probably driven by orographically constrained synoptic controls.
... Lesotho falls entirely within the catchment of this river system (ORASECOM 2015) and the country is drained by the river and its tributaries. Moreover, the high-altitude wetlands of Lesotho are critical in maintaining the water levels not only in dams supporting the Lesotho Highlands Water Project (LHWP), which transfers water to South Africa (Grab & Deschamps 2004), but also in those supplying the local population. Directly and indirectly, wetlands in Lesotho are estimated to contribute about 22% of the country's gross domestic products (GDPs) and 30% of the total employment in the country (Department of Environment 2014). ...
... The earliest studies on the palustrine wetlands of Lesotho were carried out in the early 1960s and 1970s (Guillarmod 1962;Van Zinderen Bakker & Werger 1974). Since then, other studies conducted in the country (Du Preez & Brown 2011; Grab & Deschamps 2004;Meakins & Duckett 1993) were mainly carried out on small areas, focusing on specific or a few wetlands. The current study has provided the most recent and more comprehensive assessment of the palustrine wetlands in the country by providing a classification and description of the wetland vegetation. ...
... The wetlands of Lesotho are a critical resource for livestock grazing, especially in summer when thousands of cattle, sheep and goats are seen grazing on these sensitive ecosystems (Du Preez & Brown 2011;Van Zinderen Bakker & Werger 1974). In fact, much of the grazing in the mountains of Lesotho takes place within wetlands because they harbour the most palatable vegetation (Grab & Deschamps 2004). The Basotho are now sometimes observed keeping their livestock in the mountains throughout the year. ...
Article
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The description and classification of wetland vegetation is important for water resource management and biodiversity conservation as it provides an understanding of the wetland vegetation–environment relationships and information to interpret spatial variation in plant communities. This study discusses the vegetation of the palustrine wetlands of Lesotho based on a phytosociological approach. Data on vegetation and various environmental variables were collected using the Braun-Blanquet method and a standardised protocol developed for environmental information of wetlands in South Africa. The data were analysed mainly by clustering and ordination techniques. Twenty-two communities were found by the classification of the wetland vegetation. These communities were found to be diverse in terms of species richness. The ordination revealed that the wetland vegetation is mainly influenced by altitude, longitude, slope, soil parent material, landscape, inundation, potassium content, soil texture, total organic carbon, nitrogen, electrical conductivity and latitude. Regarding species composition and diversity, plant communities in the Highlands were more diverse and were distinctively different from those in the Lowlands. High-altitude communities were also found to be dominated mainly by C3 plants, while those at low altitudes exhibited the dominance of C4 species. Some communities were either restricted to the Highlands or Lowlands but others exhibited a wide ecological amplitude and occurred over an extensive altitudinal range. The diversity of most of the wetlands, coupled with their restricted habitat, distribution at high altitudes and their role in supplying ecosystem services that include water resources, highlights the high conservation value associated with these wetlands, particularly in the face of climate change and loss of biodiversity. Conservation implications: The study can be invaluable to wetland scientists, managers, biodiversity conservationists, water resource managers and planners and vegetation ecologists in Southern Africa. About 70% of Lesotho falls in the Maloti-Drakensberg, accounting for about 60% of the region, and this makes the study important in biodiversity conservation planning, particularly in the Highlands. The wetlands in Lesotho face severe anthropogenic pressures that include overgrazing and economic development. Given that the Lesotho Highlands as a water catchment is not only important for Lesotho, but also for South Africa and Namibia, the conservation of the associated wetlands and this critical water resource is indispensable.
... The protection of large proportions of endemic species, and the environmental stressors to native species through topography and climate, both heighten the potential damage that invasive species could cause. Chrysocoma ciliata, a drought resistant perennial shrub species, is the subject of conservation management concern in the eastern Lesotho Highlands, as it is believed to be an invasive derived from the Karoo region located at considerably lower altitude and some 400 km to the southwest (Van Zinderen Bakker 1981; Grab and Nüsser 2001;Nüsser and Grab 2002;Grab and Deschamps 2004). This study presents palynological evidence for the intermittent presence of Chryscocoma sp. ...
... Pooley 1998), and 'Sehlahala' (Morris et al. 1993); it has been confirmed that all four terms refer to the same species (cf. Grab and Deschamps 2004). Chrysocoma ciliata is insect pollinated, but due to the small size of the pollen grains, the pollen rain is easily distributed by wind (Mayer et al. 2006). ...
... Chrysocoma ciliata is insect pollinated, but due to the small size of the pollen grains, the pollen rain is easily distributed by wind (Mayer et al. 2006). In the contemporary landscape of eastern Lesotho, these shrubs colonise over-grazed areas with an otherwise degraded land surface (Fig. 1b;Grab and Deschamps 2004;Grundling et al. 2015;Kopij 2015), and are abundant in the immediate area surrounding abandoned cattle posts ( Fig. 1a; Morris et al. 1989) and along intensively used sheep and cattle tracks. It is for this reason that it is widely assumed that the species was introduced into the region at the onset of extensive cattle grazing some *100 years ago (Van Zinderen Bakker 1955;Killick 1978;Grab and Deschamps 2004;Grundling et al. 2015). ...
Article
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Over recent decades, concern has been raised regarding the management of Chrysocoma ciliata L. (Asteraceae syn. C. tenuifolia) in the eastern Lesotho Highlands. This shrub species is argued to be a Karroid invasive introduced anthropogenically within the last century. Historical botanical records in Lesotho are scarce, so the origins of this species in the region are as yet uncertain. Speculation is based on the contemporary abundance of these shrubs in overgrazed areas throughout the highlands. This study presents fossil pollen records for the eastern Lesotho Highlands which confirm the presence of this species intermittently throughout the past ~6000 cal yr BP. In so doing, this study refutes claims that the species was introduced anthropogenically within the past 100 years, and of its narrow definition as a Karoo species invasive in Lesotho. The intermittent appearance of this species in the pollen record, however, indicates that it is climate sensitive, colonising the wetlands under conditions unsuitable to other plant species. Evidence presented here calls for a re-evaluation of the categorisation of C. ciliata as an invasive in the Lesotho Highlands, and more critically, for a redevelopment of the environmental management policies which involve this species.
... There have been reports of demographic changes in ice rats, inferred from the high rates of vegetation loss and thus soil erosion in the Drakensberg (e.g. Grab & Deschamps 2004), which may be a response to environmental warming, as can be seen from the increase in minimum temperatures over the past decade or so (data from the Lesotho Weather Services 2005; Fig. 1). This could be a natural consequence of better overwinter survival. ...
... Temperatures range from a mean of 6°C (absolute minimum of -13°C) in winter to 12°C (absolute maximum of 22°C) in summer. Summers are rainy whereas winters are cold and dry accompanied by regular snowfall (Grab & Deschamps 2004). Mean annual precipitation exceeds 1200 mm (Grab & Deschamps 2004). ...
... Summers are rainy whereas winters are cold and dry accompanied by regular snowfall (Grab & Deschamps 2004). Mean annual precipitation exceeds 1200 mm (Grab & Deschamps 2004). The three localities were selected for study because they have naturally occurring ice rat colonies that have been previously studied (Willan 1990;Hinze 2005;Schwaibold 2005) and for their accessibility to researchers. ...
Article
Increasing environmental temperatures may lead to better survival of organisms that are usually susceptible to low temperatures. We investigated whether the numbers of the ice rat Otomys sloggetti robertsi, whose populations are regulated by low temperatures, have increased in the recent past as a consequence of current environmental warming in the Lesotho Drakensberg. Ice rats are endemic to the southern African alpine zone, are exclusively herbivorous, have a diurnal activity profile, and live in underground burrows. We predicted that ice rat numbers would remain stable or increase since winters have become milder. We monitored ice rat numbers in three locations, separated by 70, 80 and 130 km. The results show that the population density of ice rats has increased over threefold to 352 ice rats per hectare over the past decade. Our findings suggest that higher temperatures could have improved habitat productivity and reduced thermal stress, and thus improved winter survival of ice rats.
... Moreover, little is known about non-anthropogenic influences on soil erosion, particularly the contribution made by the ice rat Otomys sloggetti robertsi. Nonetheless, the local human inhabitants in Lesotho have raised concerns about the damage to their pastures caused by ice rats (Mokotjomela, 2007), and Grab and Deschamps (2004) have implicated ice rats in soil erosion because of their overgrazing and burrowing activities, which they associate with increasing ice rat population densities, as reviewed by Mokotjomela (2007). ...
