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The increasing growth of agroindustrial activity resulting in excessive amounts of agriwaste has led to the accumulation of a large quantity of lignocellulosic residues all over the world, in particular in deforestation initiatives for the removal of invasive trees in South Africa. These lignocellulosic residues are rich in energy resources and consist of a mixture of natural polymers based on lignin, cellulose, and hemicellulose. The use of lignolytic fungi such as mushrooms in solid‐state fermentation could sufficiently degrade the indigestible lignocellulosic components and add medicinal and nutritional value to otherwise unusable, high‐energy waste material, which in turn could yield a new method of producing energy‐rich fodder for ruminant animals. The digestive type of animal for which the potential feed is developed must be identified and considered before deciding on the bioconversion method and process, as the outcomes for obtaining potentially high‐quality feeds for nonruminant and ruminant animals are different. The current study presents data on the bioconversion of lignocellulosic substrate using solid‐state fermentation with edible and medicinal mushrooms, Ganoderma lucidumand Pleurotus ostreatus, and a possible new species, to increase digestibility and nutritional value to be applied as ruminant animal feed. The solid‐state fermentation process was optimized and the resulting product was analyzed for the degradation of the lignocellulosic components. Results indicated that the solid‐state fermentation duration and mushroom species were key components in achieving significant degradation. Data obtained after 18 weeks of degradation indicated a significant (p < 0.05) reduction in the acid detergent fiber, acid detergent lignin, and neutral detergent fiber fractions of the biomass, with up to a 20% reduction in indigestible components. This increase in digestibility could contribute to increased energy availability for ruminant animals. [ABSTRACT FROM AUTHOR]

Effects of large mammalian herbivores on woody vegetation tend to be heterogeneous in space and time, but the factors that drive such heterogeneity are poorly understood. We examined the influence of fine‐scale habitat heterogeneity on the distribution and browsing effects of two of the largest African terrestrial mammals, the elephant and giraffe. We conducted this study within a 120‐ha (500 x 2,400 m) ForestGEO long‐term vegetation monitoring plot located at Mpala Research Center, Kenya. The plot traverses three distinct topographic habitats ("plateau," "steep slopes," and "valley") with contrasting elevation, slope, soil properties, and vegetation composition. To quantify browsing damage, we focused on Acacia mellifera, a palatable tree species that occurs across the three habitat categories. Overall tree density, species richness, and diversity were highest on the steep slopes and lowest on the plateau. Acacia mellifera trees were tallest and had the lowest number of stems per tree on the steep slopes. Both elephant and giraffe avoided the steep slopes, and their activity was higher during the wet season than during the dry season. Browsing damage on Acacia mellifera was lowest on the steep slopes. Elephant browsing damage was highest in the valley, whereas giraffe browsing damage was highest on the plateau. Our findings suggest that fine‐scale habitat heterogeneity is an important factor in predicting the distribution of large herbivores and their effects on vegetation and may interact with other drivers such as edaphic variations to influence local variation in vegetation structure and composition. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Honey bees are pollinators that play a key-role in plant biodiversity conservation and crop production. This unique insect species has been managed in hives by beekeepers for millennia, even though such a peculiar animal production system never resulted in the domestication of the western honey bee. The western honey bee was originally distributed throughout most of Europe, Africa, the Middle East, part of the Arabian Peninsula and some parts of Central Asia. From Europe, the honey bee was introduced to America, Asia and Oceania. This adaptation to a range of environmental conditions, together with geological and climatic changes in past eras, has resulted in grouping of Apis mellifera into 31 subspecies. In the last 150 years, technological advances in beekeeping and globalisation have heavily endangered conservation of the native subspecies of A. mellifera in Europe, with an impact on honey bee production and health status. Evaluation of the impact of this phenomenon on the ecological equilibrium is still ongoing, but there is already scientific evidence of negative effects that this problem is having on beekeeping. This document sets forth the scientific arguments in support of the conservation of native subspecies, and lists the existing Italian legislation in terms of subspecies protection initiatives. It also lists the main factors that are contributing to loss of genetic diversity and of local adaptations. This document does not intend to oppose the actions of the beekeeping industry, but rather to contribute to a more global vision of the very serious problem of honey bee decline. [ABSTRACT FROM AUTHOR]

Nosema ceranae causes widespread infection in adult workers of European honey bees, Apis mellifera, and has often been linked to honey bee colony losses worldwide. Previous investigations of honey bee immune response to N. ceranae infection were largely based on laboratory experiment, however, little is known about the immune response of honey bees that are naturally infected by N. ceranae. Here, we compared the infection levels of N. ceranae in three different categories of adult bees (emergent bees, nurses, and foragers) and detected the host immune response to the N. ceranae infection under natural conditions. Our studies showed that the Nosema spore load and infection prevalence varied among the different types of adult workers, and both of them increased as honey bees aged: No infection was detected in emergent bees, nurses had a medium spore load and prevalence, while foragers were with the highest Nosema infection level and prevalence. Quantification of the mRNA levels of antimicrobial peptides ( abaecin, apidaecin, defensin-1, defensin-2, and hymenoptaecin) and microbial recognition proteins ( PGRP-S1, PGRP-S2, PGRP-S3, PGRP-LC, GNBP1-1, and GNBP1-2) confirmed the involvement of the Toll and/or Imd immune pathways in the host response to N. ceranae infection, and revealed an activation of host immune response by N. ceranae infection under natural conditions. Additionally, the levels of immune response were positively correlated with the Nosema spore loads in the infected bees. The information gained from this study will be relevant to the predictive modeling of honey bee disease dynamics for Nosema disease prevention and management. [ABSTRACT FROM AUTHOR]

