Top > African Study Monographs > ASM Supplementary Issue Back Number > No.40 (2010)
Historical Change and its Problem on the Relationship between Natural Environments and Human Activities in Southern Africa

Edited by Kazuharu MIZUNO



Kazuharu MIZUNO

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pp. 3-18

Environmental Change and Vegetation Succession along an Ephemeral River: The Kuiseb in the Namib Desert

Kazuharu MIZUNO
Graduate School of Asian and African Area Studies, Kyoto University

     Forests line the course of the Kuiseb River, an ephemeral river in the Namib Desert, and several areas of these forests are characterized by high concentrations of tree death (Mizuno, 2005; Mizuno & Yamagata, 2005). We sought to clarify the relationship between recent environmental changes and such tree deaths in the region. In November 2007, we examined the roots of a seedling of Acacia erioloba that was germinated by rainfall beginning in January 2006. The Acacia erioloba had grown to a height of 10cm and its roots to over 230cm, within two years. In the sapling (seedling) stage, Acacia erioloba extends its main roots deeply until it reaches a moist, fine-grained soil layer (sandy silt) and can absorb water through lateral roots. When it reaches the stage at which the water supply from the moist, fine-grained soil layer is insufficient for its growing size, the tree extends innumerable lateral roots within a 50cm depth from the land surface, where they absorb water that has been transported to a shallow depth by fog and other sources. Acacia erioloba dies when its lateral roots are unable to absorb water. Until the mid-1970s, successive floods repeatedly deposited fine-grained materials (e.g., sandy silt) that create water-bearing sediments for the growth of Acacia erioloba, and the trees died only rarely. However, from 1980 to 1985 these materials became increasingly scarce due to the decreasing occurrence of flooding, and consequently many trees died. It is reasonable to infer that the trees died because fine sediments were no longer being regularly deposited, and because of the drawdown of the groundwater level, both of which are making it difficult for the shallow roots of the trees to absorb the water necessary to survive.

Key Words: Environmental change; Vegetation succession; Tree death; Flooding; Sand dune.

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pp. 19-30

Recent Grain-Size Coarsening of Floodplain Deposits and Forest Decline along the Kuiseb River, Namib Desert, Namibia

Division of Social Studies, Joetsu University of Education

    We investigated the flood plain deposits of the middle reach of the Kuiseb River in order to reveal the recent fluvial environment changes and forest decline. For the conservation of watershed environments, it is important to examine the relationship between environmental and hydrological changes. Fluvial deposits are useful for this as they record the past environmental changes in a catchment. Grain size coarsening was seen in the upper flood plain deposits in many places. The cause of the deposit coarsening was considered to be a relative increase in the supply of coarse material. The frequency of floods seems to have been decreased by the construction of many dams in the upper stream area, but sand dunes continue to advance on the river bed, increasing the relative supply rate of coarse material (dune sand). Notable forest declines were observed at the places where marked deposition of coarse sand had occurred, as such coarse deposits cannot retain water and are desiccated rapidly. The subsequent severe dry conditions at the roots induce tree death.

Key Words: Namib Desert; Kuiseb River; Riparian forest decline; Grain size coarsening; Flood plain deposit; Dam construction.

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pp. 31-50

Soil Clay Minerals in Namibia and their Significance for the Terrestrial and Marine Past Global Change Research

Institute of Geography, Universität Regensburg
Research Department of Ecology and Ecosystem Sciences,
Technische Universität München

    We delineated seven soil clay mineral provinces in Namibia. Many individual clay mineral assemblages occur in fluvial, pan, cave and other environments. Previous researchers have used clay mineral compositions as evidence for palaeoenvironmental reconstructions, often without analyzing the formation, the transport and the deposition of these clay minerals. In Namibia, rates of erosion and denudation by water and wind have been very small since early Quaternary times. During the Quaternary, the clay mineral assemblages of the seven provinces and of individual clay mineral deposits did not change significantly. Palaeoenvironmental reconstructions have to consider these small rates of erosion, especially if clay minerals were transported by water and/or wind from their source area to distant regions (e.g., the ocean). Changes in marine clay mineral compositions may not reflect climate change, but can be caused by changes in the ratio of fluvial to aeolian transport. If the changes in the transport mode are known, these changes can be interpreted palaeoenvironmentally. Future researchers have to decipher quantity and quality of the fluvial and aeolian dust transport (clay minerals, pollen, etc.) over southwestern Africa and the Benguela Current area.

