Top > African Study Monographs > ASM Supplementary Issue Back Number > No.30 (2005)
Studies on the Environmental Change and Human Activities in Semi-Arid Area of Africa

Edited by Kazuharu MIZUNO


pp.1

Preface

Kazuharu MIZUNO

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NAMIB DESERT
pp. 3-14

VEGETATION SUCCESSION AND PLANT USE IN RELATION TO ENVIRONMENTAL CHANGES ALONG THE KUISEB RIVER IN THE NAMIB DESERT

Kazuharu MIZUNO
Graduate School of Asian and African Area Studies, Kyoto University
Kotaro YAMAGATA
Division of Social Studies, Joetsu University of Education

ABSTRACT
   The aim of this study was to clarify the relationship between environmental change and vegetational succession in the Kuiseb River area of the Namib Desert. The results reveal the following: 1. About 5000-7000 years ago, wetter conditions prevailed in the Kuiseb River basin, forming a wider riverbed than at present. 2. About 600 years ago, a low terrace formed. The low terrace was characterized by the growth of acacia trees and other vegetation, which trapped and accreted aeolian sand. 3. About 400 years ago, the trapped and accumulated sand began to form a sand dune, eventually killing the tree population. 4. At the present time, all of the buried acacia trees have died and have been replaced by salvadora bushes, which continue to trap sand and increase the size of the dune. 5. Plants such as Acacia erioloba, Faidherbia albida, and Acanthosicyos horridus are very important food sources and shade plants for the local Topnaar people and their livestock. The succession of vegetation in response to environmental change has a profound impact on life in the Kuiseb River area, owing to the harsh environmental conditions and scarce plant life in the region.

Key Words: Environmental change; Sand dune; Vegetation succession; Kuiseb River; Topnaar people.

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pp. 15-25

LANDFORM DEVELOPMENT ALONG THE MIDDLE COURSE OF THE KUISEB RIVER IN THE NAMIB DESERT, NAMIBIA

Kotaro YAMAGATA
Division of Social Studies, Joetsu University of Education
Kazuharu MIZUNO
Graduate School of Asian and African Area Studies, Kyoto University

ABSTRACT
   The hyperarid to arid Namib Desert extends along the west coast of southern Africa. The Kuiseb River is one of the major ephemeral rivers originating in the interior highland, and crosses the Namib Desert. Fluvial terraces are well developed along the middle reaches of the Kuiseb River near Gobabeb, and are classified into four surfaces: upper (H), middle 1 (M1), middle 2 (M2), and lower (L). Layers of calcrete are founded on the M1 and M2 surfaces, and gypcrete layers are founded on the H surface. Dead tree matter, buried by dune sand on the L surface, dates to 300±60 years BP and 550±50 years BP. The calcareous crusts on the M1 surface date to 5,300±60 years BP and 6,450±50 years BP, and those of the M2 surface date to 22,070±260 years BP. The presence of calcrete suggests that the ground water level was higher when the M1 and M2 surfaces were formed than it is at the present time. Tree size distribution on the L surface demonstrates that the L surface was also formed during a relatively wet period. It may be concluded, therefore, that these fluvial terraces record the humid periods of ca 22 ka, 5-6.5 ka, and 300-600 years BP in the catchment area of the Kuiseb River. The presence of a water-soluble gypsum crust on the H surface suggests that the paleohydrologic environment of these terrace-forming periods probably involved increased rainfall in the interior highland east of the desert.

Key Words: Namib Desert; Kuiseb River; Ephemeral River; Fluvial Terrace; Calcrete, Dendrochronology; Paleohydrology.