The chemical control of thickened woody savanna layers is a common practice applied in southern Africa to release the grass layer from competitive pressure and restore the economic viability of rangelands. We comparatively assessed the composition, density and production of the grass layer in relation to the woody vegetation structure following the selective control of increaser woody species (SC) and non-selective control of the whole woody layer (NSC) in a semi-arid Kalahari savanna. Vegetation states associated with bush-thickening preventative range management (PRM) served as a benchmark. The SC treatment created a well-structured woody layer and favored the development of a grassy savanna state with abundant valuable forage grasses, as found under PRM. Despite a high dry matter production and density of grasses, NSC rangelands appeared to be unstable. Results indicate that NSC facilitates the development of a dense woody recruitment layer that counteracts a favorable grass layer development. We conclude that SC is conditionally more effective in restoring a relatively stable and desirable bush-grass ratio for commercial farming purposes, whereas NSC increases the risk of vegetation transition back to a bush-dominated state. While essential in combination with both treatments, NSC demands an increased effort of follow-up control of woody recruits. [ABSTRACT FROM AUTHOR]

Three new pentacyclic triterpenoids: (20R)-3-oxolupan-30-al (1), (20S)-3-oxolupan-30-al (2) and (20R)-28-hydroxylupen-30-al-3-one (3), along with (20S)-3β-hydroxylupan-30-al (4), the latter previously described as a constituent of an epimeric mixture, were isolated from Acacia mellifera. In addition, the known metabolites 30-hydroxylup-20-(29)-en-3-one (5), 30-hydroxylup-20-(29)-en-3β-ol (6), atranorin, methyl 2,4-dihydroxy-3,6 dimethyl benzoate, sitosterol-3β-O-glucoside and linoleic acid were found in the analyzed plant species for the first time. The structures of the new metabolites were elucidated by extensive spectroscopic analyses and their relative stereochemistry was determined by NOESY experiments. The new metabolite 3 exhibited significant cytotoxic activity against the NSCLC-N6 cell line, derived from a human non-small-cell bronchopulmonary carcinoma.

A study on the population structure and abundance of the Grant's gazelle (Gazella granti Brooke, 1872) was carried out in the plains of Nechisar National Park, Ethiopia during November, 2008 - April, 2009. Distance sampling based on line-transect method was used to estimate the populations of the Grant's gazelles. Habitat association was assessed based on the abundance of herds or individuals observed in different habitats. The estimated population of Grant's gazelle in the study area was around 2100 heads. The population density was 10.5 ± 3.2 km-2. The mean herd size was 3.65 individuals, including the territorial male, females and fawns. The age ratio of adult to fawns was 1:0.22. The age structure of Grant's gazelles was 82.5% adult, 12.5% juvenile and 4.8% fawn. The sex ratio of adult male to adult female was 1:2, with a sex structure of 28.25% male, 54.25% female and 17.3% immature young. The grassland habitat ranked higher in the abundance of gazelles (n = 100, 67.1%) than shrubland (n = 49, 32.8%), indicating higher association of them with the grassland habitats of the Nechisar plains. Chrysopogon ucheri, Cenchrus ciliaris, Ischaemum afrum, Themeda triandra, Pennisetum mezianum, Brachiaria serata, Acacia mellifera, Acacia oerfota, Acacia brevispica and Dichrostachys cinerea were the major plants consumed by gazelles. [ABSTRACT FROM AUTHOR]

Dual-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. [ABSTRACT FROM AUTHOR]

Oral 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 anAcacia-dominated bush-land.Pelil(Acacia nubica),talamogh(Acacia mellifera), oranyua(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 asabrute(Brachiaria deflexa,Setaria homonyma) orpuyun(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. [ABSTRACT FROM AUTHOR]

Bush thickening is a major concern to farmers of arid and semi-arid rangelands; reactive intervention remains the norm. Here we compared some of the short-term ecological implications of chemical and physical removal of the bush encroacher Acacia mellifera in the central Highland savanna of Namibia. We selected 21 invaded sites, 7 had been chemically cleared, 7 had been physically cleared and 7 had never been cleared. From each site, we recorded grass species composition, as well as the densities of A. mellifera , the undesired perennial shrub Pechuel-loeschea leubnitziae and a non-targeted tree Acacia erioloba , 24–30 months post-treatment. We fitted one-way ANOVA models to test for the effect of treatment on grass species richness and density of targeted and non-targeted tree species. A canonical correspondence analysis was used to determine how treatment affected grass species composition. While both treatments reduced the density of the bush encroacher, P. leubnitziae effectively replaced A. mellifera in chemically treated sites, where die-back presumably happened faster and nutrient and water competition decreased more rapidly. In such sites, perennial grass species were effectively outcompeted by P. leubnitiziae . [ABSTRACT FROM AUTHOR]

