Blackthorn Research Articles

Woody vegetation change over more than 30 years in the interior duneveld of the Kalahari Gemsbok National Park

Background and objectives: Long-term studies of woody plants in South Africa are scarce. This study, initiated in the late 1970s, therefore aids understanding of vegetation dynamics in the southern Kalahari by investigating woody vegetation change at and away from a watering point. Methods: At three sites, all woody individuals were counted by species in plots 0.5 or 1 ha in size. Seedlings were noted separately from the >0.2 m group of individuals. Results: Vachellia erioloba and shrub density decreased over time whereas dwarf shrub species’ numbers fluctuated markedly. Additionally, no increase in density of known bush encroaching species (e.g. Grewia flava, Rhigozum trichotomum and Senegalia mellifera) was found in this large conservation area. Discussion and conclusion: The changes in density of the woody species seem to point to the importance of particular rainfall patterns or sequences of events over different years that are responsible for these changes in the southern Kalahari, and the evident lack of bush encroachment in this conservation area supports the notion that bush encroachment in arid savannas is driven primarily by land-use practices and not by elevated carbon dioxide levels that are sometimes provided as cause for encroachment.

Growth ring formation of Dichrostachys cinerea and Senegalia mellifera in arid environments in Namibia

Dichrostachys cinerea and Senegalia mellifera trees are the most widespread invasive encroacher species in Namibia. Understanding their growth performance under arid conditions is key to understanding and managing the arid ecosystems of Namibia. To determine their utility in dendrochronology, we analyzed the formation of growth rings for two species from three sites in Namibia. We applied cross-dating techniques to 69 tree discs, the analysis of which confirmed the formation of annual growth rings. The rings are characterised by alternating layers of low and high vessel density and are separated by bands of marginal parenchyma. D. cinerea shows a well-defined pattern of growth rings, whereas the ring patterns of S. mellifera are more complex. Because aging trees tend to display narrower rings toward the outside of the stem, we applied both ring-width index and basal area increment methods in developing ring-width chronologies for the two species. Descriptive statistics for the chronologies indicate that the average ring chronologies are of good quality and that the trees are responding to common environmental signals. The basal area increment methodology produced better statistics than the ring-width index for these two species. Furthermore, statistical characteristics of the chronologies indicate that D. cinerea has a higher mean sensitivity (MS), expressed population signal (EPS), and signal-to-noise ratio (SNR) than S. mellifera. Thus, we find that both species are suitable for dendrochronological study, with D. cinerea being better than S. mellifera.

Partitioning of Water Between Differently Sized Shrubs and Potential Groundwater Recharge in a Semiarid Savanna in Namibia.

Introduction: Many semiarid regions around the world are presently experiencing significant changes in both climatic conditions and vegetation. This includes a disturbed coexistence between grasses and bushes also known as bush encroachment, and altered precipitation patterns with larger rain events. Fewer, more intense precipitation events might promote groundwater recharge, but depending on the structure of the vegetation also encourage further woody encroachment. Materials and Methods: In this study, we investigated how patterns and sources of water uptake of Acacia mellifera (blackthorn), an important encroaching woody plant in southern African savannas, are associated with the intensity of rain events and the size of individual shrubs. The study was conducted at a commercial cattle farm in the semiarid Kalahari in Namibia (MAP 250 mm/a). We used soil moisture dynamics in different depths and natural stable isotopes as markers of water sources. Xylem water of fifteen differently sized individuals during eight rain events was extracted using a Scholander pressure bomb. Results and Discussion: Results suggest the main rooting activity zone of A. mellifera in 50 and 75 cm soil depth but a reasonable water uptake from 10 and 25 cm. Any apparent uptake pattern seems to be driven by water availability, not time in the season. Bushes prefer the deeper soil layers after heavier rain events, indicating some evidence for the classical Walter’s two-layer hypothesis. However, rain events up to a threshold of 6 mm/day cause shallower depths of use and suggest several phases of intense competition with perennial grasses. The temporal uptake pattern does not depend on shrub size, suggesting a fast upwards water flow inside. δ2H and δ18O values in xylem water indicate that larger shrubs rely less on upper and very deep soil water than smaller shrubs. It supports the hypothesis that in environments where soil moisture is highly variable in the upper soil layers, the early investment in a deep tap-root to exploit deeper, more reliable water sources could reduce the probability of mortality during the establishment phase. Nevertheless, independent of size and time in the season, bushes do not compete with potential groundwater recharge. In a savanna encroached by A. mellifera, groundwater will most likely be affected indirectly.

