Human communities from the Okavango Delta benefit from the services and goods provided by the wetland ecosystem through its riparian vegetation. These include food and timber products used for the construction of shel...Human communities from the Okavango Delta benefit from the services and goods provided by the wetland ecosystem through its riparian vegetation. These include food and timber products used for the construction of shelter and canoes. Despite the importance of riparian tree species in the Delta, their regeneration structure is currently unknown. For riparian trees to be managed sustainably, information on the current regeneration status of the trees under different land uses is needed. The Moremi game reserve (protected area) and Seronga (communal area) were selected for this study on the regeneration of riparian tree species of Croton megalobotrys Müll. Arg, Philenoptera violacea (Klotzsch) Schrire, Senegalia nigrescens (Acacia nigrescens) Oliv and Diospyros mespiliformis Hochst. ex A. Dc. The height of each individual tree was estimated in randomly selected 30 plots (15 from each site) of 20 × 50 m for assignment to five regeneration classes: 0-0.5, 0.5-1, 1-2, 2-4 and >4 m. Linear regression was used to infer regeneration status of each species. An independent-sample Student’s t test was used to determine any significance differences in seedling density/ha and sapling density/ha between different sites at p < 0.05. Diospyros mespiliformis populations had an unstable regeneration structure in both sites, while P. violacea regeneration was stable regardless of land-use type. Croton megalobotrys and S. nigrescens had an unstable regeneration pattern in Seronga, while in Moremi it was stable; thus, the regeneration structure of C. megalobotrys and S. nigrescens is affected by land-use. This result implies that intervention is needed to conserve the two species in Seronga where the current land-use appears to be incompatible with regeneration; D. mespiliformis also needs to be conserved in both Moremi and Seronga.展开更多
The goals of Integrated Water Resources Management (IWRM) can be achieved by embracing the principles of distributive governance, which places both customary and statutory water institutions on the same pedestal in th...The goals of Integrated Water Resources Management (IWRM) can be achieved by embracing the principles of distributive governance, which places both customary and statutory water institutions on the same pedestal in the governance of water resources. As culture and traditions constitute intangible aspects of water resources management in rural Africa, the recognition of water governance systems grounded in local norms, which correspond better with the aspirations of local water users as against the expert-knowledge systems is desirable. Following the introduction of the statutory institutions in postcolonial Africa, customary institutions, which were once effective in regulating water resources became relegated to the background in those countries, including Botswana . Adopting a critical literature review approach, this article employs the concept of legal pluralism to analyze the institutional factors that create the disharmony between cultural and statutory water governance and management institutions. Findings indicate that water has been abstracted from its social nature and transformed into a tradable economic good. Ultimately, the local meanings and images encoded in water as a nature-given resource are overlooked, thus generating conflicts in water governance. The paper recommends the adoptions of legal pluralism under which water institutions need to embrace both customary and statutory institutions.展开更多
Eulophia angolensis is an endangered plant species found in the Okavango Delta. Generally, there is lack of botanical information on this species in Botswana, which is necessary for its in-situ and ex-situ conservatio...Eulophia angolensis is an endangered plant species found in the Okavango Delta. Generally, there is lack of botanical information on this species in Botswana, which is necessary for its in-situ and ex-situ conservation. The objectives of this research are to map areas where E. angolensis occurs, determine the species that co-exist with it, and establish soil factors that influence its abundance and distribution in the Okavango Delta. A survey of the area where the plant was sighted in 2004 was carried out using recorded GPS points. Soil samples were collected at 0 - 20 cm depth from the floodplain where the species occurred to determine the macronutrients: total nitrogen, phosphorus, potassium (N, P, and K) and soil organic carbon (SOC) contents. The researchers could not find the plant at all GPS locations where the plant was sighted in 2004, but discovered a new unrecorded site for the species. The species was very close to the water channel;approximately 40 cm away, with only one plant about 60 cm away. The mean macronutrients concentrations in the site that contained E. angolensis were total N = 2.61 ± 0.61 mg/L, P = 7.02 ± 0.8 mg/L and K = 14.41 ± 4.28 mg/L. SOC concentration was 40.1 ± 10.28 mg/L. Furthermore, there was K biogeochemical gradient within the E. angolensis habitat, with more concentrations directly around the plant. Therefore, E. angolensis needs critical amounts of N, P, K and SOC, with K, SOC and water requirement being the crucial factors. Frequent monitoring of the endangered species found in the Okavango Delta is required, and ex-situ conservation of the species in the country in the form of a botanical garden should be established for future generations.展开更多