Abstract: Savanna rangelands worldwide are threatened by shrub encroachment, i.e. the increase of woody plant species at the cost of perennial grasses, causing a strong decline in the productivity of domestic livestock production. Although recent studies indicate that fire might be of great importance for semi-arid and arid savanna dynamics, it is largely not applied in the management of semi-arid rangelands especially with regard to woody plant control. We used the eco-hydrological savanna model EcoHyD to simulate the effects of different fire management strategies on semi-arid savanna vegetation and to assess their long-term suitability for semi-arid rangeland management. Simulation results show that prescribed fires, timed to kill tree seedlings prevented shrub encroachment for a broad range of livestock densities while the possible maximum long-term cattle densities on the simulated semi-arid rangeland in Namibia increased by more than 30%. However, when grazing intensity was too high, fire management failed in preventing shrub encroachment. Our findings indicate that with regard to fire management a clear distinction between mesic and more arid savannas is necessary: While the frequency of fires is of relevance for mesic savannas, we recommend a fire management focussing on the timing of fire for semi-arid and arid savannas. [Copyright &y& Elsevier]

An online decision support system derived from research and expert knowledge was developed for arid rangeland management in central Namibia. The expert system emphasises the control of bush thickening and is divided into three forms of decisions: adaptive, reactive and ongoing good management. Adaptive decisions are mostly related to periods of protracted high rainfall, as this is a critical window both in terms of a hazard (transition to bushy thickened state if no fire is applied) and opportunity (transition back to an open savanna if fire is applied). Currently, the expert system uses wiki technology, as this allows a high level of interaction between user and administrator. The expert system includes embedded links to photographs and additional information. It allows easy updating of the knowledge base. An additional booklet was also developed, since access to computers and the internet is still limited. Although the evaluation of the expert system will be determined partly by its acceptance by rangeland managers, we adhered to many of the critical success factors relating to decision support systems in its development. The paper discusses some key strategies for the success of this and similar decision support systems for improved rangeland management in the future. [ABSTRACT FROM AUTHOR]

Abstract: The proliferation of woody plant species on savanna rangelands (i.e. bush encroachment) degrades rangeland quality, thereby threatening the biodiversity conservation effort as well as pastoral farming. Hyperspectral remote sensing offers possibilities for discriminating encroaching bush species in support of management of semi-arid savanna rangelands. As a preliminary step towards establishing a spectral library of common encroaching species on savanna rangelands, the effect of canopy leaf cover, background dry soil and grass on the spectral profiles of the common encroaching species Acacia karroo, Acacia mellifera, Acacia tortilis and Dichrostachys cinerea was analysed. A sample of healthy mature plants in prime, full leaf condition was utilised at an encroached rangeland in Mokopane, South Africa. The spectral signatures were collected in-situ, using a field spectrometer pointed above the sample specimen canopies. The canopy and canopy background variables tended to modify the reflectance of the encroaching bush species in the near infrared (800–1300 nm) in which they were spectrally most separable. Canopy background dry grass tended to increase near infrared reflectance, while dry soil tended to reduce the spectral contrast among the species. These effects were reduced by high leaf content. In a thicket canopy structure, the overall reflectance tended towards the spectral profile of the more dominant species. [Copyright &y& Elsevier]

ABSTRACT Seasonal availability of water is a key controlling factor in semi-arid savanna vegetation structure, function and interactions. Understanding of woody plant interactions with grasses in savannas has long been underpinned by Walter's two-layered niche differentiation hypothesis that postulates that grasses and trees source water from different depths. The Walter hypothesis persists in the literature, despite contrary evidence and a lack of quantitative empirical tests of the theory. We conducted a greenhouse experiment to determine the following: (1) whether tree seedlings and grasses obtain water from different depths on rocky and sandy soils; (2) whether interspecific competition affected tissue water content of clipped grasses; and (3) the influence of repeated grass clipping on soil moisture. Grass competition significantly reduced tree seedling rooting depth on both rocky and sandy substrates. Trees had significantly longer roots on rocky substrates than on sandy substrates for all combinations (trees only, trees with unclipped grasses and trees with clipped grasses). Results indicated a three-tier soil moisture depletion pattern, with a top layer (15 cm) exclusively exploited by grasses, an intermediate zone (25-35 cm) utilised by both grass and tree seedling roots and deeper subsoil exclusively tapped by tree seedling roots. Our results are consistent with Walter's hypothesis, but we distinguished between three rather than two layers of tree and grass root interactions in acquiring soil moisture. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Seed production and seedling survival are under-researched in savannas. We investigated these in a population of a major thickening species, Acacia mellifera, in an arid Namibian savanna over a nine year period (late 1998–early 2007) We asked the following questions: (i) How does viable seed production vary with rainfall and tree size, (ii) when does seed germination occur, (iii) is the seed bank of A. mellifera persistent, and (iv) how do competitive interactions with established trees influence recruitment of A. mellifera seedlings? Seed production was highly correlated with annual rainfall. In dry years, there was no viable seed production. En masse seed production only occurred in exceptionally high rainfall years, and was strongly correlated with size among trees >2 m tall. Seed predation was low. Seedlings only emerged directly after en masse seed production, suggesting ephemeral seed banks. Three times more seedlings emerged per m2, but seedling survival was five times less, under trees than away from trees, indicating strong competition for water with established trees. Seed production is a recruitment bottleneck in this species. Recruitment requires at least two consecutive seasons of favourable rainfall, and is highly episodic in arid savannas. [Copyright &y& Elsevier]