... Summers are mild (mean of 12 C and absolute maximum of 22 C) and wet, whereas winters are cold (mean of 6 C and an absolute minimum of À13 C) and dry and characterised by regular snowfall (Grab, 1997). Mean annual precipitation exceeds 1200 mm (Grab and Deschamps, 2004). The alpine vegetation in this area is characterised by woody species such as Erica sp. and Helichrysum sp. and grasslands dominated by Festuca sp., Danthonia sp. and Pentaschistis sp. ...
... An important contributor to the shorter plants and loss of cover in the IR plots may be the burrowing and foraging habits of ice rats. A strong negative relationship between burrow density and vegetation cover in the IR plots indicates that burrowing reduces cover, possibly because of the physical clearing away of plants (Reichman and Smith, 1985;Hansell, 1993), and also because of the caving in of burrow systems (Grab and Deschamps, 2004). Moreover, tunnelling belowground destroys plants through attrition of root systems, resulting in bare-ground patches aboveground (Yair and Rutin, 1981;Alkon, 1999;Reichman and Seabloom, 2002). ...
Article
Rodents can contribute to habitat change through their activities. In the Lesotho Drakensberg, soil erosion has increased markedly recently, supposedly as a result of the combined activities of the ice rat Otomys sloggetti robertsi and domestic livestock. Ice rats are diurnal, herbivorous, burrow-dwelling rodents, endemic to the alpine regions of southern Africa. We erected exclosure plots to investigate the single or combined effects of ice rats and domesticated livestock on the vegetation and soil characteristics in their habitat and whether their activities potentially influence soil erosion. Contrary to our prediction, vegetation changes and soil movement were greatest in plots accessed only by ice rats. Therefore, ice rats are likely to be a major contributor to habitat change in the Lesotho Drakensberg because of their foraging and burrowing activities, and soil erosion is likely to be exacerbated by their increasing population numbers recently. Nonetheless, soil erosion is a complex problem involving several abiotic and biotic contributing factors, and long-term studies are required to fully understand the determinants underlying the causes of erosion in the Lesotho Drakensberg.
... 33 left-hand corner of the figure (R 2 = 0.49, p << 0.01), while the shaded area is the 95% confidence interval, and the dashed lines are the 95% prediction interval. Data Thief III (Tummers, 2006) was used to extract data from (Schook and Cooper, 2014) and (Crockett et al., 2015) High elevation wetlands are key in the provisioning of mountain watershed functions and services -they regulate runoff (Buytaert et al., 2006;Mosquera et al., 2016), provide habitat for rare and endangered species (Hauer et al., 2007;An et al., 2013), support the stabilization of riparian areas (Grab and Deschamps, 2004), and play a role in regulating greenhouse gases (Chimner et al., 2002;Millar et al., 2017). In this respect, changes in the functional capacities of mountain wetlands are likely to alter the overall functions of mountain ecosystems, which are themselves very important ecosystem service providers (Viviroli et al., 2003). ...
... As a result of wetland processes, alpine wetland soils serve a particularly important suite of functions in high elevation areas. For example, in Lesotho (southern Africa), wetlands soils are a key geomorphic regulator, helping to stabilize underlying mineral soils, thus preventing erosion and gully development, which would otherwise negatively impact watershed function (Grab and Deschamps, 2004). This outcome is largely the result of the presence of highly cohesive organic soils that maintain structural stability while damp, but become very fragile when dry. ...
Thesis
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Hydrological conditions play an important role in provisioning the exceptionally valuable ecosystem services and functions of wetlands. In alpine areas, wetland functions and services are expected to be very sensitive to climate-mediated changes in hydrology. However, few field studies of alpine wetland hydrology currently exist, thus limiting understanding of how wetlands will respond to warming and drying, and how their ecosystem services and functions will change. This study examines key processes contributing to the hydrological stability of alpine wetlands in Banff National Park, AB, Canada. During the two-year study, snowmelt timing differed by over three weeks, allowing for the examination of water table patterns under comparatively wet and dry conditions. Contrary to expectations, water table positions were relatively stable in each study year, particularly in the peat-bearing soils. Hydrophysical and hydrochemical data together provide evidence that the observed stability is in part due to groundwater contributions, which made up as much as 53% of the water budget in one peatland. Soil conditions also appear to play a role in stabilizing water table regimes. The results suggest that alpine wetlands, and peatlands in particular, may be more resilient to changes in climate than currently thought. Mineral wetlands, comparatively, may have limited adaptive capacity.
... Ice rats live in multi-male, multi-female colonies (kinship unknown) of between 4 to 17 adult individuals (Hinze et al. 2013), which jointly construct a complex underground burrow system with one to two nesting chambers (Willan 1990;Hinze et al. , 2013. Burrows provide refuge against lethal temperatures above-ground but are also prone to collapse (Grab and Deschamps 2004;Mokotjomela et al. 2009). Group living is driven by a need to huddle below-ground (Hinze et al. 2013) and not predation risk, since predators of ice rats are virtually absent in our study site due to low prey availability and local extirpation of predator populations by the local Basotho peoples (Willan 1990;Schwaibold and Pillay 2006). ...
... Individuals of larger colonies showed lower levels of burrow maintenance compared to those of small colonies, particularly in winter. Ice rat burrows are shallow (Willan 1990;, and burrow maintenance is important for maintaining the integrity of burrow systems that are prone to collapse from soil erosion (Grab and Deschamps 2004) and livestock trampling (Mokotjomela et al. 2009). In addition, burrows provide quick below-ground access to food patches, thereby reducing exposure to lethal lower temperatures aboveground, particularly during winter (Schwaibold 2005). ...
Article
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The relationship between group size and fitness has attracted much interest, with many attempts made to detect an optimal group size. Group size is determined by the benefits and costs influencing group formation, which also influences whether groups persist or fail. We investigated whether group size is associated with success (individual survival and reproductive output) in the African ice rat Otomys sloggetti robertsi. Ice rats form mixed-sex plural-breeding colonies that trade off the benefits of huddling below-ground against within-colony resource competition above-ground. We measured behavioural correlates of individual success in summer and winter, focusing on energy saving (basking), acquisition (foraging) and use (burrow maintenance, distance travelled for foraging) behaviours. We predicted that (1) individuals in larger colonies would forage and travel more to find food because of greater within-colony competition for resources; (2) individuals in larger colonies would bask less than individuals in smaller colonies because of the greater energy savings generated from huddling in larger groups; and (3) burrow maintenance would be greater in smaller colonies because of fewer individuals engaging in this task. We showed that colonies succumbed or persisted as a group (i.e. most individuals present or all absent). In particular, in both seasons, individuals in smaller groups (≤5 individuals) were more likely to fail, while those in larger groups (≥12 individuals) were more likely to persist. The persistence of colonies was positively predicted by foraging and negatively by basking. Foraging was greater in larger colonies and burrow maintenance was greater in smaller colonies. While females of larger colonies produced more offspring in total, reproductive output (per capita offspring production) was not correlated with colony size. Individual ice rats in larger colonies accrued fitness benefits, which were predicted, proximally, by greater foraging and possibly energy savings in larger huddling groups. Statement of significance What proximally determines the relationship between group size, individual success and colony persistence? In ice rats, individuals in larger groups persist, which is correlated with more foraging. Larger groups possibly enjoy the benefits of huddling in larger groups, which are re-channelled into energy-intense activities. Groups failed or persisted as a unit. Investigating the behavioural correlates of the relationship between group size and persistence provides insight into the proximal underpinnings of this relationship.
... Maphutseng, allowed for this high energy traction transport flood event deposition (Fig. 19;Nemec and Muszynski, 1982;Rydgren, 1988;Grab and Deschamps, 2004). The thinly interbedded, massive, calcretized LS units are interpreted as primarily pedogenically altered infill during intermittent periods of little fluvial flooding. ...
... The floodplain denudation model in this study, although localised, additionally provides proof of flashflood related gullying (and arroyos) in the ancient uEF FA 1 loessic-rich units. This flashflood driven gullying is a likely consequence of periods of increased erosion, which modern-day analogues have shown not to be limited to individual factors (Rydgren, 1988;Bull, 1997;Grab and Deschamps, 2004). In addition to tectonics, increased climatic aridity may well also play a role, with increased unconfined clay-rich palaeosols providing ample opportunity for significant denudation, ...
