Arid Namibia Research Articles

Domestication of Marama Bean in Arid Namibia: Challenges and Opportunities in a Climate Changing Agroecology

Domestication of Marama Bean in Arid Namibia: Challenges and Opportunities in a Climate Changing Agroecology

Field and acclimated metabolomes of a resurrection plant suggest strong environmental regulation in the extreme end of the species’ range

Plant secondary metabolites are significant mediators of the interactions of plants with their environment. The desiccation tolerant “resurrection plant” Myrothamnus flabellifolia Welw. is distributed throughout southern Africa and is vicariantly separated between arid Namibia and the comparatively mesic South Africa where it is subjected to contrasting climate regimes. Our earlier study indicated that these populations were metabolomically and phylogenetically distinct, leading us to hypothesise that the metabolic signature of the arid-adapted plants from Namibia was environmentally determined. To test this, we profiled the metabolomes of plants from both regions that had been sampled directly in the field (non-acclimated) with those of plants from the same regions that had been long-term acclimated in a greenhouse (acclimated). Long-term acclimation resulted in a convergence of the metabolic profiles of the plants collected from the different regions. However, while the South African plants demonstrated little difference between their acclimated and non-acclimated metabolomes, the metabolomes of the acclimated Namibian samples were distinct from those of the plants sampled in the field in Namibia. Further scrutiny of the metabolite differences between the acclimated and non-acclimated Namibian samples revealed several metabolites that were significantly more abundant in the field samples, and we propose that these might contribute to survival in this region. To further test the metabolomic response from a temporal perspective, we subjected the acclimated plants to short-term high-temperature treatment in climate chambers. However, this treatment had no significant impact on the metabolomes of the plants. Our findings suggest that long-term, rather than short-term, environmental conditions warrant large-scale reprogramming of the metabolome in M. flabellifolia, and that the climate conditions in the more arid region of the species’ range necessitate the production of particular phenolic metabolites.

Ethnographic Upscaling: Exploring and Testing Hypotheses Drawn from In-depth Ethnographic Findings in Spatially Continuous Cases

This article introduces ethnographic upscaling, an innovative procedure to explore and test hypotheses drawn from in-depth ethnographic findings in spatially continuous cases. The approach combines the strength of localized ethnographic descriptions with questionnaire-based regional surveys to study the distribution of ethnographic findings across social groups by comparison. The approach was designed in the Local Institutions in Globalized Societies project. This anthropological long-term research project ran from 2010 to 2019 to explore institutional regimes for managing water in arid Namibia. The article describes how the ethnographic upscaling approach was developed and implemented, discusses some exemplary results, and offers a critical reflection on its shortcomings and potentials.

The Life of Winds: Knowing the Namibian Weather from Someplace and from Noplace

ABSTRACTThis article brings the two questions, how and what we know, into a productive dialog to explain the difference between indigenous and scientific environmental knowledge. In the case I explore, scientists and Damara pastoralists (ǂnūkhoen) both relate the arrival of the rains in arid Namibia to the interplay between two winds. However, when it comes to explaining those observations, their accounts could hardly be more different. While Indigenous people understand the arrival of the rains as a play between loving and caring winds, scientists recognize them as a consequence of a shift of the Intertropical Convergence Zone. Building on Heidegger's phenomenology, I explore the relationship between the knower and the known. My main theoretical intervention is to show that Damara people and scientists have distinct ways of encountering the world: from someplace and from noplace. In those encounters, the weather is either enmeshed in forms of use in everyday skilled activity for rural pastoralists, or enframed by technology for scientists. By encountering the weather from someplace and from noplace, the world turns into a different place for each. The engagement with these weather worlds shows how ways of knowing the environment can be multiple, but they are not mutually exclusive. [Indigenous knowledge, weather, phenomenology, ontology, Heidegger]

The recharge process in alluvial strip aquifers in arid Namibia and implication for artificial recharge

Alluvial strip aquifers associated with ephemeral rivers are important groundwater supply sources that sustain numerous settlements and ecological systems in arid Namibia. More than 70 % of the population in the nation’s western and southern regions depend on alluvial aquifers associated with ephemeral rivers. Under natural conditions, recharge occurs through infiltration during flood events. Due to the characteristic spatial and temporal variability of rainfall in arid regions, recharge is irregular making the aquifers challenging to manage sustainably and they are often overexploited. This condition is likely to become more acute with increasing water demand and climate change, and artificial recharge has been projected as the apparent means of increasing reliability of supply. The article explores, through a case study and numerical simulation, the processes controlling infiltration, significance of surface water and groundwater losses, and possible artificial recharge options. It is concluded that recharge processes in arid alluvial aquifers differ significantly from those processes in subhumid systems and viability of artificial recharge requires assessment through an understanding of the natural recharge process and losses from the aquifer. It is also established that in arid-region catchments, infiltration through the streambed occurs at rates dependent on factors such as antecedent conditions, flow rate, flow duration, channel morphology, and sediment texture and composition. The study provides an important reference for sustainable management of alluvial aquifer systems in similar regions.