Aims: Coexistence of trees and grasses in nutrient-poor arid savannas may result in competition for soil N. While grasses may be more effective than woody plants in acquiring N from the soil, some leguminous woody species rely on N fixation. We assessed the role of N fixation in the N-budget of Acacia mellifera seedlings by varying N supply and grass competition. Methods: The contribution of N fixation to the N-budget of Acacia mellifera seedlings with varying N supply and grass competition was determined by measuring growth, nutrient concentrations, and N values. Results: Tree seedlings were 4-fold taller and had 20-fold more biomass in the absence of grass. Tree foliar δN was lower with (−0.25 ± 0.2‰, n = 9) than without grasses (5.2 ± 0.1‰, n = 64). The contribution of N-fixation to the N budget decreased with increasing N supply. Greater reliance on N-fixation by trees in the presence of grasses did not result in greater biomass accumulation or tissue [N] relative to tree seedlings grown without grass competition. Tree seedlings competing with grass had significantly more negative δC (−29.5 ± 0.6‰) than seedlings without grass competition (−28.8‰ ± 0.5‰). Conclusions: Induction of N-fixation by grass may have resulted from competition for nutrients. N-fixation enables tree seedlings to compensate for limited soil N and survive grass competition at a critical and vulnerable developmental stage of germination and establishment. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the role of fire in controlling bush thickening in arid savannas. Three controlled fires were initiated to investigate the responses of planted seedlings, saplings and mature shrubs. The stem diameters of seedlings, saplings and mature shrubs prior to the fire were measured. Other dimensions of the saplings and mature shrubs such as leaf mass were also estimated. The intensity of each fire was estimated. Fire temperatures adjacent to seedlings saplings and mature shrubs were measured using fire paints on steel plates. All three fires were moderately hot. One year after each fire, the mortality of seedlings in the fire treatments was very high (97.1–99.3%) and significantly greater than in adjacent controls (16.1–51.6%). Mortality and topkill of saplings and mature shrubs were negatively related to stem diameter. Fire temperature did not significantly affect mortality and topkill in most cases. Surviving saplings showed a much greater resprout response, relative to pre fire size, than larger shrubs and trees. Our results suggest that fire is crucial in interrupting the transition from open grassy savanna to thicket in arid savannas. Managers who prevent fires at this stage are likely to experience bush thickening in the future. [Copyright &y& Elsevier]

An in vitro ruminal gas production study was conducted to assess the effect of yeast supplementation on rumen fermentation of tanniniferous tropical browse mixtures prepared by mixing Berchemia discolor with Acacia brevispica, Acacia elatior, Acacia mellifera, Balanites aegyptiaca, Grewia bicolor or Zizyphus mucronata in a 1:1 dry weight ratio. The six browse mixtures were incubated with buffered rumen fluid alone or supplemented with dried Japanese Sake yeast (JSY) or polyethylene glycol (PEG). Ruminal gas production characteristics were evaluated using the Gompertz equation. The JSY addition increased gas production volume ( P < 0.05) and numerically increased the maximum gas production rate constant. Time to reach the maximum gas production rate was shortened by PEG addition as compared to the JSY and control treatments. It is possible that JSY promoted the rumen microbial activity in addition to forming complexes with tannins thereby upgrading the in vitro ruminal digestion of tropical browse mixtures. [ABSTRACT FROM AUTHOR]

Tree-on-tree competitive interactions may be more important in affecting the distribution of the tree components of savannas than inter-specific competition with grasses. The presence of intraspecific competition is expected to negatively affect inter-tree spacing, individual size distributions and plant physiology as well as survival/mortality. In this field removal experiment on Acacia mellifera, one of South Africa's most common encroachers on nutrient-poor soils, the growth, water relations and mortalities of shrubs where all neighbouring woody competitors were removed (target) were monitored three times during each of three growing seasons. After 3 years, the nitrogen and carbon isotopic ratios of the study plants were analysed. Target shrubs benefitted from removal of neighbours, resulting in greater growth, less water stress, a relatively small degree of canopy dieback and reduced reliance on N fixation. Target shrubs grew by 25 ± 4% in height relative to 7 ± 4% for controls, with the targets suffering a maximum of <15% canopy dieback compared to up to 60% in the controls. Severe environmental stress is known to affect neighbour interactions among shrubs and competition may constrain shrub sizes and avoid density-dependent mortality. In contrast, release from competition in our study may have allowed greater growth of target plants, increasing their total evapo-transpirational leaf surface areas and leaving them vulnerable to drought and water stress. Intratree competition on shallow nutrient-poor soils in savannas may thus aid the persistence of bush encroachment by regulating the sizes of individual shrubs below the threshold of drought vulnerability. [ABSTRACT FROM AUTHOR]