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pp. 27-41

ENVIRONMENTAL CHANGES IN RELATION TO TREE DEATH ALONG THE KUISEB RIVER IN THE NAMIB DESERT

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

ABSTRACT
   The Namib Desert is located along the western coast of Namibia and is affected by the cold Benguela Current. Although forest is distributed along the Kuiseb River in the Namib Desert, many trees are almost dead in some areas. The aim of this research was to clarify the relationship between environmental changes and tree death. The results of the survey are summarized as follows: (1) Many dead trees are located on the riverbanks made of dune sand, which are about 1 m high. (2) Dead trees are located in transitional areas where a northward protrusion of the southern shore is followed by a southward protrusion of the northern shore along the course of the river, in proximity to a sand dune. (3) Floods have eroded the noses of advancing sand dunes of the upper stream and have caused tree death by depositing sand. (4) The date of tree death has been estimated between the late 1970s and the early 1980s by 14C dating. (5) Flood days numbered 33 per year from 1962 to 1975 and 2.7 from 1976 to 1985. The remaining thick sand layer, deposited by the last flood, may be the cause of tree death, given that there was drastic decrease in fl oods since 1976. (6) Tree death has greatly affected people's lives along the Kuiseb River because they depend on riverside forests as a source of shade, shelter, fuel, and food for humans and livestock.

Key Words: Kuiseb River; Namib Desert; Tree death; Flood decrease; Sand deposits; Humans.

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pp. 43-56

TEMPORAL AND SPATIAL VARIABILITY OF GRASS PRODUCTIVITY IN THE CENTRAL NAMIB DESERT

Joh R. HENSCHEL
Gobabeb Training & Research Centre
Antje BURKE
Enviroscience
Mary SEELY
Desert Research Foundation of Namibia

ABSTRACT
   The production of grass was investigated on the gravel plains of the Central Namib Desert, Namibia, during 10 rainfall seasons sampled between 1989-2003. The aim was to evaluate the rainfall-productivity relationship, to elucidate the relationship between temporal and spatial variability, and to examine the spatial scale of patchiness. We compared two different methods and found that a less accurate rapid assessment of grass cover correlated well with measurements of biomass. Our data were in agreement with previous determinations of the desert end of the curve of grassland productivity, and productivity was closely related to the rainfall of the particular season. There was high variability between years at study sites, especially in the west (CV=279%), where it rained more seldom than in the east (CV=86%). During all years rainfall was very patchy at a spatial scale of 5 km, which apparently reflected the storm path of individual rain clouds. Long-term monitoring should be continued in order to detect changes of pattern in this rainfall-driven system.

Key Words: Rainfall-productivity relationship; Rapid assessment; Grass biomass; Storm cloud size; Patchy rainfall.

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pp. 57-64

ORIGIN OF THE FOG IN NAMIB DESERT IN DRY SEASON

Keiji KIMURA
Graduate School of Information Science and Technology, Hokkaido University

ABSTRACT
   The origin of the fog in the Namib Desert was generally considered the westerly advection fog over the Benguela cold current. When the author went to the Namib Desert in dry seasons in 2003 and 2004, the fog in the early morning, however, moved easterly from the inland to the Atlantic Ocean. It was the opposite direction of so called the sea fog. In addition to that, the fog in the Namib Desert showed the diurnal change: the fog arises in the early morning and disappeared before noon. The fog was usually driven easterly to the Atlantic Ocean. Through the climatic observation, the following were found for consideration of the origin of the fog on early August, 2004: it is not advection fog but that it is radiation fog. In the daytime, the air which is comparatively moist because of sea breeze moved to the inland, and it is solidified by radiative cooling in the night. Thus, the water vapor runs the fog and it is blown by the land wind to the westward.

Key Words: Radiation fog; Advection fog; Namib Desert; Diurnal change; Observation.

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pp. 65-75

CHANGES IN THE DISTRIBUTION OF THE !NARA PLANT THAT AFFECT THE LIFE OF THE TOPNAAR PEOPLE IN THE LOWER KUISEB RIVER, NAMIB DESERT

Masaaki ITO
Graduate School of Asian and African Area Studies, Kyoto University

ABSTRACT
   The !Nara plant is endemic to the central Namib Desert. The Topnaar people, who live along the Kuiseb River, use this plant in their daily lives, as it serves as a vital source of income, nutrition, and traditional culture. !Nara is virtually the only food source of the Topnaar during harvest time, and cash can be obtained by selling the seeds of the !Nara fruit. In fact, 40% of Topnaar harvesters have no other source of income. A fl ood protection wall was built in 1961 to protect Walvis Bay from flood damage, and a tributary that once flowed to the town was dammed as a result. A large percentage of !Nara was killed, and the crop yield decreased dramatically. The loss of floodwaters following the construction of the wall likely resulted in a decreased moisture supply, causing !Nara vegetation to suffer. It is probably difficult for seeds to germinate owing to the decreased flooding erosion, the increased accumulation of sand, and the lowered groundwater table.