Science education for sustainable development: the Gobabeb experience

Science education and outreach for sustainable development in arid Namibia encompasses a wide range of topics referring to economic, social and environmental issues. This paper reviews selected programmes implemented at Gobabeb over the past several decades as case studies in effective and innovative education and outreach. Programmes at Gobabeb contribute to testing approaches to capacity building – enhanced knowledge, skills and attitudes – over a wide front.

Provenance versus weathering control on the composition of tropical river mud (southern Africa)

This study presents an integrated mineralogical–geochemical database on fine-grained sediments transported by all major rivers of southern Africa, including the Zambezi, Okavango, Limpopo, Olifants, Orange and Kunene. Clay mineralogy, bulk geochemistry, Sr and Nd isotopic signatures of river mud, considered a proxy of suspended load, are used to investigate the influence of source-rock lithology and weathering intensity on the composition of clay and silt produced in subequatorial to subtropical latitudes.Depletion in mobile alkali and alkaline-earth metals, minor in arid Namibia, is strong in the Okavango, Kwando and Upper Zambezi catchments, where recycling is also extensive. Element removal is most significant for Na, and to a lesser extent for Sr. Depletion in K, Ca and other elements, negligible in Namibia, is moderate elsewhere. The most widespread clay minerals are smectite, dominant in muds derived from Karoo or Etendeka flood basalts, or illite and chlorite, dominant in muds derived from metasedimentary rocks of the Damara Orogen or Zimbabwe Craton. Kaolinite represents 30–40% of clay minerals only in Okavango and Upper Zambezi sediments sourced in humid subequatorial Angola and Zambia. After subtracting the effects of recycling and of local accumulation of authigenic carbonates in soils, the regional distribution of clay minerals and chemical indices consistently reflect weathering intensity primarily controlled by climate.Bulk geochemistry identifies most clearly volcaniclastic sediments and mafic sources in general, but cannot discriminate the other sources of detritus in detail. Instead, Sr and Nd isotopic fingerprints are insensitive to weathering, and thus mirror faithfully the tectonic structure of the southern African continent. Isotopic tools thus represent a much firmer basis than bulk geochemistry or clay mineralogy in the provenance study of mudrocks.

A dragonfly in the desert: genetic pathways of the widespread Trithemis arteriosa (Odonata: Libellulidae) suggest male-biased dispersal

Water-dependent species inhabiting desert regions seem to be a contradiction in terms. Nevertheless, many species have evolved survival strategies for arid conditions. In Odonates (dragonflies and damselflies), both larvae and adults require very different and complex water-associated habitat conditions. The present study investigates the genetic diversity, population structure and dispersal patterns of a desert inhabiting odonate species, the Red-veined Dropwing dragonfly, Trithemis arteriosa. Eight populations from the arid Namibia and four population sites in the more tropical Kenya were compared by using nine microsatellite loci, one non-coding nuclear fragment and the mtDNA fragment ND1. Microsatellite analyses as well as the nuclear fragment reveal a high allelic diversity in all populations with almost no genetic sub-structuring. In contrast, ND1 sequence analyses show sub-structuring and—with two exceptions—only private haplotypes. The conflicting patterns of nuclear versus mitochondrial markers suggest a male-biased dispersal in this species. Results indicate that male dispersal is dependent on the environmental stability of the habitat, while females are philopatric. This life history adaptation would allow females to save energy for mating and oviposition in the demanding environment of a desert region. The results give direct insights into the dispersal pathways of a desert-inhabiting, strongly water dependent flying insect.