Abstract: We examined the impact of shrub–shrub interactions and soil type (rocky or sandy) on growth and spatial distribution of the two savanna shrub species Tarchonanthus camphoratus and Acacia mellifera. To explore plant interactions, we compared the size of juvenile and mature T. camphoratus shrubs between different locations (under the subcanopy of A. mellifera and in the open). Juvenile T. camphoratus shrubs had similar sizes regardless of location; however, in rocky soil, mature shrubs in the open were larger than those near A. mellifera, implying an inter-specific competitive effect of A. mellifera on T. camphoratus. Juvenile T. camphoratus shrubs grew faster in the sandy than in the rocky area. Furthermore, we used the Wiegand–Moloney O-ring statistics to explore the spatial distribution of T. camphoratus. T. camphoratus showed spatial aggregation, but in the rocky area T. camphoratus juveniles were positively associated with A. mellifera (indicating facilitation as the pattern-creating process), whereas in the sandy area they were positively associated with mature T. camphoratus shrubs (indicating seed dispersal as the pattern-creating process). T. camphoratus exhibited encroachment potential in the sandy area. We showed how spatial pattern analysis can help to explore processes determining woody plant spacing and recommend its further use. [ABSTRACT FROM AUTHOR]

Bush encroachment is a form of land degradation prominent worldwide, but particularly present in semi-arid areas. In this study, we mapped the spatial distribution of the two encroacher species, Acacia mellifera and Acacia reficiens, in Central Namibia, based on their different phenological behavior. We used constrained principal curves to extract a one dimensional gradient of phenological change from two hyperspectral images taken in different seasons. Field measurements of species composition and cover values were statistically related to bi-temporal differences in hyperspectral vegetation indices in a direct gradient analysis. The extracted gradient reflected the relationship between species composition and cover values, and the phenological pattern as captured by the image data. Cover values of four dominant plant species were mapped and species responses along the phenological gradient were interpreted. [ABSTRACT FROM AUTHOR]

The article discusses study of the Spinescent East African savannah acacias. Topics discussed include the relative bark thickness (RBT) is measured of allocation to fire defence, species of acacia which include acacia xanthophloea, acacia mellifera, and acacia drepanolobium, and analysis on the benefit of bark and thorns to environment.

Aim Evidence is accumulating of a general increase in woody cover of many savanna regions of the world. Little is known about the consequences of this widespread and fundamental ecosystem structural shift on biodiversity. Location South Africa. Methods We assessed the potential response of bird species to shrub encroachment in a South African savanna by censusing bird species in five habitats along a gradient of increasing shrub cover, from grassland/open woodland to shrubland dominated by various shrub species. We also explored historical bird species population trends across southern Africa during the second half of the 20th century to determine if any quantifiable shifts had occurred that support an ongoing impact of shrub encroachment at the regional scale. Results At the local scale, species richness peaked at intermediate levels of shrub cover. Bird species composition showed high turnover along the gradient, suggesting that widespread shrub encroachment is likely to lead to the loss of certain species with a concomitant decline in bird species richness at the landscape scale. Finally, savanna bird species responded to changes in vegetation structure rather than vegetation species composition: bird assemblages were very similar in shrublands dominated by Acacia mellifera and those dominated by Tarchonanthus camphoratus. Main conclusions Shrub encroachment might have a bigger impact on bird diversity in grassland than in open woodland, regardless of the shrub species. Species recorded in our study area were associated with historical population changes at the scale of southern Africa suggesting that shrub encroachment could be one of the main drivers of bird population dynamics in southern African savannas. If current trends continue, the persistence of several southern African bird species associated with open savanna might be jeopardized regionally. [ABSTRACT FROM AUTHOR]

Abstract: Ethnopharmacological relevance: Acacia mellifera (Vahl) Benth (Leguminosae) is a subtropical medicinal plant that is widely used in traditional African medicines against various diseases such as pneumonia and malaria. Aim of the study: The present study was performed to evaluate the antimicrobial effects of extracts from the stem bark of Acacia mellifera. Materials and methods: The extracts were examined for antibacterial and antifungal activity using the disc-diffusion method against bacterial strains: Streptococcus pneumoniae (ATCC 25923), Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 35218), Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) and fungal strains Candida albicans (ATCC 90028), Candida krusei (ATCC 6255), Cryptococcus neoformans (ATCC 6603) and clinical isolates of Microsporum gypseum and Trichophyton mentagrophytes. Results: Some of these extracts were found to be active against some bacterial and fungal strains and were further fractionated to give 12 pure compounds. The methanolic and methanol:dichloromethane (1:1) extracts exhibited antibacterial and antifungal activity. The two were active against Staphylococcus aureus (ATCC 25923), Microsporum gypseum, and Trichophyton mentagrophytes. Activity guided fractionation led to isolation of two active compounds: 3-(Z)-cis coumaroylbetulin and 30-hydroxylup-20 (29)-en-3β-ol which were against Staphylococcus aureus (ATCC 25923), Microsporum gypseum, Trichophyton mentagrophytes and Pseudomonas aeruginosa (ATCC 27853). Conclusions: These results may partly explain and support the use of Acacia mellifera stem barks for the treatment of infectious diseases in traditional Kenya medicine. [Copyright &y& Elsevier]