Key Words: !Nara; Topnaar; Namib Desert; Flood; Groundwater.

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pp. 77-88

CHANGE IN POPULATION AND LAND-USE INTENSITIES IN SEVERAL VILLAGES OF THE FOUR NORTHERN REGIONS OF NAMIBIA

Shigeru ARAKI
Graduate School of Asian and African Area Studies, Kyoto University

ABSTRACT
   Demographic changes in several rural areas in the four northern regions of Namibia were traced from 1991 to 2001 using national census data. On average, the population growth rate of the surveyed area was 2.77% per year. Although this rate approximated the country's mean growth rate of 2.64%, the surveyed areas showed significant differences from the mean, ranging from 3.4% to 7.2% per year. A combination of demographic and land use data collected from four representative villages in the study region revealed that rural-to-urban migration on a micro-scale is a significant process in the control of the area's ecology and economy, and that the percentage of cultivated land is closely tied to population density.

Key Words: Namibia; Owamboland; Four northern regions; Population census; Land use intensity.

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pp. 89-105

VEGETATION CHANGES AND USE OF PALMS AS A BUILDING MATERIAL BY OVAMBO AGRO-PASTORALISTS IN NORTH-CENTRAL NAMIBIA

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

ABSTRACT
   This paper focuses on the mutual transition between vegetation and timber use by the Ovambo people in north-central Namibia and their use of palms for timber in recent years. The vegetation around the research area was characterized as Mopane savanna, dominated by Colophospermum mopane. Historically, the Ovambo used mainly Mopane trunks for timber. However, as bush encroachment advanced in some parts of north-central Namibia, residents were forced to collect Mopane timber from the south. Since the 1970s, however, collecting Mopane has become difficult, and the inhabitants have therefore begun to use palm petioles for timber. Because the use of this resource requires many palm petioles, an environment conducive to grow many palms is required to make this option feasible. The vegetation configuration of this environment was formed mainly by three factors: (1) the unique fl ood terrain initially dispersed palm seeds over a wide area, (2) humans involuntarily dispersed seeds after eating, (3) palms were conserved by the residents. Thus, the increased use of palms emerged at a point of intersection between a change in vegetation patterns and a change in plant use by humans. The critical points of this use are its sustainability and the maintenance of traditional building complexity.

Key Words: Ovambo; Palm use; Mopane savanna; Vegetation change; Namibia.

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pp. 107-117

FARMER'S SELECTION OF LOCAL AND IMPROVED PEARL MILLET VARIETIES IN OVAMBOLAND, NORTHERN NAMIBIA

Daisuke UNO
Graduate School of Asian and African Area Studies, Kyoto University

ABSTRACT
   A new and improved cultivar of pearl millet (Pennisetum glaucum), Okashana-1, was released in Namibia in 1990 and was rapidly adopted in Ovamboland. However, as most farmers do not buy new seeds each year, any genetic trials of the cultivar on actual farms would be affected by cross-pollination. The present study clarified the characteristics of Okashana-1, as found on actual farms. In addition, this research also examined the interrelationships between the environmental status, traditions, livelihood, and subsistence activities in the study area and the cultivar characteristics.

Key Words: Okashana-1; Pearl millet; Namibia; Ovamboland.

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pp. 119-133

HOLOCENE CLIMATE OF NAMIBIA: A REVIEW BASED ON GEOARCHIVES

Klaus HEINE
Institute of Geography, University of Regensburg, Germany

ABSTRACT
   The Holocene palaeoclimates in Namibia are reviewed by discussing different palaeoclimate geoarchives. The available evidence suggests little climatic fl uctuations during the Holocene. There is evidence of more humidity compared to today during the early Holocene. Short dry episodes occurred around 8 14C-ka BP and around 5-3 14C-ka BP. Since 1000 years the northern Benguela Current sea surface temperatures show a decline and since ca. 500 years Namibia experienced in the Namib Desert and adjacent areas more arid condi- tions than before. Extreme fl ash floods occurred more frequently during the Little Ice Age, probably correlating to variations of sun spot activity.