Classification, description and mapping of the vegetation in Khutse Game Reserve, Botswana

There is currently no detailed classification and description of plant communities in Khutse Game Reserve (KGR), Botswana, using phytosociological techniques. The main aim of this study was to classify and describe plant communities in KGR. Classification and description of plant communities will help in understanding the plant ecology of KGR. Braun-Blanquet sampling method was applied in 91 stratified random relevés. Nine plant communities were identified and classified using Modified TWINSPAN which is contained in JUICE program. The results showed that there was a statistically significant difference in percentage cover of herbaceous plants between the different plant communities. Schmidtia pappophoroides-Stipagrostis uniplumis and Heliotropium lineare-Enneapogon desvauxii communities had higher cover (%) of herbaceous plants than other communities. Catophractes alexandri-Stipagrostis uniplumis community had the highest cover (%) of shrubs. There was no statistically significant difference in plant species diversity (Shannon-Wienner Index) and species evenness between plant communities, but there was a statistically significant difference in plant species richness between the different plant communities. Dichrostachys cinerea-Grewia flava community, Senegalia mellifera subsp. detinens-Maytenus species community and Catophractes alexandri-Stipagrostis uniplumis community had lower number of species, whereas Vachellia luederitzii var. retinens-Grewia flava community had the highest number (46) of plant species. This study will help the Department of Wildlife and National Parks (DWNP) to develop an updated and informed Management Plan for the reserve, which takes cognizance of the plant ecology of the reserve.

Effects of substrate on germination and growth of Moringa oleifera Lam., Acacia mellifera (Vahl) Benth. and Zizyphus mauritiana Lam. seedlings

Despite the importance of forests and trees, Senegal is facing to the loss of forests and the decline of tree diversity and density. This study focuses on Moringa oleifera Lam., Acacia mellifera (Vahl) Benth. and Zizyphus mauritiana Lam. which constitute a significant source of food and economic value for the populations of Casamance.In addition to a germination test, a follow-up of seedlings on different substrates was carried out in the nursery, in order to determine the effect of substrates on some growth parameters (number of leaves, height, diameter and biomass).The substrates used were three potting mixtures of forest soil of Faidherbia albida (FSFA), Elaeis guineensis (FSEG) and Anacardium occidentale (FSAO) and sand with the following proportion: 1/3 sand + 2/3 forest soil). Based on species, the germination rate was higher for A. mellifera (84%) followed by M.oleifera (55%) and Z. mauritiana (50%). The germination rate was more important in FSFA and FSEG than in FSAO. For growth parameters, there was a significant effect (P<0.05) of substrate type on height, diameter, number of leaves and root biomass. In term of growth parameters, the seedling performed better in FSFA and FSEG than in FSAO. The species effect was also significant (P<0.05) with higher root biomass and diameter found in M. oleifera and height and number of leaves in A. mellifera. The most important total biomass was found in FSFA followed by FSEG. Comparing the fraction of biomass according to the part of the seedling, the stem and branch had the higher fraction of biomass for A. mellifera (43%) and M. oleifera (38%) and the leaves for Z. mauritiana (46%).However, thetype of substrate can affect seedling development and growth parameters and the better results were recorded in FSFA and FSEG substrates.