Thesis
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The Elliot and Clarens formations (Stormberg Group) of the Karoo Supergroup famously preserve not only a dynamic suite of depositional environments spanning the Late Triassic to Early Jurassic, but also boast a diverse assemblage of trace and body fossils. Due to the nature of these assemblages spanning the globally correlative Triassic-Jurassic Boundary (TJB) and end-Triassic Extinction Event (ETE), the accuracy of temporal placement and correlation via the stratigraphic framework is paramount. Yet, a distinct lack of robust temporal framework and inconsistencies between the bio-, magneto- and lithostratigraphic records persist. This project sought to provide localized context for three key fossil-bearing localities (southwestern Lesotho), which could thereafter be applied both at a regional and global scale. In-depth facies, palaeocurrent and architectural element analyses illustrated an overall increase in palaeoclimatic aridity, as evidenced by the change in depositional system from the meandering fluvial dominated lower Elliot Formation to the aeolian Clarens Formation. Detrital zircon geochronology ascertained a temporal framework ranging from the Norian to Pliensbachian (216.7-190.5 Ma) Elliot Formation to the Sinemurian to Pliensbachian (190.5-186.7 Ma) Clarens Formation. These temporal constraints also support the presence of a regional paraconformity at the lower and upper Elliot contact. The geochronology additionally indicated a shared source provenance of recycled grains from the Cape Supergroup and older Karoo strata, interspersed with direct source inputs from proximal magmatic/metamorphic provinces. Ultimately, the greater temporal and palaeoecological resolution provided by this study promotes the better understanding of the early Mesozoic history of southern Gondwana and lays the foundations for future geochronological investigations.
... Their extensive burrow systems contribute to soil turnover and aeration. However, when burrows collapse, the resulting gullies alter water flow, contributing to erosion (Grab & Deschamps 2004). (Mokotjomela et al. 2009). ...
... Marneweck and Grundling (1999;cited in National Wetlands Management Programme, 2005) calculate that Lesotho's wetlands currently store 36% less water than is their potential because of degradation. Many other observers have also noted evidence of degradation by livestock and rodents in Lesotho's alpine bogs and fens (Grab and Deschamps, 2004;van Zinderen Bakker and Werger, 1979;du Preez and Brown,2004).Degraded wetlands threaten not only diminish the quality of the water that enters Lesotho's highland streams-they will also cause an increase in the energy of water flowing downslope, carrying sediment and organic matter into the reservoir. The reservoir water will suffer quality losses from the introduction of organic matter while at the same time the reservoir will eventually lose active storage capacity. ...
... Because oxygen can penetrate into deeper layers of loose soils, decomposition is stimulated by the digging rodents. Furthermore, invasive plant species such as Chrysocoma ciliata colonise these desiccated mire areas (Grab & Deschamps 2004), posing a threat to the biodiversity of the alpine region. ...
Article
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Lesotho is a landlocked country located in the south-eastern interior of South Africa. It is mountainous, with altitudes ranging from 1388 to 3482 m a.s.l. This article focuses mostly on mires occurring above 2750 m a.s.l. in the alpine region of Lesotho, that are characteristically devoid of trees due to the high altitude. Mountain mires in Lesotho are usually fed by groundwater and intermittent runoff from adjacent slopes. Few of them are in near-pristine condition and most have been severely degraded. Erosion has enhanced the drainage and desiccation of peat resulting in combustion of peat layers at several sites. The main threats to the mires include overgrazing and trampling by domestic animals on communal land, increased development as a result of the Lesotho Highlands Water Project, and diamond prospecting and mining. Attempts at rehabilitation have met with varying degree of success. © 2015 International Mire Conservation Group and International Peat Society.
... Under the present-day conditions of normal rain and catchment-wide soil and water conservation, gully erosion rates are decreasing. Grab and Deschamps (2004) found that dryland plant invasions around grazing posts and heavily grazed areas on the slopes subsequently spread along alpine hydrological systems, particularly where gully erosion had created a suitable habitat. Cheng et al. (2006) measured an average gully length of about 19.6 m ha ?1 and an average soil loss of 8.8 m 3 ha ?1 due to ephemeral gully erosion on the Inner-Mongolia Plateau in northern China. ...
Article
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This study was aimed at assessing the causes of the gully erosion and its effects on the agricultural lands in the arid region of southeastern Iran. In this study, we have used geologic maps in scales of 1:50,000 and 1:250,000, aerial photographs on a scale of 1:20,000, field observation, and GPS (global positioning system). Three soil samples were taken from 25, 50, and 75% of the gully length at each location and analyzed for pH, electrical conductivity (EC), exchangeable sodium percentage (ESP), sodium absorption ratio (SAR), cation exchange capacity (CEC), calcium (Ca), and soil texture. The causes of gully erosion, its effects on agricultural lands, characteristics of the gullies, soil depth, and vegetation of each area were evaluated. The results show that several parameters, including poor rangeland vegetation cover, overgrazing, human activities, intensive and short-period rainfall, improper land use, improper irrigation design, improper discharge of water in the channels, and soil characteristics influence the gully erosion. Gully erosion causes severe damage to agricultural lands, including soil loss, increase in surface runoff, lower soil water-holding capacity, lower quality and quantity of water, lower groundwater table, and lower agricultural production. It increased migration from villages to cities and increased socioeconomic problems and poverty. It also caused substantial damages to construction sites such as bridges, roads, and settlements as well as rivers and reservoirs and increased sediment concentration in rivers.
... Hoag (2016) also found grazing intensity (around piospheres) along with nutrient enrichment and low soil moisture to be the most important drivers of shrub encroachment in a summer cattlepost area in the Mokhotlong District. Populations of shrubs can spread from cattleposts along the bare and dry sides of riverine erosion gullies and onto the denuded fringes of wetlands (Grab and Deschamps 2004) and are likely to move upwards and onto cooler slopes with future warming and continued atmospheric CO 2 enrichment (Morris 2017). ...
Article
The grasslands of the mountains in eastern Lesotho support large numbers of sheep, angora goats and other livestock during the summer, during which they are corralled nightly by herders at cattleposts. Few studies, however, have quantified the impact of grazing on the composition and structure of the mountain grasslands. Gradients of grazing and trampling intensity related to distance from 23 cattleposts in the subalpine and alpine belts (2 650–3 175 m above sea level) were examined to describe the long-term effects of livestock on unpalatable dwarf shrubs, bare area and plant species composition. The potential for shrub invasion and bare areas (low herbaceous cover) to develop was highest near cattleposts. Species composition also changed significantly along the grazing gradient, accompanied by a shift in dominants from grazing-sensitive to grazing-resistant grasses and shrubs. Species either decreased or increased monotonically along the grazing gradient or had an intermediate, unimodal response. The relative positions of species’ centroids along the grazing gradient were used to quantify their grazing sensitivity on a scale from 10 (most sensitive) to 0 (most resistant), which confirmed and contradicted previous classifications of their grazing responses. Basic ecological research on this important mountain grazing and catchment system is recommended.
... On cold days, a strong thermal gradient can develop between a cold peat surface and warmer peat at depth (Evans and Warburton, 2007) which together with an abundant moisture supply make ideal conditions for needle ice formation ( Fig. 1 (g)) (Outcalt, 1971). Needle-ice is important in producing eroding peat faces (Grab and Deschamps, 2004;Luoto and Seppälä, 2000;Tallis, 1973) with ice crystal growth gradually weakening and finally breaking peat soil aggregates and the subsequent warming and thawing weakening or loosening the fractured peat. The growth of needle ice can lead to a 'fluffy' peat surface that is loose and granular and vulnerable to being flushed off by overland flow events (Evans and Warburton, 2007;Li et al., 2018a). ...
Article
Peatlands cover approximately 2.84% of global land area while storing one third to one half of the world's soil carbon. While peat erosion is a natural process it has been enhanced by human mismanagement in many places worldwide. Enhanced peat erosion is a serious ecological and environmental problem that can have severe on-site and off-site impacts. A 2007 monograph by Evans and Warburton synthesized our understanding of peatland erosion at the time and here we provide an update covering: i) peat erosion processes across different scales; ii) techniques used to measure peat erosion; iii) factors affecting peat erosion; and iv) meta-analyses of reported peat erosion rates. We found that over the last decade there has been significant progress in studying the causes and effects of peat erosion and some progress in modelling peat erosion. However, there has been little progress in developing our understanding of the erosion processes. Despite the application of new peat surveying techniques there has been a lack of their use to specifically understand spatial and temporal peat erosion dynamics or processes in a range of peatland environments. Improved process understanding and more data on rates of erosion at different scales are urgently needed in order to improve model development and enable better predictions of future peat erosion under climate change and land management practices. We identify where further research is required on basic peat erosion processes, application of new and integrated measurement of different variables and the impact of drivers or mitigation techniques that may affect peat erosion.
... Due to the maritime location of many blanket peat environments, freezing is commonly diurnal and the effect of a single needle ice event can be multiplied many times through the winter season ( Figure 1). The importance of needle ice formation in producing eroding peat faces has been widely reported in peatlands such as eroding upland peatlands in the United Kingdom (Legg et al., 1992;Tallis, 1973), erosion of peat remnants in Finnish Lapland (Luoto & Seppälä, 2000), and alpine mires in Lesotho (Grab & Deschamps, 2004). The growth of needle ice can lead to a fluffy peat surface that is loose and granular and vulnerable to being flushed off by overland flow events (Evans & Warburton, 2007), with saturation excess overland flow being a dominant flow mechanism in blanket peat systems (Holden & Burt, 2003). ...