Key Words: Namibia; Clay minerals; Terrestrial and marine geoarchives; Quaternary palaeoclimate.

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pp. 51-66

Late Pleistocene Sedimentary Environment of the “Homeb Silts” Deposits, along the Middle Kuiseb River in the Namib Desert, Namibia

Cultural History and Geoscience Research Group, Science Research Department, Lake Biwa Museum

    In the Namib, the tectonic and geographic setting of the area means that there are no large lake basins, and relict aeolian deposits appear to be quite rare. This has posed severe problems for reconstructing palaeoclimates in this region. In addition, there are significant problems with developing a well-dated chronology of events, as well as in the interpretation of the dated evidence for hydrologic and climatic changes. The Late Pleistocene “Homeb Silts” have been interpreted in previous studies as follows: (1) dunedamed lake sediments indicating an arid environment; (2) river end-point deposits indicating arid conditions; (3) flood plain sediments of an aggrading river indicating a semi-arid environment and (4) river flood slack water sediments indicating a wet environment and intense precipitation events in the headwaters. In this present study, sedimentary facies of the “Homeb Silts” were re-described and interpretation of the sedimentary environment changes that resulted in their deposition re-assessed. The conclusions are as follows: (1) The “Homeb Silts” were deposited during ca. 26 to 19 k yrs BP (ca. 25 to 19 k cal yrs BP) as indicated by eleven AMS 14C measurements; (2) Almost all of the “Homeb Silts” were deposited under wet conditions by fluvial floods, except during the early depositional phase; (3) The “Homeb Silts” have recorded some detailed environmental changes during ca. 26 to 19 k yrs BP (ca. 25 to 19 k cal yrs BP); and, (4) Depositional events caused by similar climatic events in recent years have occurred, like heavy rains and flood events in the headwaters.

Key Words: Namib Desert; Kuiseb River; Slack water sediments; Sedimentary environment; Last Glacial Maximum (LGM); AMS radiocarbon dating; Palaeohydrology.

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pp. 67-76

Seasonal Trends of Rainfall and Surface Temperature over Southern Africa

Department of Geography, College of Humanities and Sciences, Nihon University
Tokyo Metropolitan Research Institute for Environmental Protection

    This study investigated seasonal trends of surface temperature and rainfall from 1979 to 2007 in southern Africa. In recent years, annual rainfall has decreased over the African continent from the equator to 20ºS, as well as in Madagascar. On the other hand, annual mean surface temperature has shown an increasing trend across the whole region, with particularly large rates of increase in Namibia and Angola. The spatial and temporal structures of trends in rainfall and surface temperature have apparent seasonality, with rainfall in Angola, Zambia, and Namibia tending to decrease from December to March, and surface temperature from Namibia to southeastern South Africa tending to increase from July to October. To clarify the relationship between the seasonal trend and the interannual variation of the seasonal march of rainfall, empirical orthogonal function (EOF) analysis was applied to pentad rainfall data. The first and second modes of temporal structures showed strong seasonality, and their seasonal marches modulated after 1987 and 1995, respectively. These modulations included delay in rainy season onset, early withdrawal of the rainy season, and weak rainfall.

Key Words: Seasonal trend; Rainfall; Surface temperature; Seasonal march; Modulation.

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pp. 77-89

Vegetation structure of the biomes in southwestern Africa And their precipitation patterns

Graduate School of Horticulture, Chiba University

    Southwestern Africa contains diverse biomes. The amount of the annual precipitation of this area has been traditionally thought to be the most important controlling factor to the differentiation of the biomes. However, this territory experiences the summer rain type and winter rain type. Those two different precipitation patterns should result in the different mechanisms to control the distribution of the biomes. This study intends to clarify the relationships between the distribution of the biomes and the summer rain type and winter rain type, knowing the vegetation structure in terms of the growth forms of the dominant plants. Studies were conducted in the area southwestern Africa, including major biomes of the southern Africa. Grassland, Nama-karoo and Savanna appear in the area with the summer rain type. Both of Succulent karoo and Fynbos appear in the area with the winter precipitation type. The amount of winter precipitation of those two biomes is much higher than that of the other tree biomes. This higher amount of winter precipitation encourages the dominance of evergreen woods and succulents in those two biomes. Especially the succulents efficiently utilize the winter precipitation. This leads to the dominance of the succulents on those two biomes.