The Use of Seed Vigour Tests for Predicting Field Emergence

The general aim of this study was to address the problem of seed vigour testing in Acacia senegal and Acacia mellifera) by studying different seed vigour tests and comparing them to identify the most suitable test for each species. The importance of this study lies in the fact that vigour testing measures the percentage of viable seeds in a sample as well as their ability to produce normal seedlings under less than optimum or adverse growing conditions, similar to those occurring in the field. To achieve this objective, a set of laboratory and field tests were conducted for the two Acacia species. Data collected included: The number of seeds per kilogram, germination percentage, seedling shoot length, seedling root length, seedling root wet and dry weight, seedling shoot wet and dry weight. The cutting test, electrical conductivity tetrazolium test and Hiltner test were employed to determine the seed vigour.
 The results showed that Acacia mellifera had a high electrical conductivity, indicating its low seed vigour. The electrical conductivity of Acacia senegal was equivalent to that of distilled water, indicating that either the seed coat was intact or no ions were leached from the seeds. Comparison of the various tests suggests that Hiltner test is the most accurate” or “reliable”) test for seed vigor.

Trends of phanerophyte encroacher species along an aridity gradient on Kalahari sands, central Namibia

Abstract Poor rangeland management, especially overstocking and under-burning coupled with climate change on southern African savannas, have brought about a serious ecological problem of bush encroachment. Bush encroachment leads to many ecological implications such as extirpation or extinction of plant species and a colonisation by opportunistic species leading to unwanted changes in plant species composition, structure and loss of species diversity. Furthermore, bush encroachment has a negative impact on the country’s progress in terms of conservation efforts, economic stability and livelihood. Namibian livestock ranchers forego an estimated N$ 700 million loss yearly linked to bush encroachment. Studies focusing on particular bush encroacher species enable the devise of ecologically sound management strategies by land manager, farmers and scientists for the prevention and control of bush encroachment. Therefore, this study was undertaken to determine the main encroacher species and their relationship to the environmental factors along an aridity gradient on Kalahari sands in central Namibia. Results disclosed that Acacia erioloba E.Mey., Acacia mellifera (Vahl) Benth. ssp. dentines (Burch.) Brenan, Combretum collinum Fresen., Terminalia sericea Burch. Ex DC., Grewia spp., Bauhinia petersiana Bolle ssp. macrantha (Oliv.) Brummitt & J.H. Ross were the main encroacher species, and mean annual rainfall was the main environmental factor influencing their distribution. Nanophanerophyte from different encroacher species were recorded mainly from 400 mm to 500 mm mean annual rainfall, mesophanerophyte recorded from 280 mm to 450 mm, while microphanerophyte were widely distributed over the rainfall gradient. Bush encroachment was recorded at 440 mm mainly due to the poor rangeland management. Information from this study should be used as a baseline for conservation and restoration attempts towards savanna rangelands.

English

Understanding the socioeconomic and environmental impacts of invasive plant species from the affected communities’ perspectives is essential to design and plan sustainable control and prevention strategies. Hence, understanding the socio-economic and environmental impacts in the infested and susceptible areas such as Bale zone is very crucial. Therefore, the objective of this study was to assess socio-economic impacts of in lowlands of Bale zone, Southeastern Ethiopia. House hold survey, focus group discussion and key informant interview to understand socio-economic and environmental impacts invasive plant species were used. Statistical package for social sciences (SPSS) (v. 20) was used for data collection. The results showed that a total of 12 invasive plant species were recorded, and of which Parthenium hysterophorus, Xanthium strumarium, Argemone ochroleuca, Ceasalpinia spp, Acacia bussie, Acacia mellifera, Acacia seyal and Acacia tortolis were highly distributed in the study areas. Respondents reported that heavy infestation of invasive plant species were found on the roadsides followed by arable land. The invasive plant species has also certain economic and ecological benefits. The local communities blame the invasive plant species for their negative impacts on biodiversity, degrading ecosystems, livestock and livestock products, crops, animal and human health. The study result showed that the local community utilizes chemical, mechanical and biological methods to reduce and control the impacts even though the percent of households that were trying to control is very low. Community perception showed the invasive plants species infesting grazing lands, crop lands, road sides, frosts and settlement areas. However, much has not been done to alert the local people on the danger of environmental impacts on biodiversity, agriculture and health. The menace of the species is increasing at an alarming rate, thus control methods have to be designed to stop further spreading into Bale Mountain National Parks. Key words: Environmental impacts, invasive alien species, socio-economic impacts, Southeast Ethiopia.