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Freeze-thaw processes play a role in increasing erosion potential in upland areas, but their impact on overland flow hydraulics and fluvial erosion processes are not clearly established. We provide the first quantitative analysis demonstrating that needle ice production is a primary process contributing to upland peat erosion by enhancing peat erodibility during runoff events following thaw. To quantify the effects of needle ice on peat physical properties, overland flow hydraulics, and erosion processes, physical overland flow simulation experiments were conducted on highly frost-susceptible blanket peat with and without needle ice processes. For each treatment, overland flow rates of 0.5, 1.0, and 2.0 L/min and slopes of 2.5° and 7.5° were applied. Peat erodibility, sediment concentration, and sediment yield were significantly increased in treatments subjected to needle ice processes. Median peat losses were nearly 6 times higher in peat blocks subject to needle ice processes than in peat blocks not subject to needle ice processes. Needle ice processes decreased mean overland flow velocities by 32–44% via increased hydraulic roughness and changes to surface microtopographic features, with microrills and headcut development. Needle ice processes increased the hydrodynamic force of shear stress by 55–85%. Erosion rates under needle ice processes exhibited a significant linear relationship with stream power. Our findings indicate that models of overland flow-induced peat erosion would benefit from a winter component that properly accounts for the effects of needle ice processes on peat erodibility and erosion.
... Wherever the mineral bank and its immediate top peat were dry, the peat layer that constitutes a series of roughly paralleled stratification or stratigraphy (Hughes et al., 2000) showed horizontal cracks near or at the bottom of the peat or a few small holes (Fig. 10). These cracks and/or small holes that have been also reported in other peatlands (Grab and Deschamps, 2004;Holden and Burt, 2002) suggested that the preferential flow (or pipe flow), which moves much faster than groundwater flow (Holden and Burt, 2002;Holden et al., 2001;Wallage and Holden, 2011), facilitated water to drain quickly and resulted in the dried minerals at these locations. Our data and field observation suggested that enhanced groundwater flow through type-II gullies created by intense erosion processes could be a significant cause for it, though data collected over longer time periods (e.g., two to three years) are required to further confirm our findings. ...
Article
Study region: The study area was in the upland peatland within the Zoige basin with elevations ranging between 3400 and 3800 m. It is located in the source area of Upper Yellow River that is developed on the Qinghai-Tibet Plateau, China. Study focus: We examined possible influence of two different types of gullies on groundwater hydrology in this alpine peatland, the gullies whose beds cutting through the peat layer and those whose beds are within the peat layer. We measured saturated hydraulic conductivity, hydraulic head, and water table levels both vertically and horizontally in three representative sites distributed in the study area representing blanket peatland and peats surrounded by two types of the gullies during May 11-23, 2017. Using these data, we showed that different patterns of these parameters in both directions may be clearly observed among the three sites. New hydrological insights for the region: We have shown for the first time in this region that (1) gullies with the bed cutting through the peat layer may have profound impact on peat groundwater hydrology; (2) groundwater seepage at the bottom of the peat layer may be enhanced by gullies with the bed cutting through the peat layer; and (3) increased groundwater seepage could be an additional cause for peatland degradation during the prolonged dry and cold period of a year.
... Therefore, it was hypothesized that preferential rodent burrowing at lobe fronts could provide a destabilizing trigger mechanism through the disruption of the supporting vegetation root mat and the consequent reduction of the soil shear strength. Similarly, preferential drainage along burrow channels could lead to localized front collapse and enhanced sediment removal (Thorn, 1978;Grab and Deschamps, 2004). However, our results provide no support for these hypotheses, but rather suggest that lemming burrows do not accelerate the degradation of solifluction lobes. ...
Article
Burrowing mammals often have considerable geomorphological impacts, and their tunneling activities may decrease the stability of landforms. We document the spatial distribution of Norwegian lemming burrows in a subarctic alpine meadow to determine the preferred locations for burrow entrances and to examine the potential for burrowing to decrease the stability of periglacial landforms at the site. Burrow entrances were disproportionately common into the base and sides of landforms (>68% of burrows), probably reflecting the lower energetic cost of moving soil horizontally, rather than vertically, out of burrows. Most burrow entrances (>60%) were also located under large rocks, which probably improve burrow stability by providing a firm ceiling to the entrance. Field observations show that these burrows are relatively stable, as only 3% were associated with any signs of increased erosion or landform instability. Therefore, in contrast to some previous studies, and despite burrowing being concentrated on landforms, we suggest that these rodents have little direct impact on landform integrity at this site. © 2011 Arctic, Antarctic, and Alpine Research.
... Wetlands are very vulnerable ecosystems that are greatly affected by both climate change and human actions . The wetlands that have been identified in the alpine highlands of Lesotho, where Afriski is located, have been classified as mires or peatlands that endure despite harsh climatic conditions of cold surface and air temperatures accompanied by frequent occurrences of ground-level freezing (Grab and Deschamps, 2004). If wetlands are not conserved issues of water extraction, invasive and alien fauna abundances, amplified eutrophication and nutrient imbalances, caused by the synergy between humans and climate change, can be amplified (Green et al., 2017). ...
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Climate change poses a number of challenges for the global tourism industry, with site-specific issues for many tourism destinations. The snow-based tourism industry is particularly vulnerable to the consequences of climate change, notably through rising temperatures and alterations in natural precipitation patterns. Afriski is a mountain ski resort established in the Lesotho Highlands that is facing the challenges of a changing climate. Afriski is a unique tourism experience as one of only two ski resorts in sub-Saharan Africa. This resort is actively addressing the challenges of climate change through the artificial production of snow, the temporal manipulation of the skiing season and through diversifying their tourist product offerings. Adaptation mechanisms implemented as a means of addressing climate change are critical to the longevity and success of snow-based tourism resorts and for the tourism industry in general. This study makes use of a mixed-method approach comprising face-to-face, semi-formal interviews with managerial stakeholders, questionnaire surveys completed by tourists and an analysis of climatically relevant comments posted to TripAdvisor. Tourist perceptions, as determined by this study, showed general concerns regarding climate change and tourism. Tourist perceptions however, also revealed high levels of satisfaction regarding the adaptation mechanisms implemented in order to address the challenges of climate change. This unique case study investigates the impacts of climate change on a snow-based resort in southern Africa while contributing to the body of research on climate change and tourism in the global south. iii
... The montane wetlands on the Lesotho part of the Maloti-Drakensberg region have been regarded for a long time as an important resource for livestock grazing (van Zinderen Bakker and Werger, 1974;Du Preez and Brown, 2011). In fact, much of the livestock grazing in the mountains of Lesotho takes place within wetlands, which harbour the most palatable vegetation (Grab and Deschamps, 2004). ...
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Classification and description of wetland vegetation provides an understanding of the wetland vegetation–environment relationships, as well as their spatial variation and information for water resource management and biodiversity conservation. In this study, the montane palustrine wetland vegetation types of the Maloti-Drakensberg region and surrounding areas are discussed based on a phytosociological approach. The montane subset of the National Wetland Vegetation Database of South Africa was selected and supplemented with the new data collected from the Lesotho component of the Maloti-Drakensberg region. This montane subset was collected using the Braun-Blanquet method for vegetation and recommended methods for wetland environmental data. The new vegetation data from Lesotho were collected using the same methods used for the historical data. The combined data were then analysed mainly by means of clustering and ordination techniques. Forty-two wetland plant communities were obtained from the cluster analysis and these were summarised into sixteen community groups. These community groups are diverse in terms of species richness and also exhibit significant variation along the altitudinal gradient, mainly due to variations in environmental conditions that include temperature, parent material and the amount of precipitation, among other factors. The ordination revealed that the variation in the wetland vegetation is mainly explained by altitude, longitude, latitude, nitrogen content, soil depth, inundation depth and electrical conductivity, but slope, pH, sodium content, total organic carbon, soil texture and degree of wetness are also important. In terms of species composition, high altitude plant communities were distinctively different from those at low altitudes. Regarding distribution, montane wetland vegetation was found to be more concentrated in the Maloti-Drakensberg region than the rest of the region, although some community groups also occurred in the lowlands of Lesotho and all the provinces of South Africa. The diversity exhibited by these wetlands, coupled with their restricted distribution at high altitudes, capacity to support endemic species, their role in water resources and provision of other ecosystem services, point to the high conservation value associated with these ecosystems.