Key Words: Holocene; Geoarchives; Palaeoclimate; Namibia.

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pp. 135-151

FACTORS CONTROLLING GEOGRAPHICAL DISTRIBUTION IN SAVANNA VEGETATION IN NAMIBIA

Susumu OKITSU
Faculty of Horticulture, Chiba University

ABSTRACT
   Here, I describe the geographical distribution of the savanna types in Namibia and identify the factors controlling the occurrence of each savanna type in relation to the amount of annual precipitation and the various physiographical regions, including the mopane (Colophospermum mopane) area. The different types of savanna can be distinguished on the basis of the leaf habits of the dominant vegetation: deciduous, evergreen nanophyll, and evergreen notophyll. In general, vegetation performance (i.e., vegetation cover and maximum height) was positively correlated with the amount of annual precipitation. However, the occurrence of a particular savanna type coincided well with physiographical region regardless of the amount of annual precipitation received. Deciduous savanna occurred primarily in the Central Highland and had the smallest total vegetation cover among the three types. The dry soil of this region determined inevitably the deciduous leaf habit of the vegetation during the dry season and thus the smallest total vegetation cover. Evergreen nanophyll savanna was found mainly in the Mega Kalahari, where I observed a clear relationship between the amount of annual precipitation and total vegetation cover. The soil moisture in this region favored an evergreen leaf habit, even in the dry season, resulting in the effective use of soil water throughout the year. This probably accounted for the large increase in total vegetation cover with increasing annual precipitation. Evergreen notophyll savanna exclusively appeared in the mopane area, regardless of the physiographical region, and had the largest total vegetation cover, apparently as a result of the ecological characteristics of mopane. Therefore, it appears that the geographical distribution of the various savanna types in Namibia is principally controlled by two different factors that are independent of the amount of annual precipitation: the water-holding capacity of the soil and the ecological characteristics of mopane.

Key Words: Annual precipitation; Colophospermum mopane; Deciduous tree; Evergreen nanophyll; Evergreen notophyll; Savanna.

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pp. 153-163

OBSERVATION OF RIPARIAN VEGETATION IN WESTERN NAMIBIA BY USING NDVI AND NDWI DERIVED FROM SPOT-VEGETATION

Hiroyuki YOSHIDA
Faculty of Policy Management, Keio University

ABSTRACT
   Ephemeral rivers in western Namibia are unique entities that support both natural vegetation and human activities. This paper presents an approach for observing riparian vegetation along them synoptically using remotely sensed datasets, derived from a satellite borne sensor named SPOT-VEGETATION. The most commonly used vegetation index, the Normalized Difference Vegetation Index (NDVI), certainly delineates the overall distribution of vegetation, but not without errors. A vegetation index that was designed as a supplement for NDVI, the Normalized Difference Water Index (NDWI), showed some interesting features, but again, with faults. By synthesizing the two indices, the scarce and sparse vegetation in coastal deserts and the relatively dense vegetation in inland highlands could be effi ciently observed. Furthermore, by introducing a fl ow accumulation model produced from a digital elevation model (DEM), it became possible to observe such riparian vegetation quantitatively and systematically.

Key Words: Riparian vegetation; Ephemeral rivers; Flow accumulation model; Namibia; Normalized Difference Vegetation Index; Normalized Difference Water Index; SPOTVEGETATION.