FEW images invoke the feeling of Africa＇s natural beauty more than the Okavango Delta.Yet this environmentally sensitive and economically significant area of Botswana is under threat due to climate change. The Okava...FEW images invoke the feeling of Africa＇s natural beauty more than the Okavango Delta.Yet this environmentally sensitive and economically significant area of Botswana is under threat due to climate change. The Okavango Delta is the world＇s largest inland delta, a permanent swamp that covers over 15,000 square km. The Delta floods yearly, between January and February, but the water, originating in the Angola highlands, evaporates and never reaches the major body of water.展开更多
Introduction:Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning.This understanding can furthe...Introduction:Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning.This understanding can further serve to inform policy aimed at conserving wetlands such as the Okavango Delta.In the Okavango Delta,information on the influence of distance from surface water on vegetation community composition and structure is limited.The objective of this study was to determine the relationship between distance from surface water and riparian plant communities at different sites in the Okavango Delta.Methods:Vegetation sampling was conducted in four sites in 20 m×10 m belted plots placed perpendicular to the river bank at 0–10 m,10–20 m,20–30 m,30–40 m,and 40–50 m distance classes.At each site,10–15 plots were sampled at each distance class.Basal area,species richness,cover,and plant diversity were determined for each plot.Indicator species analysis was used to determine the characteristic species at each distance class.One-way analysis of variance and Tukey post hoc analyses were used to compare species diversity,richness,cover,and basal area between distance classes.Generalized linear mixed(GLM)model was used to test for the overall impact of site and distance on each plant parameter.Results:Mean species richness was significantly(p<0.05)higher at 0–10 m than at 20–30 m,30–40 m,and 40–50 m in Boro.There was no significant difference within other sites.Mean species diversity also varied significantly(p<0.05)in Boro where it was higher at 0–10 m and 10–20 m than at 30–40 m.Mean basal area differed significantly within Jao and Upper Panhandle.In Jao,it was higher(p<0.05)at 0–10 m than at other distance classes.Mean percentage canopy cover differed significantly within all sites.In addition to this,plant species composition also changed along distance from surface water within each site.From GLM analysis,both distance and site significantly(p<0.05)influenced diversity and basal area.Species richness and cover were significantly(p<0.05)influenced by site only.Conclusion:Distance from surface water and site are important determinants of riparian plant dynamics in the Okavango Delta.展开更多
The history of Botswana’s major seismic events has been initiated by two earthquakes that occurred on the 11th of September and 11th of October 1952 with ML Richter magnitudes of 6.1 and 6.7, respectively, in the Oka...The history of Botswana’s major seismic events has been initiated by two earthquakes that occurred on the 11th of September and 11th of October 1952 with ML Richter magnitudes of 6.1 and 6.7, respectively, in the Okavango Delta Region (ODR). Not much is known and well documented about the seismicity of a larger coverage of Botswana primarily because over the years, local seismic stations were biased to the north-western part of Botswana, to monitor the more seismogenic ODR. The objective of this study is to use data from the International Seismological Centre (ISC) bulletin for the period 1966-2012 to estimate the relative size distribution of seismic events (b-value), the rate of seismic activity (a-value), and associated stress condition prevailing in Botswana to assist in the quest of hazard mitigation. This study shows that micro-seismic activities of magnitude ranging from 1.3 to 5.7 are distributed not only on the northern part of Botswana, but also in other parts of the country such as the Southern (including Kweneng East and West), Central and Eastern Botswana. Based on 327 events extracted from data compiled by the ISC, the frequency-magnitude distribution (FMD) of earthquakes in Botswana from 1966 to 2012 was estimated with b-value and a-value for the entire catalogue found to be 1.2 and 6.3, respectively, implying a region of low stress dominated by small to moderate events. The minimum completeness magnitude (MC), a value that indicates the lowest magnitude above which all seismic events are reliably recorded was found to be 3.8. From this analysis, annual probabilities of occurrence for M4 and M5 events were found to be 67.2% and 4.3%, respectively, while M6 or larger event has an annual probability of 0.3%.展开更多
Mechanisms that drive species co-occurrence are poorly documented for intermittent rivers of semiarid regions. Here, we investigated fish community assembly in response to habitat types and physicochemical conditions ...Mechanisms that drive species co-occurrence are poorly documented for intermittent rivers of semiarid regions. Here, we investigated fish community assembly in response to habitat types and physicochemical conditions in intermittent rivers of the lower Okavango Delta, Botswana. Using Joint Species Distribution Models, we inferred relative influences of environmental filtering and species interactions on patterns of species co-occurrence. Fishes were surveyed from multiple locations during drought and flood phases of the annual hydrological cycle. Species were classified into trophic guilds to facilitate inference about the types of species interactions that influence community structure. Water physicochemistry (depth, temperature, and dissolved oxygen concentration) was significantly associated with species distributions, whereas habitat type (ephemeral vs. permanent) was not significantly associated with species distribution. Controlling for the influence of environmental covariates resulted in three negative residual correlations, of which two involved non-predatory fishes from different trophic guilds, suggesting a behavioral selection of, or enhanced survival within, habitats with different environmental conditions. There was a negative residual correlation between a predator and a potential prey species, suggesting a role for predation mortality or threat in species segregation. Our results demonstrate that using trophic guilds in conjunction with JSDMs can enhance inferences about mechanisms of community assembly.展开更多