Exploring consensus in 21st century projections of climatically suitable areas for African vertebrates

Africa is predicted to be highly vulnerable to 21st century climatic changes. Assessing the impacts of these changes on Africa's biodiversity is, however, plagued by uncertainties, and markedly different results can be obtained from alternative bioclimatic envelope models or future climate projections. Using an ensemble forecasting framework, we examine projections of future shifts in climatic suitability, and their methodological uncertainties, for over 2500 species of mammals, birds, amphibians and snakes in sub-Saharan Africa. To summarize a priori the variability in the ensemble of 17 general circulation models, we introduce a consensus methodology that combines co-varying models. Thus, we quantify and map the relative contribution to uncertainty of seven bioclimatic envelope models, three multi-model climate projections and three emissions scenarios, and explore the resulting variability in species turnover estimates. We show that bioclimatic envelope models contribute most to variability, particularly in projected novel climatic conditions over Sahelian and southern Saharan Africa. To summarize agreements among projections from the bioclimatic envelope models we compare five consensus methodologies, which generally increase or retain projection accuracy and provide consistent estimates of species turnover. Variability from emissions scenarios increases towards late-century and affects southern regions of high species turnover centred in arid Namibia. Twofold differences in median species turnover across the study area emerge among alternative climate projections and emissions scenarios. Our ensemble of projections underscores the potential bias when using a single algorithm or climate projection for Africa, and provides a cautious first approximation of the potential exposure of sub-Saharan African vertebrates to climatic changes. The future use and further development of bioclimatic envelope modelling will hinge on the interpretation of results in the light of methodological as well as biological uncertainties. Here, we provide a framework to address methodological uncertainties and contextualize results.

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

The regeneration potential of grazing-affected Nama Karoo vegetation was evaluated by comparing soil seed banks of different microsites across a fence-line contrast in arid Namibia. Seed banks under low and high grazing pressure reflected the condition of the standing vegetation in terms of composition, community structure and species abundance distributions. However, a close concordance between vegetation and seed bank was restricted to the herbaceous and grassy vegetation within the inter-shrub matrix. The divergence of seed bank communities across the fence-line was low at community level but high at the level of species abundances. Continuous severe grazing increased the abundance of small-seeded, prostrate forbs with round seeds and favored unpalatable, annual grasses over palatable, perennial grasses. Microsites provided a source of small-scale variation in seed bank community composition and were dissimilar between the rangelands. Results indicated an advanced divergence in the vegetation at the degraded site with seed banks of species common under sustainable grazing being drastically reduced. Their low abundance, even in safe sites, suggests that long-distance dispersal is one of the main limiting factors for natural re-establishment after disturbance. The inertia in recovery of Namibian degraded rangelands through seed limitation can be overcome only by active species introduction.

Characteristics of the Vegetational Landscape in Mopane Vegetation, Arid Namibia

Characteristics of the Vegetational Landscape in Mopane Vegetation, Arid Namibia

Spatio-temporal variation in soil seed banks under contrasting grazing regimes following low and high seasonal rainfall in arid Namibia

In arid rangelands, soil seed bank characteristics vary with rainfall patterns, livestock pressure and habitat heterogeneity. We investigated this issue by assessing spatio-temporal patterns in soil seed bank density and richness in a degraded (heavy grazing) and non-degraded (light grazing) Nama Karoo ecosystem. To account for variation in seed distribution, different microsites were compared, and the effect of diaspore size on the patterning analyzed. Long-term heavy grazing increased seed densities and species richness of the soil seed bank by favoring small-seeded and tiny-seeded annual species. The spatial patterning of the soil seed bank was, however, similar to that found under sustainable grazing. The overall seed distribution was dictated by the small-scale environmental heterogeneity, which interacted with diaspore size. Our results suggest that the degraded environment is still efficient in controlling secondary dispersal and retaining seeds. This is through low stature barriers like surface rocks, which replace the function of grazing-sensitive perennial grasses in trapping and storing small diaspores. Soil seed banks were persistent and accumulated readily-germinable seeds over time. Observed temporal pattern across the study sites indicates that both condition and sequence of preceding rainfall seasons are likely to have a profound effect on soil seed banks of subsequent years.

How to enter a desert—patterns of Odonata colonisation of arid Namibia

Abstract With a total of 75 species the odonate diversity in the Namibian desert is surprisingly high. Based on their distribution characteristics, invasion patterns, and breeding success, there are six well-defined categories of Odonata: widespread species - (1) permanently living in the desert, and desert biased, (2) permanently living in the desert, but not desert-biased; (3) entering the desert seasonally; (4) entering from neighbouring tropical or temperate regions, whose populations may breed in the desert sometimes or locally. Category (5) consists of species with highly localised breeding populations in the desert, which are widely isolated from potential source populations. The last category (6) consists of species restricted to allochthonous perennial rivers. We discuss these patterns from a geographical and a temporal perspective. On the one hand, there have been different spatial directions from where species have entered deserts. On the other hand, Odonate distribution patterns in the deserts...