Key Words: Deciduous shrub; Grassland; Savanna; Succulents; Summer rain; Winter rain.

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pp. 91-102

Monitoring tenebrionid beetle biodiversity in Namibia

Joh R. HEN SCHEL1, Constanze GRO HMANN2, Veronica SITE KETA3, K. Eduard LIN SEN MAIR4

1,3Gobabeb Training and Research Centre
2,4Department of Animal Ecology and Tropical Biology, Biocentre, University of Würzburg

    Different field methods of determining abundance and species diversity of darkling beetles (Coleoptera, Tenebrionidae) were tested. A combination of the use of pitfall traps and linear transect surveys served as the best rapid assessment of diversity, while pitfall traps alone are good for estimating abundance. Trap size (15cm diameter vs. 10cm diameter) and different degrees of exposure to sun did not significantly affect the capture rate of beetles, which was highly variable between traps at a site, but there were differences between sites and seasons. A minimum of a full year of trapping is required before the slope of the species-effort curve begins to flatten when the most abundant species have been recorded. The curve continues to increase over the course of the next 20 years, by which time all species at a location have been recorded. Furthermore, long trapping periods covers different climatic conditions, reflecting that in the Namib Desert, long-term records are required to study biodiversity.

Key Words: Namib Desert; Darkling beetles; Pitfall traps; Trap size; Species-effort curve.

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pp. 103-114

Influence of Geomorphology on the Physiognomy of Colophospermum mopane and its Effect on Browsing in Central Namibia

Graduate School of Asian and African Area Studies, Kyoto University

    Colophospermum mopane is a characteristic tree species indigenous to Southern Africa, where it forms ‘mopane vegetation.’ Mopane plays an important role in livestock farming, and the physiognomy of mopane influences the availability of feed. This study clarified the relationship between the difference in mopane physiognomy and the browsing activity of goats with reference to geomorphology. The physiognomy of mopane corresponded to geomorphological characteristics of surface structures and soil layer thickness. Consequently, the landscape based on the physiognomy of mopane was more diverse in the mountainous study area. Short, multi-stemmed mopane dominated the pediment and crest surface, while tall, single-stemmed mopane trees dominated the flood plain and ephemeral river bed. We determined that people recognize the differences in vegetation and geomorphology and use this knowledge to ensure good browsing for their goats. Most browsing occurred on pediment, where many short, multi-stemmed mopane plants, an important browsing resource for goats, can be found. The physiognomy of mopane at the study site corresponded to geomorphology and was related to browsing activity.

Key Words: Colophospermum mopane; Tree shape; Land unit; Browsing activity; Feed resource; Namibia.

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pp. 115-128

Interactions between Termite Mounds, Trees, and the Zemba People in the Mopane Savanna in Northwestern Namibia

Graduate School of Asian and African Area Studies, Kyoto University

    Termite mounds comprise a significant part of the landscape in northwestern Namibia. The vegetation type in this area is mopane vegetation, a vegetation type unique to southern Africa. In the area where I conducted research, almost all termite mounds coexisted with trees, of which 80% were mopane. The rate at which trees withered was higher on the termite mounds than outside them, and few saplings, seedlings, or grasses grew on the mounds, indicating that termite mounds could cause trees to wither and suppress the growth of plants. However, even though termite mounds appeared to have a negative impact on vegetation, they could actually have positive effects on the growth of mopane vegetation. Moreover, local people use the soil of termite mounds as construction material, and this utilization may have an effect on vegetation change if they are removing the mounds that are inhospitable for the growth of plants. Consequently, both termite mounds and human activities should be taken into account as factors affecting mopane vegetation.

Key Words: Mopane vegetation; Termite mounds; Utilization of termite mounds; Vegetation change.