The feeding value of five browse foliages ( Acacia brevispica, Acacia mellifera, Berchemia discolor, Zizyphus mucronata and Maerua angolensis) grown in semiarid area of Kenya were evaluated. Their chemical composition including polyphenolics and in vitro gas production characteristics were determined. The biological activity of the polyphenolics was assessed as the increases in gas production profiles and in vitro true dry matter (DM) and organic matter (OM) digestibility after in vitro incubation with or without addition of polyethylene glycol (PEG) as a tannin binding reagent. The intake and palatability ranking of the browse foliages by goats and sheep were also investigated. The browse foliages had variable crude protein content (149.5–248.6 g/kg DM) and variable content of neutral detergent fiber (205.1–424.0 g/kg DM). The content of total extractable tannins was generally low (2.4–34.8 g/kg DM). At 24 h of incubation, Z. mucronata produced the highest gas volume, while after 48 h of incubation, B. discolor produced the highest gas volume. M. angolensis had the least gas production potential within the browse foliages. Addition of PEG increased gas production except in A. mellifera and M. angolensis. However, PEG addition did not have any significant effect on in vitro true DM and OM digestibility except in B. discolor, which decreased. The rank order of preference (highest to least) for goats was A. brevispica, Z. mucronata, B. discolor, A. mellifera and M. angolensis while the rank order of preference for sheep was A. brevispica, B. discolor, A. mellifera, Z. mucronata and M. angolensis. The goats had higher intakes of all the browse foliages than sheep. The result of this study highlights the higher feeding value of the browse species as supplemental feed with low quality basal diet with both of animal species except M. angolensis. [ABSTRACT FROM AUTHOR]

Bird community diversity was assessed in semi-arid savanna in the Northern Cape province of South Africa and related to vegetation diversity and foliage height diversity. As this is an area in which shrub encroachment is common, the effects of shrub or bush encroachment on bird species diversity were specifically addressed. An experiment in which the dominant encroaching species, Acacia mellifera, was removed from ten 1 ha plots was used and compared with ten controls. A strong positive association with foliage height diversity was shown. No effect of experimental removal of the dominant encroacher, A. mellifera, on bird species diversity or species richness was found. However, four species increased in relative abundance in cut plots and two species decreased in relative abundance in these plots. [ABSTRACT FROM AUTHOR]

Abstract: Coexistence of trees and grasses in savannas should be possible if competition between the woody and the grassy components is less intense than the competition within each component. Although several studies have investigated competition between trees and grasses, little is known about tree–tree interactions. We used a multi-proxy approach to examine the spatial pattern of Acacia mellifera and other savanna woody species in a semi-arid savanna in South Africa. Spatial analysis of the point patterns of young and reproductively mature shrubs detected decreasing aggregation with size/age over all spatial scales. This indicated the prevalence of competition although the overall spatial shrub pattern was aggregated. In contrast to point pattern statistics that detect changes only when competition has led to the death of the inferior competitor, we also applied methods identifying the competitive effect on sizes of individual trees. Competition should lead to a negative spatial autocorrelation in size, which we observed in half of the studied cases. Quantile regressions show that nearest-neighbour distance increased steeply with combined size of the target shrub and its neighbours indicating strong competitive effects. The medians of the distributions of maximum root lengths of A. mellifera, of the scale of regular patterns, and of negative autocorrelations were not significantly different, suggesting that overlapping root systems mediate competitive interactions. A competitor removal experiment did not lead to increased shrub sizes, which may be due to the limited duration of the experiment. From the nearest neighbour and autocorrelation analyses, we conclude that competition had a strong impact on growth rates of savanna woody species. Competition-induced mortality only becomes obvious when analysing the shift towards less aggregated spatial patterns when shrubs become reproductively mature. As the overall clustered spatial pattern masks the perceptible effect of competition, a time component should always be included in spatial pattern-based inference of competition. [Copyright &y& Elsevier]

Many mechanisms have been suggested to explain the coexistence of woody species and grasses in savannas, yet, evidence from field studies and simulation models has been mixed. Shrub encroachment is an ecological and economic problem in savannas worldwide which generally is attributed to overgrazing. Patch-dynamics is a new mechanism explaining tree-grass coexistence and the natural occurrence of shrub encroachment in savannas. A patch-dynamic savanna consists of patches in which cyclical succession between grassy and woody dominance proceeds spatially asynchronously. The spatially explicit, individual-based patch-scale simulation model SATCHMO was developed to investigate cyclical succession in the paradigm of patch-dynamics for arid and semi-arid savannas. SATCHMO is designed to capture within-patch shrub population dynamics based on a grid of 51m side length and a resolution of 10cm. The model shrub characteristics were derived from Acacia mellifera, the main encroaching species in African savannas. The aim of SATCHMO is to give a detailed small-scale understanding of above- and belowground growth, competition, and mortality of savanna woody plants and the influence of precipitation and fire on patch transition frequencies, shrub growth rates, and shrub size frequencies. With SATCHMO, we want to identify the conditions leading to cyclical successions in general and shrub encroachment in particular. Soil moisture is the most important parameter in SATCHMO influencing growth, reproduction, and mortality of shrubs and grass tufts, and that mediates competition. To acknowledge the importance of belowground interactions in savannas, shrub root growth and competition are modelled spatially explicitly. The model output was successfully validated with morphometrical and spatial data from the field site in the South African Kalahari thornveld and with recent literature data on savanna woody species cover. Global sensitivity analysis with Latin hypercube sampling shows that soil moisture is the most important driver of shrub cover dynamics in semi-arid savannas. [Copyright &y& Elsevier]