... e mean winter monthly temperatures range from −6.3°C to 5.1°C, and the mean summer maximum temperatures range from 16.5°C at high altitudes to 29°C in the lowlands [39]. Lesotho has a highly degraded mountain landscape [40,41]. ...
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Soil organic carbon constitutes an important indicator of soil fertility. The purpose of this study was to predict soil organic carbon content in the mountainous terrain of eastern Lesotho, southern Africa, which is an area of high endemic biodiversity as well as an area extensively used for small-scale agriculture. An integrated field and laboratory approach was undertaken, through measurements of reflectance spectra of soil using an Analytical Spectral Device (ASD) FieldSpec® 4 optical sensor. Soil spectra were collected on the land surface under field conditions and then on soil in the laboratory, in order to assess the accuracy of field spectroscopy-based models. The predictive performance of two different statistical models (random forest and partial least square regression) was compared. Results show that random forest regression can most accurately predict the soil organic carbon contents on an independent dataset using the field spectroscopy data. In contrast, the partial least square regression model overfits the calibration dataset. Important wavelengths to predict soil organic contents were localised around the visible range (400–700 nm). This study shows that soil organic carbon can be most accurately estimated using derivative field spectroscopy measurements and random forest regression.
... It was initially assumed that C. ciliata is a karroid invasive that was introduced anthropogenically in the high-altitude alpine areas of Lesotho within the last century, but fossil pollen records have since indicated that the species has naturally been present over a long period of time (Fitchett et al. 2017). Despite being a natural component of the vegetation, C. ciliata is reportedly establishing itself on heavily grazed areas in the high-altitude alpine areas of eastern and southern Lesotho (2 400 to 3 200 m above sea level) and is spreading along alpine hydrological systems, particularly where gully erosion has created a suitable habitat (Grab and Deschamps 2004). ...
Article
The Lets’eng-la-Letsie wetland is an official Ramsar site, but the wetland and upland catchment areas suffer from overgrazing, erosion and over exploitation. Chrysocoma ciliata has a reputation as an unpalatable invader and is particularly common on the drier northern slopes. The objectives of the study were to quantify the phytomass of this shrub with the aid of a developed allometric phytomass quantification technique and to evaluate the ecological significance of this shrub within the area. Highly significant (p < 0.001) positive regressions with coefficients of determinations as high as r ² = 0.94 between phytomass and plant canopy diameter were achieved. The upland slopes support a high density of more than 35 000 C. ciliata plants ha⁻¹ with a phytomass of more than 3 600 kg DM ha⁻¹ and a correspondingly low herbaceous phytomass of 446.57 kg DM ha⁻¹. The edible parts of the plants (flowers, leaves and shoots <2.0 mm in diameter) were estimated to be 1 198 kg DM ha⁻¹, with a crude protein content of 8.84%. There was evidence that C. ciliata is intolerant of wet conditions and the degradation of the catchment areas will result in drier soil profiles, which will favour the further spread of this species.
... Overgrazing is often cited as the main cause of both sheet and gully erosions in mountainous areas. Cattle trampling and overgrazing are considered as the main degrading cause in the Southern part of Africa (Grab and Deschamps, 2004) as well as in Ethiopia (Nyssen et al., 2004). It is known to be an old problem in the Mediterranean basin, for example in the French Alps (Descroix and Gautier, 2002), in Spain (Nogueras et al., 2000;Kirkby et al., 2002), in Italy (Moretti and Rodolfi, 2000;Torri et al., 2006), in Portugal, and in North Africa (Masson, 1971;Roose and De Noni, 1998). ...
Article
As most mountains in tropical and subtropical zones, the Western Sierra Madre suffers active present erosion, which may create some constraints to the social and economic development in the area.The objectives of this study of soil degradation in the Western Sierra Madre, are to determine the respective roles of gully and sheet erosion. This research is based on field observations, field measurements of runoff and, soil losses at the plot, as well as the watershed scales as an analysis of an exhaustive census of the few gullies located in an experimental area.Measured soil losses in the Western Sierra Madre are high although there are few gullies. Most of the sediment yield seems to originate in widespread degraded areas where stoniness is the main evidence of a previous stage of erosion. Previously overgrazing and deforestation were determined as the factors of the appearance of new soil surface characteristics which explain the high runoff and sediment productions. The soil compacted by cattle trampling reduces infiltration. The decrease of the vegetation cover triggers a rise in the splash effect and thus, a soil sealing.These processes induce an increase in runoff and soil losses. The main erosion type has been described as sheet erosion: it is characterised by the removal of fine soil particles and the remains of gravels, pebbles and blocks, which constitute a pavement on the soil. Gullies generally appear on the bottom of wide valleys and depressions, where soils are thick. It is shown that sheet erosion is two orders of magnitude higher than gully erosion at the hillslope scale.Due to the spatial distribution of land use and the geological context such as the heavily degraded areas close to the main rivers, the reduction of runoff and soil loss rates within the extension of a considered area, commonly observed in hydrology, only applies up to the elementary catchments scale (1 to 50 km2). Above this area, runoff coefficient and soil loss rates increase.
... Erosion processes in the Maluti Mountains in the Kingdom of Lesotho, southern Africa, have been the focus of numerous geomorphological and climatological studies (Van Zinderen Bakker, 1984;Grab & Deschamps, 2004). Recently, researchers in the School of Geography, Archeology and Environmental Studies of the University of the Witwatersrand noticed a concerning increase in the rate of erosion, which coincided with atypically mild winters (S. ...
Article
Recent work has indicated that the southern African ice rat (Otomyssloggetti robertsi) is responsible for negative habitat change due to its foraging and burrowing activities in the Lesotho Highlands. Previous work has only focused on short-term ( ≤ 1 year) monitoring and thus the impact of such rodent activity over longer temporal scales remains unknown. To this end, the current study evaluates vegetation cover and O. s. robertsi's burrowing over a 10-year period (1998–2009) across a portion of a wetland fringe/wetland in eastern Lesotho. A 6 m × 11 m plot was established in 1998 and marked out with permanent stakes. Percentage cover and number of tunnels were recorded, with repeat measurements taken in 2001, 2005 and 2009. The findings indicate an overall 69.2% increase in vegetation cover and associated 71% decrease in burrow densities between 1998 and 2009. The area monitored closest to the wetland fringe recorded the most substantial burrow density decrease (by 80%) and vegetation recovery (by 43%) within a three-year period from 1998 to 2001. With a slight shift of burrow density increases towards the wetland centre, particularly between 2001 and 2005, the standard deviation of burrow density (per m) from the wetland periphery towards the wetland centre had decreased from 1.25 to 0.32 over the 10-year period. It is proposed that the environmental influence of O. s. robertsi may be less dramatic at some landscape and longer temporal (i.e. years rather than months) scales due to spatial shifts of colonies, bioengineering and rapid vegetation recovery at abandoned, formerly ‘degraded’ burrow sites.
Article
Lesotho has only one wetland designated as a Ramsar site, found at Letšeng-la-Letsie, which is located within the Maloti-Drakensberg region. Despite its designation as a wetland of international importance, little is known about its ecology and biodiversity. Information on wetland biodiversity is crucial for monitoring and conservation planning. This study investigated the vegetation-environment relationships in the Letšeng-la-Letsie Wetland, Lesotho. Vegetation and environmental data were collected using the Braun-Blanquet approach and standard methods, respectively. The data were analysed using cluster analysis and ordination techniques. The study recorded a total of 68 plant species from 50 genera and 23 families in the wetland, with Cotula paludosa, Eragrostis caesia, Haplocarpha nervosa and Trifolium burchellianum as some of the most dominant species. Three distinct plant communities were described: Potamogeton pusillus–Ficinia cinnamomea, Helichrysum glaciale–Eragrostis caesia and Cotula paludosa–Trifolium burchellianum. The communities and species richness recorded revealed high diversity in this wetland when compared to similar wetlands within the Maloti-Drakensberg region. Ordination revealed that species diversity and the plant communities are mainly influenced by altitude, inundation depth, mottling depth, longitude and various edaphic attributes (potassium, total organic carbon, sodium and cation exchange capacity). This study provides the baseline information, which is essential for planning, monitoring and managing this wetland of international importance. In addition, the presence of introduced invasive species suggests the need to practically protect this wetland by implementing the developed management strategies. This will ensure the conservation of biodiversity, sustainable ecosystem service delivery and compliance with the Ramsar Convention requirements.
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The Geomorphology of Upland Peat offers a detailed synthesis of existing literature on peat erosion, incorporating new research ideas and data from two leading experts in the field. Presents the most detailed and current work to date. Written in a style that is both intelligent and accessible. Fully illustrated with original drawings and photographs. Relevant and information for a broad audience working on organic sediments in various environments.