Middle-to late-Holocene moisture changes in the desert of northwest Namibia derived from fossil hyrax dung pollen

New pollen results and radiocarbon dating from fossil hyrax middens derived from the edge of the northern Namib Desert address the shortage of continental palaeobotanical evidence in arid Namibia by providing evidence for the environmental conditions during the mid to late Holocene in the region. The results obtained reflect long-term stability in the area throughout most of the sequence. Higher than modern moisture availability is suggested between c. 6 and 1 ka BP by the increased abundance of Poaceae, Cyperaceae or Chenopodiaceae, which respond rapidly by flowering after modest quantities of rainfall. Around 1 ka and recently arid conditions seem to have prevailed, with a decrease in Poaceae and an increase in Acanthaceae. Other palaeoecological evidence from the local and regional surroundings that focused on fluvial deposits, marine palynology and mineralogy confirms this mid-Holocene increase in more effective rainfall.

A regional coupled surface water/groundwater model of the Okavango Delta, Botswana

In the endorheic Okavango River system in southern Africa a balance between human and environmental water demands has to be achieved. The runoff generated in the humid tropical highlands of Angola flows through arid Namibia and Botswana before forming a large inland delta and eventually being consumed by evapotranspiration. With an approximate size of about 30,000 km2, the Okavango Delta is the world's largest site protected under the convention on wetlands of international importance, signed in 1971 in Ramsar, Iran. The extended wetlands of the Okavango Delta, which sustain a rich ecology, spectacular wildlife, and a first‐class tourism infrastructure, depend on the combined effect of the highly seasonal runoff in the Okavango River and variable local climate. The annual fluctuations in the inflow are transformed into vast areas of seasonally inundated floodplains. Water abstraction and reservoir building in the upstream countries are expected to reduce and/or redistribute the available flows for the Okavango Delta ecosystem. To study the impacts of upstream and local interventions, a large‐scale (1 km2 grid), coupled surface water/groundwater model has been developed. It is composed of a surface water flow component based on the diffusive wave approximation of the Saint‐Venant equations, a groundwater component, and a relatively simple vadose zone component for calculating the net water exchange between land and atmosphere. The numerical scheme is based on the groundwater simulation software MODFLOW‐96. Since the primary model output is the spatiotemporal distribution of flooded areas and since hydrologic data on the large and inaccessible floodplains and tributaries are sparse and unreliable, the model was not calibrated with point hydrographs but with a time series of flooding patterns derived from satellite imagery (NOAA advanced very high resolution radiometer). Scenarios were designed to study major upstream and local interventions and their expected impacts in the Delta. The scenarios' results can help decision makers strike a balance between environmental and human water demands in the basin.

The suitability of the degradation gradient method in arid Namibia

AbstractThe Degradation Gradient Method (DGM) is a sophisticated technique for the assessment of range condition. It applies multivariate analyses of herbaceous species data to detect subtle degrees of overgrazing. The suitability of this multivariate method was tested in the central Highland Savanna of Namibia by comparing its results against a univariate analysis of herbaceous data in a simple but robust Range‐Unit Model. Despite aridity and topographical heterogeneity, the DGM performed unexpectedly well under these conditions. The relative instability of this dry savanna system favoured the applicability of the DGM by promoting a clear grazing gradient. Using species density data only resulted in an incorrect outcome of the multivariate analysis. The sensitivity of the DGM could be improved by combining density and cover data.

Range management systems in arid Namibia—what can livestock numbers tell us?