Impacts of a mineral lick-centred land use system on woody vegetation cover in an East African Savannah

Evaluation of woody vegetation changes with distance from a salt crater was conducted in the semi‐arid rangelands of southern Ethiopia. Data on live woody plants were collected over three seasons at 0, 1, 4, 6, 9 and 12 km from the salt crater. The density and diversity of woody plants differed significantly (p < .01) along the distance gradient. Six woody plant families were identified of which Fabaceae and Burseraceae were the dominant families. Acacia drepanolobium, Acacia nilotica, Commiphora africana and Acacia mellifera were among the severely encroaching woody species. There were high proportions of seedlings and saplings recorded closer to the salt crater showing a vigorous recruitment by woody plants. Woody plant encroachment along the 12‐km transect ranged from a low to severe encroachment, which could be translated into poor rangeland condition. Changes in soil characteristics increased grazing pressure and sedentary settlement around the salt crater, and the breakdown of traditional institutions seems to be major contributing factors to these vegetation changes. We suggest that severely encroached areas could be improved through a combination of methods such as bush clearing, prescribed fire, browsing animals and proper grazing management.

Incidence and Level of Mistletoe Infestation in Tree Species at Botswana University of Agriculture and Natural Resources' Sebele Content Farm Campus, Botswana

A survey was conducted at Botswana University of Agriculture and natural Resources at Sebele content farm to determine the intensity and level of mistletoe infestation in tree species. The intensity and the total number of trees per tree species infected by the parasitic weed were determined. Acacia eriobola, Acacia mellifera, Terminalia sericea, Ziziphus mucronata, Schinus molle, Acacia tortilis, Acacia erubesens and Acacia flekii hosted the highest number of mistletoe. Results revealed significant variation in level of mistletoe infestation between tree species. A 100% infestation was recorded in some tree species such as Acacia eriobola and Ziziphus mucronata. Severely infested indigenous tree species were dying, whereas most of the exotic tree species were either not infested or have very little number of mistletoe on them. The variation observed could be due to the fact that indigenous species the frequently visited by dispensers looking for food and shelter than exotic species. In addition, there is a possibility that the mistletoe species co-evolved with the indigenous tree species and the vector may be well established on the host tree species than on exotic species.

Antiinflammatory, analgesic and antipyretic effects of dichloromethane stem bark extract of Acacia mellifera

The present study was designed to assess the in vivo antiinflammatory, analgesic and antipyretic effect of the dichloromethane stem bark extract of Acacia mellifera on experimental animal model at three different dose levels of 50, 100 and 150mg/kg body weight respectively. In addition, phytochemical screening of the extract was done. The inflammatory effect was evaluated by use of carragenaan-induced paw edema in mice, pain was determined using formalin-induced writhing in mice and pyrexia was determined by turpentine-induced pyrexia in rats. The activity of the herbal extract was compared to diclofenac sodium and aspirin. The phytochemical analysis showed the presence of alkaloids, cardiac glycosides, flavonoid, saponins, steroids, terpenoids, tannins and phenolics. The plant extract produced marked anti-inflammatory effect in carrageenaninduced mice paw edema assay, suppressed licking response of animals in both phases of the formalin- induced test and exhibited appreciable antipyretic effects in turpentine-induced pyrexia in rats. The study thus supports the folklore use of the plant in the treatment and management of inflammation, pain and pyrexia.