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pp. 129-154

Changes in Natural Resource Use among Owambo Agro- Pastoralists of North-Central Namibia Resulting From The Enclosure of Local Frontiers

Yuichiro FUJIOKA
Graduate School of Asian and African Area Studies, Kyoto University

    Agro-pastoralists living in arid lands of Africa tend to have highly mobile lifestyles and to use natural resources widely and sparsely. Thus, they require frontiers with low population densities and sufficient natural resources. However, this study found that the enclosure of the local frontier has prompted social changes, such as the setting of conservation areas and the construction of new villages. The aim of this study was to clarify how Owambo agro-pastoralists living in north-central Namibia have changed their use of natural resources in response to transformations to the local frontiers they inhabit. The Owambo group consists of a number of subgroups. Some of these groups formed small kingdoms; most group members live at the kingdom’s center surrounded by the frontier at the periphery. Since the 1970s, other people have migrated into these frontier areas and altered the local conditions, forcing inhabitants to change their use of natural resources. Local inhabitants have coped with this situation in three main ways: (1) wealthy people have established private cattle posts in the frontier where they graze their livestock and gather natural resources, (2) some (especially non-wealthy people) have started to use indigenous fruit trees in multiple and intensified ways, not only for their fruit but also as building materials and wood for fuel, and (3) older villagers have established social networks with newer villagers on the frontier to exchange goods that are available only from their respective areas. The progress of people who can access the natural resources in the frontier has been limited by the enclosure of the local frontier. However, local customs involving the reciprocal exchange of surplus natural resources among neighbors and neighboring areas remain and have been adapted in response to the new situation.

Key Words: Frontier; Natural resource use; Intensification; Arid land; Ovambo; Namibia.

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pp. 155-177

Changes in Developmental Trends of Caregiver-Child Interactions among the San: Evidence from the !Xun of Northern Namibia

Graduate School of Asian and African Area Studies, Kyoto University

    The San have been the subject of extensive research with respect to their foraging lifestyle that is assumed to date back to antiquity. I conducted field research among the !Xun San, who have had close associations with the neighboring agro-pastoralists, in order to deepen understanding in this area. As anticipated by previous studies on the influence of sedentarization, !Xun children were increasingly engaged in the care of their younger siblings or cousins. These studies also predicted early weaning from breastfeeding. Indeed, the transition from breastfeeding to solid baby food occurred primarily during the second year after birth, regardless of the mother’s next pregnancy, among the present-day !Xun. However, several findings did not meet the expectations raised by previous studies. Despite the difference in subsistence patterns, the trend toward parity among sedentary !Xun women was quite similar to that of nomadic Ju|’hoan women. The developmental transition involving touching and holding by the mother was similar among the Ju|’hoan and the !Xun. Gymnastic behavior preceding unaided walking of children persisted, even among the sedentary !Xun, mediated by differences in folk knowledge regarding such gymnastic behavior. Based on this evidence, I reconsidered the relationships among ecology and subsistence patterns, parental ideology, and patterns of caregiver-child interactions.

Key Words: Childhood; Hunter-gatherers; Caregiving behavior; Socialization; Adaptation.

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pp. 179-194

The Natural Environment and the Livelihoods of People Living in a Mountainous Region of Lesotho

Graduate School of Asian and African Area Studies, Kyoto University

    Lesotho is a mountainous country in southern Africa where the indigenous people practice both crop cultivation and pastoralism. This paper describes the relationship between the natural environment and the agro-pastoral land use of the region. To precisely clarify the relationship between land use and the natural habitat, the local ecosystems near a village in eastern Lesotho were examined in detail for 6 months. Temperature, soil and landform surveys were conducted. The characteristic landscape of the site was a terrace formation at about 2,500m above sea level. Settlements were located horizontally along the 2,600m contour line, separating the steep slope of the mountain and the gentle slope of the terrace. Three distinct land use patterns, each with unique environmental characteristics, were identified: cultivated fields, pastures, and settlements. In cultivated fields, the types of crops cultivated and the average temperature differed according to location. Pasture areas had the most extreme maximum and minimum temperatures, and minimal soil depths. Settlements were located above a cold-air lake that formed nightly, and here the diurnal range of temperatures was the least, indicating relative comfort in these areas.

Key Words: Mountainious region; Livelihood; Land use; Agro-pastoralism; Lesotho.

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