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Although palustrine wetlands cover only about 6% of the earth’s surface, they are among the most productive and socio-economically valuable ecosystems globally. However, these ecosystems are facing various threats. The current study uses literature and field observations to explore the montane palustrine wetlands of Lesotho, in terms of their distribution, coverage, vegetation, ecosystem services, status, major threats and conservation. The study found that despite occurring throughout the country, the highest density of the wetlands is associated with the central and eastern parts, and generally declines towards the south and west as the rainfall decreases and the altitude becomes lower. The wetlands are rich in plant diversity and deliver various ecosystem services, including water, livestock grazing, harvestable resources, carbon storage and crop cultivation. Therefore, these wetlands play an important role at the local, national and regional scales and form an important water resource for Lesotho, South Africa and Namibia. Despite their value, some of the wetlands have been lost and the condition of those remaining is declining, mainly due to anthropogenic factors. Nevertheless, various conservation and restoration activities have been implemented in an attempt to conserve and manage these ecosystems. Despite these efforts, wetland loss and degradation continue, to the detriment of wetland biodiversity and ecosystem service delivery. Thus, this study recommends the scaling-up of the conservation efforts, as well as mainstreaming wetland conservation and management, including emphasising the wise use of these systems. Emphasis should be placed on regulating livestock grazing and trampling, harvesting of natural resources, infrastructure development and cultivation in the wetlands.
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Erosion and the associated loss of carbon is a major environmental concern in many peatlands and remains difficult to accurately quantify beyond the plot scale. Erosion was measured in an upland blanket peatland catchment (0.017 km2) in northern England using Structure‐from‐Motion (SfM) photogrammetry, sediment traps and stream sediment sampling at different spatial scales. A net median topographic change of –27 mm yr–1 was recorded by SfM over the 12‐month monitoring period for the entire surveyed area (598 m2). Within the entire surveyed area there were six nested catchments where both SfM and sediment traps were used to measure erosion. Substantial amounts of peat were captured in sediment traps during summer storm events after two months of dry weather where desiccation of the peat surface occurred. The magnitude of topographic change for the six nested catchments determined by SfM (mean value: 5.3 mm, standard deviation: 5.2 mm) was very different to the areal average derived from sediment traps (mean value: –0.3 mm, standard deviation: 0.1 mm). Thus direct interpolation of peat erosion from local net topographic change into sediment yield at the catchment outlet appears problematic. Peat loss measured at the hillslope scale was not representative of that at the catchment scale. Stream sediment sampling at the outlet of the research catchment (0.017 km2) suggested that the yields of suspended sediment and particulate organic carbon were 926.3 t km–2 yr–1 and 340.9 t km–2 yr–1 respectively, with highest losses occurring during the autumn. Both freeze–thaw during winter and desiccation during long periods of dry weather in spring and summer were identified as important peat weathering processes during the study. Such weathering was a key enabler of subsequent fluvial peat loss from the catchment.
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This study was aimed at assessing the land use and cover change and its effect on gully expansion in an agricultural and woodland tropical watershed. We used the case study of Luzinzi watershed in South-Kivu, eastern Democratic Republic of Congo (DRC) where gullies are in development. We used very high-resolution (VHR) images downloaded from Google Earth and Unmanned Aerial Vehicles (UAV) images. ArcGIS 10.7 software helped for spatial analysis and images georeferencing while ENVI 5.3 tools were used for classification. The gullies were then digitized and characterized to determine their width, length, depth, surface and volume. The digital elevation model (DEM) was used to determine the contributing area as well as the slope at the gully head. The land use at the headcuts and in the gully was extracted from the different land uses obtained from classified images and validated by field measures. Results showed significant changes in land use and land cover throughout the watershed; changes that affected gully expansion. From 2011 to 2020, number of gullies passed from 38 to 201. These gullies were increasing not only in number but also in characteristics such as length, and head cut. Their volumes increased from year to year in the same trend as woodland and forest reduction. Forest played important role in gully stabilization: gullies located in forest presented a linear retreat rate (∼4.6 m) than those in other land uses (∼2.4 m) from 2010 to 2020. The forest cover reduced gully surface and linear rate while the depth rate still increased. A forest cover of only ∼10% led to an expansion of ∼700 m³ yr⁻¹ and which was further reduced to 300- 400 with 30% coverage. Forest cover at the head cut and in the contributing area helped to stabilize gullies. The permanent maintenance of forest and woodland covers as well as the reduction of anthropogenic activities in some gullies are to be promoted at the watershed scale along with other measures to contribute to the land resource management in the region.
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The paper presents a sedimentological, palynological, and phytolith record from a 13 m deep Holocene sedimentary sequence, located in the Tsoaing River valley, southwestern Lesotho. Six conventional radiocarbon and two AMS dates provide a relatively high resolution Holocene record for the sedimentary sequence, ranging from ca. 12 000 to 4000 years BP. Pollen is absent in the upper section but present in the lower 2 m, confirming terminal Pleistocene/Holocene conditions reported in previous published pollen and charcoal records from the region. The absence of pollen in the upper layers of ca. 9000 years BP and younger suggests that conditions over southwestern Lesotho throughout much of the Holocene was typified by a seasonal climate that prevented long-term preservation of plant remains, although other plant material like robust spores, microscopic charcoal, and phytoliths withstood oxidation. Sedimentological and phytolith results suggest that the period from ca. 8600 to 8450 years BP experienced rapid environmental change towards drier conditions. Phases of chemical disintegration with organic input (including local swamp phytoliths) are suggested at ca. 7000 years BP and again after 4500 years BP.
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The Drakensberg, adjoining the eastern Lesotho highlands, have recently been proclaimed as South Africa's fourth World Heritage Site. The objective of this paper is to demonstrate the potential value of intra-disciplinary and problem-orientated geographical research for this region. Such a methodological framework is demonstrated through raising questions, providing brief case-study examples and applying integrated approaches to human ecological dynamics identified from the Sani plateau region. It is found that the interactions between the natural and the social systems in eastern Lesotho are complex and offer substantial opportunities for integrated research. It is suggested that an improved understanding of the broader environmental dynamics may offer practical value in the management of natural resources in this mountain region.
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Why do different plant species thrive where they do? This is a difficult question to answer because plants have invaded new niches and subsequently evolved to become better adapted within those niches. Distinguishing the traits that allow successful invasion and those that are evolved adaptations to current environments is not usually possible. We attempt to identify life history components that allow successful invasion by analysing the life history variables and ecological requirements of plant species that have successfully invaded the U.K. in recent years. The British flora is uniquely suited for this analysis because we have precise information on the dates of arrival, rates of spread and final spatial distribution of all our alien vascular plant species. Data on alien plants controls for evolution after invasion because there has been relatively little time for evolution to occur. We use modern phylogenetically-based comparative methods in an attempt to tease apart those components of life histories that have allowed successful invasion (large seeds, tall stature, protracted seed dormancy) from those that are irrelevant (dispersal syndrome, mating system, leaf shape).
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This paper presents, in brief, the research into runoff and soil erosion presently being carried out in the Maphutseng area in Lesotho, Southern Africa. The research has a multilevel approach, i.e. it measures runoff and soil erosion at different scales in the same geographical area. A subcatchment, 5.4 ha in size, is sampled along with 12 runoff plots. The plots are located on three different soil types and have two different agricultural managements. Each trial has two replicas. The results, which are still preliminary, show that 10% of the rainfall ran off and that the soil loss was 16.4 t/ha from the subcatchment. The plots lost on average 0.65 t/ha and there was no significant difference between the two management types.
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A simple two-dimensional mathematical model was used to forecast soil moisture flux and runoff events. The basic goal was to use only meteorological data that are likely to be available in those environments where soil erosion is an acute problem, i.e. usually a low-tech setting. The parameters were combined with information from a very limited number of undisturbed soil samples and estimates or literature information on additional background information for the parametrisation of the model. The results of the modelling show a good agreement between predicted and observed number and time of runoff events. Generally there was also a good agreement between predicted and observed runoff volumes. Uncertainties remain due to gaps in the series of field observations. Compared to conventional concepts like "erosive rains" the simple mathematical model produced by far a better agreement with reality.
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Precipitation data for 8 stations in the lowland and foothill regions of Lesotho were analysed to characterise the geomorphological significance of precipitation from a soil erosion perspective. Lacking long series of recording rain gauge data, short series of intensity recordings were used to establish a relationship between daily amounts and maximum storm intensity. Applying this information on longer series of daily rainfall data made it possible to estimate the frequency with which intensive storms occur that are likely to contribute to soil erosion. Frequency analysis based on the partial duration technique made it possible to determine the recurrence intervals of rainstorms of various 30-minute magnitudes. The results show that for all sites it can be expected that rainstorms with a maximum 30-minute intensity exceeding 25 mm/h are likely to occur at least once each year. The likelihood of high intensities is highest during December-February with considerably longer recurrence intervals for the onset and end of the wet season. recurrence intervals are longer for sites located in the foothill and mountain regions of the country. Considering the severe status of soil erosion in Lesotho it is unlikely that rainfall intensity conditions should be regarded as the fundamental cause of soil erosion.