1. Patch dynamics is a new, potentially unifying mechanism for the explanation of tree-grass coexistence in savannas. In this scale-explicit paradigm, savannas consist of patches in which a cyclical succession between woody and grassy dominance proceeds spatially asynchronously. The growing ecological and economic problem of shrub encroachment is a natural transient phase in this cycle. 2. An important step towards understanding patterns at the landscape scale is achieved by investigating mechanisms at a smaller scale. We developed the spatially explicit individual-based simulation model SATCHMO to test the null hypothesis that cyclical succession cannot emerge from a realistic patch scale simulation model of the population dynamics of savanna woody species. 3. We calculated the partial temporal autocorrelation coefficient for 100 simulated time series of shrub cover over 500 years for time lags of up to 200 years to establish the existence and duration of successional cycles. We found a significant positive autocorrelation indicating the existence of cycles with a typical duration of about 33 years. 4. The shrub size frequency distributions over the course of a cycle showed shifts from dominance of small shrub sizes towards larger sizes during the increasing phase of a cycle and the reverse in the declining phase. This supports the three phase explanation as follows: (i) an initial phase when spatially and temporally overlapping favourable conditions lead to mass recruitment of shrubs; (ii) a build-up phase when the shrub cohort grows; and (iii) a break-down phase when increased competition due to crowding and unfavourable conditions lead to the break-down of the shrub cohort. The frequency distribution of shrub age at death over 10 simulations was also in agreement with this explanation. 5. We investigated the relationship between shrub cover, annual precipitation and time-lagged shrub cover to identify the driver of the cyclical successions. More than 90% of the variation in shrub cover was explained by shrub cover of the previous year, precipitation, and their interaction. 6. With the demonstration of precipitation-driven cyclical succession at the patch scale, we show that the mechanistic, temporal component of patch dynamics can be used to explain tree-grass coexistence in semi-arid savannas. [ABSTRACT FROM AUTHOR]

Abstract: The phenology of three dominant and economically important tree species; Acacia erioloba, Acacia luederitzii and Acacia mellifera, all widespread in the Kalahari in Botswana, was studied at Tsabong (25°56.65′S, 22°27.72′E) and Maun (20°09.60′S, 23°46.63′E) receiving 300 and 463mm annual rainfall, respectively. The main aims were to investigate how possible environmental cues influence timing and development of phenophases and whether different tree species have different seasonal responses to these cues. Likely effects of climatic changes on phenological development patterns were also considered. All three species studied had generally comparable seasonal responses irrespective of the mean annual rainfall at each site, but differed in the timing of certain phenophases. Both A. erioloba and A. mellifera flowered at the end of the cool dry season. Acacia erioloba produced new leaves simultaneous with flowers while A. mellifera produced fully developed fruits before leaves. On the other hand, A. luederitzii produced leaves and flowered after rain and well into the growing season, with leaves appearing before the flowers. For A. erioloba and A. mellifera, temperature and daylength appeared to be the most probable phenological cues, while in the case of A. luederitzii, it was rainfall. All species produced lower amounts of certain litter components during the year of lower rainfall at the Tsabong site, affecting fodder availability. Livestock was observed feeding on newly emerged flowers, leaves and new twigs, relieved from scratching the ground for dry grass, fallen leaves and pods. Other studies have also observed new growth to provide valuable fodder in the dry season and drought periods, making phenological timing economically crucial. Any shift in climatic factors that affect this timing may have detrimental consequences. Drought is the best-known example of an extreme shift. There is need for more information on the likely extent of other shifts and possible effects in vulnerable areas such as the Kalahari in the face of changing environmental and climatic conditions. [Copyright &y& Elsevier]

Moisture, nutrients, fire and herbivory are the principal factors governing tree–grass cover ratios of savannas. We investigated tree ( Acacia mellifera) recruitment after fire and under conditions of maximum-recorded rainfall, nitrogen addition and grazing in a completely-crossed field experiment. We employed a similar garden experiment with the exception of the fire treatment. Tree germination in the field was extremely low, probably due to below-average natural rainfall in plots that only received natural rain, and insufficient watering frequency in irrigated plots. Due to low germination in the field experiment, no treatment significantly affected tree recruitment. In the garden experiment, frequent watering, nutrient control (i.e. no nitrogen addition) and grazing enhanced tree recruitment with significant interactions between rain, nitrogen and grazing. We infer that above-average rainfall years with frequent rainfall events are required for mass tree recruitment. Grass defoliation makes space and resources available for tree seedlings. Nitrogen enrichment increases the competitive ability of fast-growing grasses more than that of the N2-fixing tree component. In contrast to conventional wisdom that grazing alone causes encroachment, we suggest that there are complex interactions between the above-mentioned factors and ‘triggering’ events such as unusually high rainfall. [ABSTRACT FROM AUTHOR]

Abstract: Recent extensive harvesting of large, often dead Acacia trees in arid savanna of southern Africa is cause for concern about the conservation status of the arid savanna and its animal community. We mapped vegetation and nests of the Black-tailed Tree Rat Thallomys nigricauda to assess the extent to which the rats depend on particular tree species and on the existence of dead, standing trees. The study was conducted in continuous Acacia woodland on the southern and eastern edge of the Kalahari, South Africa. Trees in which there were tree rat nests were compared with trees of similar size and vigour to identify the characteristics of nest sites. Spatial analysis of tree rat distribution was conducted using Ripley''s-L function. We found that T. nigricauda was able to utilize all available tree species, as long as trees were large and old enough so that cavities were existing inside the stem. The spatial distribution of nest trees did not show clumping at the investigated scale, and we therefore reject the notion of the rats forming colonies when inhabiting continuous woodlands. The selection of a particular tree as a nest site was furthermore depending on the close proximity of the major food plant, Acacia mellifera. This may limit the choice of suitable nest sites, since A. mellifera was less likely to grow within a vegetation patch containing a large trees than in patches without large trees. [Copyright &y& Elsevier]