Large shrubs increase soil nutrients in a semi-arid savanna

The soil under savanna woody species is often enriched in nutrients in what is termed an ‘island of fertility’. We tested for positive feedbacks between encroaching woody plants and soil fertility in two co-occurring shrub species at three sites. One of these shrub species is nitrogen-fixing, Acacia mellifera, and the other is non‑nitrogen-fixing, Tarchonanthus camphoratus; we compared these effects to the grasslands surrounding the shrub patches. We found that soil nutrient concentrations were usually related to shrub size rather than the species. Fertile patches developed underneath large shrubs as indicated by higher carbon and nitrogen concentrations, a higher CECeff (especially sodium, which is a limiting nutrient for grazing livestock) and a pH near 6. We found no difference in soil nitrogen between the N-fixing A. mellifera and T. camphoratus. Plant cover under large shrubs was less than in open grassland. There are ‘islands of fertility’ under large shrubs. However, the development of fertility islands did not facilitate understorey growth. Thus, increased soil fertility had no positive feedback on overall vegetation composition. Negative effects of the woody vegetation may override the positive effects of increased soil nutrient availability.

Evaluation of traditionally used medicinal plants for anticancer, antioxidant, anti-inflammatory and anti-viral (HPV-1) activity

The aim of this study was to determine the anticancer, antioxidant, anti-inflammatory and antiviral activities of traditionally used medicinal plants.The extracts were tested for cytotoxicity against human melanoma (A375), epidermoid carcinoma (A431), cervical epithelial carcinoma (HeLa) and human embryonic kidney cells (HEK-293). The antioxidant and anti-inflammatory activities were also determined. Gomphocarpus fruticosus, Helichrysum kraussii and Syzygium jambos were selected for activity against the herpes simplex virus type-1.The extracts exhibited low toxicity towards HEK-293 cells, and four extracts; namely Acacia mellifera, G. fruticosus, H. kraussii and S. jambos, were able to inhibit the A431 and HeLa cells with 50% inhibitory concentrations (IC50) ranging from 34.90–56.20μg/ml. Arbutus unedo, Combretum molle, Dissotis princeps, Erythrophleum lasianthum, Harpephyllum caffrum, H. kraussii and S. jambos, showed high DPPH inhibitory activity, with IC50 values ranging from 2.41–5.25μg/ml. The highest antioxidant activity was seen for S. jambos (DPPH) and A. unedo (NO) respectively with greater activity than ascorbic acid. D. princeps, H. caffrum, Leucas martinicensis and S. jambos, showed high inhibition of the cyclooxygenase-2 (COX-2) enzyme with IC50 values ranging from 3.79–25.80μg/ml with S. jambos showing the highest activity. S. jambos further showed the highest anti-HSV-1 activity at 50.00μg/ml against 100TCID50virus challenge dose.This is the first report of the selected plants for their cytotoxicity, anti-inflammatory and viral inhibitory activity. S. jambos was able to show high inhibition of the HPV type-1 virus and the COX-2 enzyme.

Fuelwood preferences, use and availability in the #Khomani San resettlement farms, southern Kalahari, South Africa

Local level assessments of fuelwood preferences, demand and supply are important for ensuring a balance between ecological functions and livelihood needs. This study reports on an examination of fuelwood preferences, use and abundance in the #Khomani San resettlement farms in southern Kalahari, South Africa. The results show that Acacia erioloba was the most preferred fuelwood species, while Acacia mellifera was abundant but avoided. Across the study area, there were approximately 64 trees ha−1 but riverine sites had significantly more trees (approximately 80 trees ha−1) than non-riverine sites (48 trees ha−1). Live trees showed evidence of damage (cutting or breaking) and this was more pronounced in the riverine sites (close to human settlement) than in the non-riverine sites. However, overall current woody stocks and productivity rates of harvestable fuelwood are well above current fuelwood demand, suggesting fuelwood use may be within sustainable limits, though there is evidence of localised fuelwood depletion. The implications of these results for fuelwood management interventions, including the importance of context, are discussed.