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pp. 165-181

CLIMATE ANOMALIES AND EXTREME EVENTS IN AFRICA IN 2003, INCLUDING HEAVY RAINS AND FLOODS THAT OCCURRED DURING NORTHERN HEMISPHERE SUMMER

Hiroshi KADOMURA
Emeritus Professor, Tokyo Metropolitan University

ABSTRACT
   The climate of 2003, particularly during Northern Hemisphere summer, was marked by exceptionally abnormal events throughout the world, and Africa was no exception. As record heat waves prevailed over Europe, heavy rains and floods occurred over the west-central Sahara, across the Sudano-Sahelian region and western Kenya, while drought conditions gripped the Guinea Coast and southeastern Southern Africa, and cold waves hit southern South Africa. Among the most remarkable events were record rainfall in the western portion of the Sahara-Sahel and drought conditions over the Guinea Coast that were both caused by an extreme northward penetration of the ITCZ relative to normal years. In addition, record-breaking cold weather occurred in southern South Africa in mid-August by a strong extratropical cyclone accompanied by a cold front. During Southern Hemisphere summer, Madagascar, Mozambique, Zimbabwe, and Malawi frequently experienced heavy rains and fl oods associated with tropical cyclones and their remnants. More than 550 people died and over 2.5 million were displaced because of fl oods in Africa in 2003. Africa's vulnerability to climate hazards could be reduced through enhancements of both short- and long-term coping strategies, climate monitoring and early warning systems, flood control infrastructures, and other disaster preparedness measures at all levels, including sub-regional, national, and local levels. Mechanisms that caused various events in Africa in 2003, events which can be viewed as regional responses in Africa to anthropogenic global warming, must be explored from the perspective of global change.

Key Words: Climate anomalies; Extreme events; Heavy rains; Floods; Northern Hemisphere summer 2003.

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pp. 183-193

A VEGETATION-MAINTAINING SYSTEM AS A LIVELIHOOD STRATEGY AMONG THE SEREER, WEST-CENTRAL SENEGAL

Masaaki HIRAI
Graduate School of Asian and African Area Studies, Kyoto University

ABSTRACT
   A fi eld study of the system of maintaining vegetation practiced by the Sereer people was conducted from October 2001 to July 2002 at N village, located in the Thiès Department of west-central Senegal. For centuries, the Sereer people have practiced millet cultivation in combination with livestock raising and have maintained a unique form of artifi cial vegetation, dominated by the tree Acacia albida. The aim of this study was to reveal how the Sereer use and maintain the vegetation. Acacia albida contributes to their livelihood in several ways by functioning, for example, as a green manure and as fodder for livestock. The Sereer deliberately maintain the vegetation through "yar", which means to grow Acacia albida seedlings in cultivated fi elds. A "yar" behavior is one associated with "upbringing" in the Sereer idiom. Use of this tree up to the 1970s helped to make the Sereer livelihood system more secure in an erratic, semi-arid climate.

Key Words: Senegal; Sereer; Acacia albida; Livelihood activities; Vegetation-maintaining system.

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pp. 195-212

EGETATION SUCCESSION IN RELATION TO GLACIAL FLUCTUATION IN THE HIGH MOUNTAINS OF AFRICA

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

ABSTRACT
   Dramatic changes are taking place in the glacier-covered high mountains of Africa. The glacier-covered area on Kilimanjaro is now only half as large as it was in the 1970s. The Tyndall Glacier on Mt. Kenya, which retreated at approx. 3 m yr-1 from 1958 to 1997, retreated at ca. 10 m yr-1 from 1997 to 2002. Pioneer species such as Senecio keniophytum, Arabis alpina, mosses, lichen, and Agrostis trachyphylla have advanced over areas formerly covered by the glacier. The rate at which this vegetation migrated up the former bed of the glacier (2.1 - 4.6 m yr-1 from 1958 to 1997) is similar to the rate of glacial retreat (2.9 m yr-1). In the interval from 1997 to 2002, pioneer species advanced at a rapid rate of 6.4 -12.2 m yr-1 when the glacier retreated at 9.8 m yr-1. Rapid glacial retreat has been accompanied by rapid colonization by plants. Pioneer species improve soil conditions and make habitat suitable for other plants. If warming continues, alpine plant cover may extend all the way to mountain summits, and then eventually diminish as trees colonize the areas formerly occupied by the alpine plants. Larger woody plants such as Senecio keniodendron and Lobelia telekii, which showed no obvious advances before 1997, have advanced quickly since 1997.

Key Words: Vegetation; Deglaciation, Global warming; Environmental change; Alpine zone; Africa.

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