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Documents the types, rates and extent of soil erosion and sedimentation within the Roma Valley/Maliele and Khomo-khoana catchments in Lesotho. The drainage areas studied range from 0.2 to 57 km². All are located within lowlands and foothills regions. The rates of reservoir sedimentation vary from 0 to 25 cm.m⁻²y⁻¹. These rates correspond to sediment yields of 0-1800 t.km⁻²y⁻¹. The suspended sediment loads range from 270-1400 t.km⁻²y⁻¹. The present rates of gully growth (headward extension) vary from a few decimetres to about a metre per year for the majority of the presently active gullies. -from Author
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Four types of gullies are 1) V shaped gullies formed by overland flow in material which does not become increasingly erodible with depth; 2) U shaped gullies occurring mainly in deep weathering products and formed principally by overland flow; 3) U shaped gullies where subsurface flow and piping are important processes in dispersive materials and 4) arroyos type gullies in valley bottoms. The rates of gully growth and the potential erosion hazard is discussed in relation to these gully types. -from Authors
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This paper presents, in brief, the research into runoff and soil erosion presently being carried out in the Maphutseng area in Lesotho, Southern Africa. The research has a multilevel approach, i.e. it measures runoff and soil erosion at different scales in the same geographical area. A subcatchment, 5.4 ha in size, is sampled along with 12 runoff plots. The plots are located on three different soil types and have two different agricultural managements. Each trial has two replicas. The results, which are still preliminary, show that 10% of the rainfall ran off and that the soil loss was 16.4 t/ha from the subcatchment. The plots lost on average 0.65 t/ha and there was no significant difference between the two management types.
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The mountain catchments above 2 750 m a.s.l. in eastern Lesotho are a proclaimed Managed Resource Area (MRA) as a result of official concern about degradation of the grasslands of the alpine belt, and of recent parastatal interventions in the local livestock economy. However, the demarcation of the MRA may be inappropriate because it ignores recent changes in the transhumance system which threatens to cause greater degradation of the grasslands in the subalpine belt, particularly in the lower subalpine zone. In response to a variety of ecological and social factors, Basotho have modified the transhumance system by establishing winter grazing posts in this zone which lies between the summer grazing post areas in the subalpine zone and the alpine belt and the villages. The former areas are now used more intensively than the latter areas, thereby increasing the potential for greater degradation in the lower subalpine than in the upper subalpine zone and in the alpine belt. It is argued that the conservationist perspective, by which the MRA was demarcated needs to be broadened to include these lower valleys in view of these ecological dynamics.
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Detailed examination of sediments retained in two north-facing cirques south of Sani Top (latitude 29°30'S; longitude 29°2'E) has been undertaken as a contribution to the Late Quaternary history of highland Lesotho. The sediments are exposed by gullies incised through the deposits. Nine sections are discussed in detail. Inorganic sediments, matrix-supported diamictons and derived orange gravels as well as organic dark clays and peats are present. Eight dated organic samples range in age from 13490BP, currently the oldest organic carbon date from highland Lesotho, to 2310 BP. The sedimentary sequences are interpreted to present a sequence of Late Quaternary events with climatic implications.
Article
Biological invasions are a threat to ecosystems across all biogeographical realms. Riparian habitats are considered to be particularly prone to invasion by alien plant species and, because riparian vegetation plays a key role in both aquatic and terrestrial ecosystems, research in this field has increased. Most studies have focused on the biology and autecology of invasive species and biogeographical aspects of their spread. However, given that hydrogeomorphological processes greatly influence the structure of riparian plant communities, and that these communities in turn affect hydrology and fluvial geomorphology, scant attention has been paid to the interactions between invasions and these physical processes. Similarly, relatively little research has been undertaken on competitive interactions between alien and native riparian plant species. Further research in these fields is necessary at a variety of spatial and temporal scales before the dynamics of riparian invasions, and their impacts, can be properly understood.
Article
With global periglacial geomorphology undergoing significant advancements, it is appropriate to review the past and current status of such research in Africa. A brief historical overview of research outputs and approaches is presented for the respective African regions. Potential future quantitative periglacial research needs and approaches identified for Africa include: the examination of active periglacial processes, the identification of landforms and ground-ice forms, the potential for environmental change and the palaeoenvironmental reconstruction, and the application of periglacial studies. It is demonstrated that while periglacial geomorphology has progressed significantly in southern Africa, there has been little or no advancement elsewhere on the continent over the last two decades. None the less, on a more positive note, it is concluded that Africa has considerable potential in future global periglacial research.
Article
Floodplains are unique ecosystems because of their Linear form, the sometimes extreme dynamism of their geomorphology and because they process large fluxes of energy and materials from upstream areas. This article focuses on the importance of hydrological inputs to floodplains through 1) their influence on the arrangement of landforms and vegetation communities and 2) the connections between flooding regimes and the regeneration and turnover time of floodplain vegetation. Many researchers have demonstrated close links between the arrangement of vegetation communities and sedimentary landform types, elevation, soil characteristics, tolerance to flooding and availability of soil moisture. It is suggested that plants on floodplains are found along a combined gradient of available moisture and oxygen which can be viewed simultaneously as a flooding frequency gradient and a complex soil moisture gradient. Discussion of experimental work on floodplains demonstrates the importance of these gradients to a range of floodplain species in different environments. The relationships between these environmental gradients and the apparent high level of overlap between planform patterns of landforms and vegetation communities on floodplains are related to lag times in different parts of vegetation communities. mood regimes greatly influence the availability of areas suitable for vegetation regeneration from year to year and the age structure of floodplain communities over decadal time frames. Biotic factors also influence biogeomorphological relationships on floodplains and range from sediment-trapping by vegetation to the impacts of beaver and grazing animals on floodplain hydrology and vegetation. Restoration of floodplains is high on the agenda in many countries and it is argued that, for sustainable results, restoration of hydrological pathways is essential. Planned flood releases below darns in several African countries have had varied success rates but the development of models for managing flows to achieve different restoration targets is the start of an integrated approach to restoring complex floodplain ecosystems.
Article
The scientific and human dimensions of global change have many overlapping themes which offer a focus on processes occurring at the continental surface. Soil moisture is of critical importance to the physical processes governing energy and water exchanges at the land/air boundary. Soil moisture controls the extent to which plants can exploit sunlight in photosynthesis and the effectiveness with which agriculture, forestry and freshwater resources can be developed. The importance of the soil moisture to many, diverse communities has resulted in a very large collection of numerical models all of which simulate soil moisture. This paper outlines why and how a series of soil moisture simulation intercomparisons were conducted in a one-year exercise jointly sponsored by the International Geosphere Biosphere Programme and the World Climate Research Programme.
Article
A 12 month study on the thermal regime for a thufa apex and its adjoining depression was undertaken in the Mashai Valley (∽2950 m ASL), Lesotho Highlands, during 1993–94. Pronounced temperature differentials occurred during the winter months when apexes were frozen for several weeks and depressions remained predominantly unfrozen. The data show that existing micro-topography is an important factor controlling the maintenance or further development of thufur in marginal periglacial environments. © 1997 John Wiley & Sons, Ltd. Une étude du régime thermique du sommet d'un thufa et de la dépression qui le borde a été poursuivie dans la vallée de Mashai (2950 m au-dessus du niveau de la mer) dans les hautes terres du Lesotho pendant 12 mois en 1993–94. Des différences de température importantes existent pendant les mois d'hiver quand les sommets des thufurs sont gelés pendant plusieurs semaines et que les dépressions restent non gelées. Les données montrent que la microtopographie existante est un facteur important contrôlant la conservation et le développement des thufurs dans les environnements périglaciaires marginaux.
Article
The Kingdom of Lesotho has a well-established international reputatino as an exceptionally eroded landscape. Since the turn of the century there have been reports of increasing degradation and blame has been laid at the feet of the land users. Bad or "primitive' farming methods and overgrazing have been repeatedly identified as the agents of destruction. However, these features have been present since the 19th century. -from Author
Article
Information on rainfall intensity is regarded as one of the essential factors for predicting soil erosion. Since many sites lack information regarding the intensity of rains, estimates have to be made. The study investigates the relationship between daily amounts of precipitation and rainfall intensity based on a discontinuous series of charts from 1985–1994 at Roma Campus, Lesotho. Records of daily precipitation during the period 1962–1994 were used to determine the frequency distribution of daily precipitation for individual months. Relationships between total daily amount and maximum storm intensity during 15, 30 and 60 minutes were established which may be used for intensity estimates at sites lacking intensity records. It is also shown that standard erosivity indices may severely underestimate the number of days with erosive conditions. If, in contrast, the actual infiltration capacity of the soils is compared to rainfall intensity, the number of days with erosive conditions for grazing land increase from 4 to 50 days/year. The corresponding figure for farmed land would be 10 days/year.