基金supported by German Federal Ministry for Education and Research
文摘Human communities from the Okavango Delta benefit from the services and goods provided by the wetland ecosystem through its riparian vegetation. These include food and timber products used for the construction of shelter and canoes. Despite the importance of riparian tree species in the Delta, their regeneration structure is currently unknown. For riparian trees to be managed sustainably, information on the current regeneration status of the trees under different land uses is needed. The Moremi game reserve (protected area) and Seronga (communal area) were selected for this study on the regeneration of riparian tree species of Croton megalobotrys Müll. Arg, Philenoptera violacea (Klotzsch) Schrire, Senegalia nigrescens (Acacia nigrescens) Oliv and Diospyros mespiliformis Hochst. ex A. Dc. The height of each individual tree was estimated in randomly selected 30 plots (15 from each site) of 20 × 50 m for assignment to five regeneration classes: 0-0.5, 0.5-1, 1-2, 2-4 and >4 m. Linear regression was used to infer regeneration status of each species. An independent-sample Student’s t test was used to determine any significance differences in seedling density/ha and sapling density/ha between different sites at p < 0.05. Diospyros mespiliformis populations had an unstable regeneration structure in both sites, while P. violacea regeneration was stable regardless of land-use type. Croton megalobotrys and S. nigrescens had an unstable regeneration pattern in Seronga, while in Moremi it was stable; thus, the regeneration structure of C. megalobotrys and S. nigrescens is affected by land-use. This result implies that intervention is needed to conserve the two species in Seronga where the current land-use appears to be incompatible with regeneration; D. mespiliformis also needs to be conserved in both Moremi and Seronga.
文摘The goals of Integrated Water Resources Management (IWRM) can be achieved by embracing the principles of distributive governance, which places both customary and statutory water institutions on the same pedestal in the governance of water resources. As culture and traditions constitute intangible aspects of water resources management in rural Africa, the recognition of water governance systems grounded in local norms, which correspond better with the aspirations of local water users as against the expert-knowledge systems is desirable. Following the introduction of the statutory institutions in postcolonial Africa, customary institutions, which were once effective in regulating water resources became relegated to the background in those countries, including Botswana . Adopting a critical literature review approach, this article employs the concept of legal pluralism to analyze the institutional factors that create the disharmony between cultural and statutory water governance and management institutions. Findings indicate that water has been abstracted from its social nature and transformed into a tradable economic good. Ultimately, the local meanings and images encoded in water as a nature-given resource are overlooked, thus generating conflicts in water governance. The paper recommends the adoptions of legal pluralism under which water institutions need to embrace both customary and statutory institutions.
文摘Eulophia angolensis is an endangered plant species found in the Okavango Delta. Generally, there is lack of botanical information on this species in Botswana, which is necessary for its in-situ and ex-situ conservation. The objectives of this research are to map areas where E. angolensis occurs, determine the species that co-exist with it, and establish soil factors that influence its abundance and distribution in the Okavango Delta. A survey of the area where the plant was sighted in 2004 was carried out using recorded GPS points. Soil samples were collected at 0 - 20 cm depth from the floodplain where the species occurred to determine the macronutrients: total nitrogen, phosphorus, potassium (N, P, and K) and soil organic carbon (SOC) contents. The researchers could not find the plant at all GPS locations where the plant was sighted in 2004, but discovered a new unrecorded site for the species. The species was very close to the water channel;approximately 40 cm away, with only one plant about 60 cm away. The mean macronutrients concentrations in the site that contained E. angolensis were total N = 2.61 ± 0.61 mg/L, P = 7.02 ± 0.8 mg/L and K = 14.41 ± 4.28 mg/L. SOC concentration was 40.1 ± 10.28 mg/L. Furthermore, there was K biogeochemical gradient within the E. angolensis habitat, with more concentrations directly around the plant. Therefore, E. angolensis needs critical amounts of N, P, K and SOC, with K, SOC and water requirement being the crucial factors. Frequent monitoring of the endangered species found in the Okavango Delta is required, and ex-situ conservation of the species in the country in the form of a botanical garden should be established for future generations.
文摘FEW images invoke the feeling of Africa＇s natural beauty more than the Okavango Delta.Yet this environmentally sensitive and economically significant area of Botswana is under threat due to climate change. The Okavango Delta is the world＇s largest inland delta, a permanent swamp that covers over 15,000 square km. The Delta floods yearly, between January and February, but the water, originating in the Angola highlands, evaporates and never reaches the major body of water.