This paper set out to analyse time-series and spatial livestock data in the arid west of Namibia over a period of 11 years. These were interpreted in the context of rainfall conditions and access to water points and encompass communally and commercially managed rangelands. The study showed that stock densities maintained by both, communal and commercial farmers, were remarkably lower than estimated national-level carrying capacities for these rangelands. In the arid communal areas (50–100 mm annual rain), these hovered on average around 1 kg ha −1, increasing to 4 kg ha −1 at 100–200 mm rain and to 8 kg ha −1 in the 200–300 mm annual rain bracket in commercial areas. Stock densities showed no statistical correlation to annual rainfall, but grazer–browser ratio did in communal areas. Although the spatial analysis showed shortcomings, some general trends—to be considered hypotheses for further testing—were evident in these arid rangelands: • Available grazing rather than access to water appeared to limit stock densities, particularly in the drier areas, since the number of water points was not statistically correlated with stock density. • Overall, stock densities in commercial areas were less affected by annual rainfall over the observed period than in the communal areas. • A shorter-term response to annual rainfall was indicated in the communal areas, compared to the commercial farming areas. This indicates that communal farmers adopted an opportunistic management strategy and effectively rested rangelands after a below-average rain year by reducing stock densities. • The shorter-term response strategy was also reflected in greater changes in grazer–browser ratio over time in the communal areas. • Equally, shorter-term responses followed a good season in communal areas by an increase in livestock numbers. • This shorter-term response strategy in communal areas could result in high stock densities coinciding with a poor rainy season, if a good season and the parallel increase in stock densities, is immediately followed by a poor season.

Spatio-temporal rainfall variation and stock management in arid Namibia

Abstract The high inherent variability in rainfall and forage availability in arid regions makes it very difficult for a rancher to establish a herd size that is suited to the environment and also complicates management decision-making regarding the distribution of animals within and between areas of a single ranch. We recorded the temporal and spatial variability in rainfall and grass production on a local scale on 3 ranches in arid Namibia over 3 years, to determine their effects on potential stocking density, stock movement decisions and timing of grazing. We conducted a 3-year experiment to test the effects of the timing of grazing on grass regrowth. Furthermore, we tested the reliability of a rule-of-thumb used by ranchers to ascertain whether a drought year is likely and whether they should sell some of their cattle in advance of drought. We expanded the scale of the study to include 31 ranches over a 700 km-long rainfall gradient to determine the reliability of extrapolating conclusions obtained at...

Spatio-temporal rainfall variation and stock management in arid Namibia

The high inherent variability in rainfall and forage availability in arid regions makes it very difficult for a rancher to establish a herd size that is suited to the environment and also complicates management decision-making regarding the distribution of animals within and between areas of a single ranch. We recorded the temporal and spatial variability in rainfall and grass production on a local scale on 3 ranches in arid Namibia over 3 years, to determine their effects on potential stocking density, stock movement decisions and timing of grazing. We conducted a 3-year experiment to test the effects of the timing of grazing on grass regrowth. Furthermore, we tested the reliability of a rule-of-thumb used by ranchers to ascertain whether a drought year is likely and whether they should sell some of their cattle in advance of drought. We expanded the scale of the study to include 31 ranches over a 700 km-long rainfall gradient to determine the reliability of extrapolating conclusions obtained at a local scale to a larger geographic scale. We found that rainfall and grass production varied widely, resulting in recommended stocking densities up to 10-fold smaller than those currently recommended by the Namibian Ministry of Agriculture. We found that there is no optimal spatial or temporal scale of ranch management, and that ranchers could do no better than a simple rule of “move the cattle to wherever there is most grass”. This simple rule's validity was reinforced by the results of our experiment, which showed that there was no significant effect of timing of grazing on grass regrowth. Statistical analyses of long-term rainfall records indicated that the ranchers' rule-of-thumb regarding approaching drought was unreliable and that this could lead to substantial loss of profit if adhered to.

Wassernutzungskonflikte am Okawango: Szenarios als Entscheidungshilfe

The Okavango River system poses a water resources management problem of outstanding complexity. The runoff generated in the humid Angolan highlands flows through arid Namibia and Botswana before forming a spectacular inland Delta where the water of the Okavango River is completely consumed by evapotranspiration. The high ecological value of the Okavango Delta and its attractiveness to tourists depend on the amount of runoff in the Okavango River and its seasonality. Water abstraction and dam building in the upstream countries are expected to greatly effect the Okavango Delta. To study the impacts of upstream and local interventions as well as to gain a solid quantitative understanding of the different processes acting in the Okavango Delta, a large-scale, coupled surface water/groundwater model has been developed. Because the main emphasis is placed on reproducing the extent of the flooded area in the Delta, the model was not calibrated with point hydrographs but with a time series of two-dimensional flooding patterns derived from satellite imagery. Scenarios were designed to study major interventions and their expected impacts. These results can assist decision-makers in all the affected countries to reach an acceptable compromise between the needs of man and nature in this particularly intricate case.