Article
Five vegetation communities in the alpine catchments of Lesotho were identified by hierarchical classification of the botanical composition data. Discriminant analysis indicated that these communities occupy particular topographic positions. The community‐environment relationships identified in this study were similar to those reported from other alpine areas of Lesotho. Grasslands at high altitudes are temperate in nature, with a high proportion of C3 grass species. Below 2 950 m on the warmer aspects and below 2 750 m on south‐facing slopes, subtropical grass species (C4) dominate the sward. Within the temperate and subtropical vegetation belts, slope orientation dictates the proportion of C3 species present in the sward. It is proposed that topography acts to modify the factors that directly influence plant growth by modifying solar radiation patterns.
Article
Field data from south-eastern Alexander Island, Antarctica, are used to develop a model for the formation of asymmetrical valley-side slopes. Enhanced weathering and transport causes reduction in the gradient of north-facing slopes. Conversely, the relatively inactive south-facing slopes maintain their steep gradients. The application of this model for formation of the observed asymmetry in the high altitude regions of the Drakensberg mountains during the Pleistocene is considered. It is proposed that enhanced weathering and transport reduces the gradient of north-facing slopes whereas the south-facing slopes remain relatively protected environments. -Author
Article
Considering the extent of geocryological activity in southern Africa, valley asymmetry, like many other aspects of periglacial geomorphology, is little understood. This study, based primarily on analysis of 1:50 000 maps, provides evidence for south-facing slopes having steeper gradients than north-facing slopes in the high Drakensberg region of southern Africa. The fact that periglacial features are active today at high altitudes provides evidence for the hypothesis that this asymmetry could, at least partially, have resulted from former periglacial processes during the cooler climate of the Pleistocene. -Author
Article
Near-surface ground thermal conditions are a delayed response to changing air temperature and may result in needle ice development when air temperatures are above 0 °C and ground temperatures below 0 °C. It is difficult, therefore, to predict needle ice development based only on climatological data. Observations indicate that temporally restricted growth phases produce shorter needle ice lengths than longer growth phases. Copyright © 2001 John Wiley & Sons, Ltd.RÉSUMÉLes conditions thermiques proches de la surface du sol évoluent avec retard après un changement de la température de l'air, aussi des pipkrakes peuvent se développer quand la température de l'air est supérieure à 0 °C et que la température du sol est inférieure à 0 °C. Il est difficile, en conséquence, de prédire le développement des pipkrakes d'après les seules données climatologiques. Des observations indiquent que de courtes phases de croissance produisent des pipkrakes de longueur plus réduite que des phases de croissance de plus grande durée. Copyright © 2001 John Wiley & Sons, Ltd.
Article
The Lesotho Highlands contain some of the highest mountains in southern Africa and play an important role in the surface water resources of the region. Several features of the climatology and hydrology of the highlands are reviewed here. The emphasis is on the long-term response and the behaviour on an annual basis. Topics discussed include the variations in rainfall with elevation and location, the relationships between annual rainfall and river flows, and the variations over time in both rainfall and flow records. Results are presented in the form of updated versions of the mean annual precipitation and mean runoff coefficient maps for the region, and examples are presented for typical regression relationships between flows and rainfall data on an annual basis. Also, statistical analyses are described that suggest little evidence for any significant cyclical behaviour or trend during the observational periods for either rainfall or flow data. © 1998 Royal Meteorological Society
Article
Soil moisture distributions on an instrumented hillslope at Slapton, South Devon, are compared to two topographic indices. The index a/s has been used in a computer runoff model to predict the location of zones of surface saturation on a hillslope (Beven & Kirkby, 1979), whilst the index plan curvature is derived from techniques of terrain analysis using gridded altitude data (Evans, 1980). Neither index is entirely satisfactory for predicting the changing pattern of soil moisture on the hillslope; a combined index proved most appropriate, but only at times of high soil wetness. The potential value of topographic indices as a basis for the prediction of soil moisture distributions and hillslope runoff is briefly discussed.
Article
Spatial patterns in surface soil moisture during dry and wet weather conditions have been recorded over a 3.68 ha gully catchment in central Spain. During dry weather conditions this spatial pattern was characterised by areas of relatively wet and dry soil, forming a mosaic of areas with contrasting hydrological response. Semi-variogram analysis has indicated that these areas are spatially isolated and unconnected, with the effect that surface runoff from source areas within the catchment may be re-absorbed by surrounding areas which act as sinks for overland flow. Consequently during dry weather conditions, variation in the soil's physical and hydrological properties, as reflected by spatial differences in soil moisture, may be advantageous in minimising widespread catchment runoff and erosion, by creating spatial isolation of runoff producing areas and by promoting discontinuity in hydrological pathways. During wet weather conditions, however, extensive saturation, exceeding a catchment wetness threshold, increased spatial continuity in hydrological pathways, regardless of the spatial variation in soil hydraulic properties, resulting in widespread runoff and erosion. Management strategies should therefore aim to raise this wetness threshold value, by improving the soils physical and hydrological properties. The creation of a mosaic pattern of areas with contrasting hydrological response may prove to be an effective management strategy in runoff and erosion control in semi-arid environments.
Article
Surface soil moisture content is a state variable that is either simulated or required as input for many hydrologic models. In distributed hydrologic modeling, the watershed system is subdivided into spatial elements that should be as homogeneous in hydrologic response as possible. In this study, the variation of surface soil moisture was examined because soil moisture is a major factor in determining hydrologic response. The influence of variations in land cover, soil properties and topography on surface soil moisture was investigated. Statistical analysis showed that topography was the most important factor controlling the distribution of soil moisture within the small agricultural watersheds at Chickasha, Oklahoma. The presence of vegetation tends to diminish the soil moisture variations caused by topography, while the effects of minor variations in soil type were usually insignificant. Comparison of variograms developed for nearly flat cropland water-sheds and more sloping rangeland watersheds indicated that a much denser network of sampling points would be required to develop soil moisture maps of a given accuracy on the rangeland watersheds. For many modeling purposes, the subdivision of low-slope cropland watersheds into spatial units of homogeneous hydrologic response can be based on topography alone.
Article
Examples are presented from two locations in SE and NE Spain where patterned or banded vegetation are found on semi-natural and abandoned land or where vegetation is recovering from wildfire. In both cases patterns are being investigated as process-pattern phenomena with the aim of understanding how different kinds of environmental gradients influence pattern evolution. On abandoned land, patterns occur at different scales. At the patch scale there are areas where Plantago albicans germinates in cracks and influences the accumulation of silty material. At the slope scale these form elongated steps that create a characteristic micro-topography. At the patch and slope scale Stipa tenacissima tussocks form an hexagonal pattern on level areas where water infiltrates in and around the tussocks. On sloping areas the S. tenacissima tussocks form parallel ovoid bands. They intercept fine and coarse material being eroded on the slopes by both overland flow and the hooves of sheep and goats. This also creates a distinctive micro-topography. Rainfall simulation experiments were undertaken in combination with monitoring activities in order to investigate the effects that key-processes of sediment and water movement have on the patterns. Other methods include controlled experiments and modelling. Biologically driven erosion processes are very important as key processes. Positive feedback mechanisms are important at various stages in the evolution of the pattern. The patterns studied play an important role in creating more favourable micro-environments where vegetation recovers first after disturbances. This is particularly the case following wildfire. The first post-fire rain produces patterns in ash and litter around sites, concentrating these at locations where shrubby vegetation subsequently resprouts or becomes seeded. On abandoned land, the evolution of patterns reflects the parent material, grazing and the climate.
Article
Gauging data are available from numerous streams throughout Australia, and these data provide a basis for historical analysis of geomorphic change in stream channels in response to both natural phenomena and human activities. We present a simple method for analysis of these data, and a briefcase study of an application to channel change in the Tully River, in the humid tropics of north Queensland. The analysis suggests that this channel has narrowed and deepened, rather than aggraded: channel aggradation was expected, given the intensification of land use in the catchment, upstream of the gauging station. Limitations of the method relate to the time periods over which stream gauging occurred; the spatial patterns of stream gauging sites; the quality and consistency of data collection; and the availability of concurrent land-use histories on which to base the interpretation of the channel changes.
Article
Thesis--University of Natal. Includes bibliographical references (p. 144-146).
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