Indigenous and Medicinal Uses of Plants in Nech Sar National Park, Ethiopia

For many years humans have used different parts of plants for medicinal purposes, as source of food and feed. Hence the benefits of indigenous knowledge for the development of present day sophisticated medicinal inventions cannot be overlooked. Indigenous people living in and around protected areas are still making use of plants to cure human and animal related diseases. Guji, Kore and Gamo people of Nech Sar National Park are not indifferent to this fact. Primary data were collected from these indigenous communities of the area and concerned government officers by making use of interview questions and observation. In addition to this, information was also gathered from the operational and management staff of Nech Sar National Park through semi-structured questionnaire. Then data were transcribed and analyzed by making use of descriptive statistics and content analysis. The findings of the study showed, from the vegetation of Nech Sar National Park, a total of 12 plants are being used as a medicinal remedy for humans and livestock health related problems. Croton macrostachys (for skin infection), Balanites aegyptiaca (constipation and other intestinal problems), Aleo vera (joint pains and as a deworming), Acacia mellifera (treating ringworm) and Solanum incanum (treat livestock infected with water born parasites) are among the major plants which are being used as a local remedy to treat health complications by the indigenous community. Apart from this, the different parts of these plants are also used for processing food items in the household. The research found out that the local communities have strong faith on these plants as they have been used across generations so as to combat various diseases in an indigenous way. Therefore, policy and strategic actions should consider the preservation of indigenous knowledge along with biodiversity resources as indigenous technical knowledge will continue to shape up the development efforts of the present generation.

Characterization and functional properties of some natural Acacia gums

Authentic representative gum exudate samples from Acacia species namely Acacia senegal var. senegal (ASG), Acacia mellifera (AMF), Acacia seyal var. seyal (ASY), and Acacia tortilis var. raddiana (ATR), were physicochemically analyzed. The moisture, ash, nitrogen and protein content, pH, specific optical rotation, and number average molecular weight were found to be ranging from 9.76% to 8.35%, 3.40% to 2.05%, 0.243% to 1.549%, 1.610% to 10.378%, 4.45 to 4.94, −48.25 to +86.75 and 0.24×106 to 2.95×106 respectively. The 13C and 1H NMR spectra of gum samples showed similarity in individual sugar components, but characteristic patterns of each gum, were observed. FTIR spectra of the studied gums show the presence of the same functional groups in the four gums. DSC and TGA thermograms were characteristic for each gum. Evaluation of the functional properties of the four gums indicated that ATR gum bears the best emulsification characteristics in terms of emulsion’s stability and emulsification power.

Examining the Spectral Separability of Prosopis glandulosa from Co-Existent Species Using Field Spectral Measurement and Guided Regularized Random Forest

The invasive taxa of Prosopis is rated the world’s top 100 unwanted species, and a lack of spatial data about the invasion dynamics has made the current control and monitoring methods unsuccessful. This study thus tests the use of in situ spectroscopy data with a newly-developed algorithm, guided regularized random forest (GRRF), to spectrally discriminate Prosopis from coexistent acacia species (Acacia karroo, Acacia mellifera and Ziziphus mucronata) in the arid environment of South Africa. Results show that GRRF was able to reduce the high dimensionality of the spectroscopy data and select key wavelengths (n = 11) for discriminating amongst the species. These wavelengths are located at 356.3 nm, 468.5 nm, 531.1 nm, 665.2 nm, 1262.3 nm, 1354.1 nm, 1361.7 nm, 1376.9 nm, 1407.1 nm, 1410.9 nm and 1414.6 nm. The use of these selected wavelengths increases the overall classification accuracy from 79.19% and a Kappa value of 0.7201 when using all wavelengths to 88.59% and a Kappa of 0.8524 when the selected wavelengths were used. Based on our relatively high accuracies and ease of use, it is worth considering the GRRF method for reducing the high dimensionality of spectroscopy data. However, this assertion should receive considerable additional testing and comparison before it is accepted as a substitute for reliable high dimensionality reduction.