基金This study which is part of GT’s PhD work was sponsored by the German Federal Ministry for Education and Research(BMBF).
文摘Introduction:Understanding the environmental factors that influence riparian vegetation community composition and distribution is important for understanding wetland ecosystem functioning.This understanding can further serve to inform policy aimed at conserving wetlands such as the Okavango Delta.In the Okavango Delta,information on the influence of distance from surface water on vegetation community composition and structure is limited.The objective of this study was to determine the relationship between distance from surface water and riparian plant communities at different sites in the Okavango Delta.Methods:Vegetation sampling was conducted in four sites in 20 m×10 m belted plots placed perpendicular to the river bank at 0–10 m,10–20 m,20–30 m,30–40 m,and 40–50 m distance classes.At each site,10–15 plots were sampled at each distance class.Basal area,species richness,cover,and plant diversity were determined for each plot.Indicator species analysis was used to determine the characteristic species at each distance class.One-way analysis of variance and Tukey post hoc analyses were used to compare species diversity,richness,cover,and basal area between distance classes.Generalized linear mixed(GLM)model was used to test for the overall impact of site and distance on each plant parameter.Results:Mean species richness was significantly(p<0.05)higher at 0–10 m than at 20–30 m,30–40 m,and 40–50 m in Boro.There was no significant difference within other sites.Mean species diversity also varied significantly(p<0.05)in Boro where it was higher at 0–10 m and 10–20 m than at 30–40 m.Mean basal area differed significantly within Jao and Upper Panhandle.In Jao,it was higher(p<0.05)at 0–10 m than at other distance classes.Mean percentage canopy cover differed significantly within all sites.In addition to this,plant species composition also changed along distance from surface water within each site.From GLM analysis,both distance and site significantly(p<0.05)influenced diversity and basal area.Species richness and cover were significantly(p<0.05)influenced by site only.Conclusion:Distance from surface water and site are important determinants of riparian plant dynamics in the Okavango Delta.
文摘The history of Botswana’s major seismic events has been initiated by two earthquakes that occurred on the 11th of September and 11th of October 1952 with ML Richter magnitudes of 6.1 and 6.7, respectively, in the Okavango Delta Region (ODR). Not much is known and well documented about the seismicity of a larger coverage of Botswana primarily because over the years, local seismic stations were biased to the north-western part of Botswana, to monitor the more seismogenic ODR. The objective of this study is to use data from the International Seismological Centre (ISC) bulletin for the period 1966-2012 to estimate the relative size distribution of seismic events (b-value), the rate of seismic activity (a-value), and associated stress condition prevailing in Botswana to assist in the quest of hazard mitigation. This study shows that micro-seismic activities of magnitude ranging from 1.3 to 5.7 are distributed not only on the northern part of Botswana, but also in other parts of the country such as the Southern (including Kweneng East and West), Central and Eastern Botswana. Based on 327 events extracted from data compiled by the ISC, the frequency-magnitude distribution (FMD) of earthquakes in Botswana from 1966 to 2012 was estimated with b-value and a-value for the entire catalogue found to be 1.2 and 6.3, respectively, implying a region of low stress dominated by small to moderate events. The minimum completeness magnitude (MC), a value that indicates the lowest magnitude above which all seismic events are reliably recorded was found to be 3.8. From this analysis, annual probabilities of occurrence for M4 and M5 events were found to be 67.2% and 4.3%, respectively, while M6 or larger event has an annual probability of 0.3%.
文摘Mechanisms that drive species co-occurrence are poorly documented for intermittent rivers of semiarid regions. Here, we investigated fish community assembly in response to habitat types and physicochemical conditions in intermittent rivers of the lower Okavango Delta, Botswana. Using Joint Species Distribution Models, we inferred relative influences of environmental filtering and species interactions on patterns of species co-occurrence. Fishes were surveyed from multiple locations during drought and flood phases of the annual hydrological cycle. Species were classified into trophic guilds to facilitate inference about the types of species interactions that influence community structure. Water physicochemistry (depth, temperature, and dissolved oxygen concentration) was significantly associated with species distributions, whereas habitat type (ephemeral vs. permanent) was not significantly associated with species distribution. Controlling for the influence of environmental covariates resulted in three negative residual correlations, of which two involved non-predatory fishes from different trophic guilds, suggesting a behavioral selection of, or enhanced survival within, habitats with different environmental conditions. There was a negative residual correlation between a predator and a potential prey species, suggesting a role for predation mortality or threat in species segregation. Our results demonstrate that using trophic guilds in conjunction with JSDMs can enhance inferences about mechanisms of community assembly.