Land use, rangeland degradation and ecological changes in the southern Kalahari, Botswana

AbstractDual‐scale analyses assessing farm‐scale patterns of ecological change and landscape‐scale patterns of change in vegetation cover and animal distribution are presented from ecological transect studies away from waterpoints, regional remotely sensed analysis of vegetation cover and animal numbers across the southern Kalahari, Botswana. Bush encroachment is prevalent in semi‐arid sites where Acacia mellifera Benth. is widespread in communal areas and private ranches, showing that land tenure changes over the last 40 years have not avoided rangeland degradation. Herbaceous cover is dominated in intensively grazed areas by the annual grass Schmidtia kalahariensis Stent and in moderately grazed areas by the perennial grass Eragrostis lehmanniana Nees. Nutritious perennial grass species including Eragrostis pallens Hack. Ex Schinz remain prevalent in Wildlife Management Areas. Other ecological changes include the invasion of the exotic Prosopis glandulosa Torr. and dense stands of Rhigozum trichotomum Kuntze. in the arid southwest. Regional patterns of wildlife species show that the expansion of cattleposts and fenced ranches has led to large areas of low wildlife conservation value even in areas where cattle production is not practiced. Findings show the need for integrated landscape‐scale planning of land use if the ecological value and biodiversity of the southern Kalahari is to be retained.

Changes in landscape vegetation, forage plant composition and herding structure in the pastoralist livelihoods of East Pokot, Kenya

ABSTRACTOral evidence from pastoral Pokot on vegetation changes in the rangelands of northern Baringo District points to major changes in structure and biodiversity composition over the past century. A landscape of perennial grasses has turned into an Acacia-dominated bush-land. Pelil (Acacia nubica), talamogh (Acacia mellifera), or anyua (Acacia reficiens), which characterise the pastoral landscape today, have increased rapidly since the 1950s. This article compares perceptions of current changes in grass compositions with former accounts, highlighting local assessments of declining high-quality grasses such as abrute (Brachiaria deflexa, Setaria homonyma) or puyun (Eragrostis cilianensis). The changes described are linked to a number of causal factors (high grazing pressure, restriction of pastoral mobility, increasing population numbers), allowing us to historicise the profound change in landscape vegetation. The costs and benefits of bush encroachment are also examined. The tremendous increase in goat numbers, and the sizeable growth of camel herds, is closely connected to the increased availability of fodder plants for browsers. The article concludes by contrasting the views expressed on landscape by Pokot elders with scientific accounts of environmental change.

Evolution of Antimicrobial, Antioxidant Potentials and Phytochemical Studies of Three Solvent Extracts of Five Species from &amp;lt;i&amp;gt;Acacia&amp;lt;/i&amp;gt; Used in Sudanese Ethnomedicine

The ethanol, chloroform and acetone extracts of five species from Acacia (Acacia albidia stems, Acacia mellifera aerial parts, Acacia nubica aerial parts, Acacia seyal var. seyal stems and Acacia tortilis aerial parts) were investigated for their antimicrobial activity against two standard bacterial strains of Gram +ve bacteria (Staphylococcus aureus (ATCC 25923)), Gram -ve bacteria (Pseudomonas aeruginosa (ATCC 27853)) and standard fungi Candida albicans (ATCC 90028) using the agar-plate well diffusion method. The chloroform extract was inactive compared to ethanol and acetone extracts. But ethanol extracts showed the maximum antimicrobial activity against the test organism. Amongst the plant species screened, ethanol extract of Acacia seyal stems showed maximum inhibitory activity (38 mm) and (37 mm) against Staphylococcus aureus and Candida albicans, respectively. The ethanol, chloroform and acetone extracts of Acacia mellifera (aerial parts) did not show any activity against the test organisms. Cholorophorm and acetone extracts via DPPH, the radical scavenging activities were found to be 91 ± 0.03, 88 ± 0.01 and 85 ± 0.04, respectively. The results of phytochemical screening showed that all extracts of studied plant contain flavonoids, saponins, terpenoids, steroids, alkaloids, phenols and tannins.