Abstract: This paper provides an analysis of the physical and chemical characteristics of cyanobacterial soil crusts in the Molopo Basin, South Africa. It details the influence that soil type, livestock disturbance and shrubs have on the spatial distribution of crusts. Four morphologically distinct cyanobacterial crusts were identified and crust cover ranged from 24% to 55%. Crust cover was significantly higher and characterized by darkened type 3 and 4 crusts on Ironstone soils compared to Kalahari Sand. More frequently disturbed sites had the least crust cover and had predominantly type 1 and 2 crusts. Type 3 and 4 crusts are more common on the less disturbed sites and under the canopies of Acacia mellifera where soils are protected from livestock disturbance. Total nitrogen concentrations were significantly higher in crusts compared to unconsolidated soil. There is also a strong correlation between the pH and NH4 +-N concentrations in crusts and the soil immediately below the crust, suggesting that crusts have an influence on some of the properties of the underlying soil. If the A. mellifera can utilize additional nitrogen from crusts it may provide a competitive advantage to their establishment in formerly grass-dominated grazing lands. [Copyright &y& Elsevier]

Intensive grazing of Kalahari rangelands has led to woody plant encroachment, notably ofAcacia melliferaandGrewia flava. The mechanisms causing this process, and the ecological stability of woody plant encroached ecosystems, remain uncertain. Past studies suggest that canopy–soil relations may enhance woody plant competitive dominance. This study aims to investigate one element of this ecological change by examining the spatial distribution of cyanobacterial soil crusts in two vegetation sub-habitats at sites of different disturbance. Crust burial by litter was also assessed to analyse the dynamics of canopy–crust relations. Our results show there is enhanced cyanobacterial crust cover underA. melliferacanopies and that unlikeG. flavacanopies, the crust cover remains underA. melliferaeven at highly disturbed sites. This canopy–crust association suggestsA. melliferaencroachment exhibits intrinsic resilience because of the crusts ability to stabilize the soil surface and increase nutrient retention. Crust burial by litter that accumulates under larger woody plants restricts crust development under canopies. Disturbance restricts crust development in plant interspaces and underG. flava. These two mechanisms combine to restrict crust development to an observed 40% threshold, with nonlinear models required to explain spatial patterns of crust dynamics. [ABSTRACT FROM AUTHOR]

Abstract: The study was conducted in a semi-arid savanna of South Africa, dominated by an almost pure stand of Acacia mellifera subsp. detinens (Black Thorn). Due to its invasive habits and suppression of the herbaceous layer, this woody species is viewed by land owners as a serious threat. Clearing of all A. mellifera trees in order to restore the production potential of the herbaceous layer is thus a well-established practice. In view of possible beneficial effects of A. mellifera, a study was undertaken with the objective of quantifying differences in soil nutrient status under A. mellifera canopies (canopied subhabitat) in comparison to the open areas (uncanopied subhabitat). The results of the study confirmed the existence of differences in the soil nutrient status between the various subhabitats, which occurred in a specific spatial gradient from the stem base of the plants towards the open, uncanopied areas. These differences were statistically significant () for total N, % organic matter and Ca, with the highest values recorded in the area surrounding the stem base. Though statistically non-significant () the P and K contents, and to a lesser extent Mg, were also higher under the tree canopies, while pH was lower. No differences () were established for Na. Some notable differences to similar studies in other areas were established, of which the reduction of soil pH is an example. The practical significance of these results in terms of land management practices is discussed, which will invariably necessitate a change in attitude of land owners in their approach to the management of A. mellifera. [Copyright &y& Elsevier]

One new and eight previously described lupane-type metabolites were isolated for the first time from Acacia mellifera (Leguminosae). Based on spectral analyses, the structure of the new compound was elucidated as 28-hydroxy-3-oxo-lup-20-(29)-en-30-al (1), while the known compounds were identified as 3-oxo-lup-20-(29)-en-30-al (2), 3-hydroxy-lup-20-(29)-en-30-al (3), 28-hydroxy-lup-20-(29)-en-3-one (4), lupenone (5), lupeol (6), betulin (7), betulinic acid (8), and betulonic acid (9). Metabolites 2, 3, and 4 are reported for the first time in the Leguminosae family. The cytotoxicity of the isolated metabolites was evaluated on the NSCLC-N6 cell line, derived from a human non-small-cell bronchopulmonary carcinoma. Compounds 1 and 3 exhibited significant levels of activity. [Copyright &y& Elsevier]

For a typical encroacher tree of the thornbush savanna, we studied the responses of water consumption to changes in soil water availability within 80 cm depth, vapor pressure deficit (VPD), and global radiation. Therefore, we monitored the sap velocities of Senegalia mellifera trees over 2 years in a maximum of 20 stems (6–15 plant individuals) per measurement period on a site in central Namibia. For this water-restricted ecosystem we aimed to understand the role of an encroacher tree on soil water dynamics and potential groundwater recharge. At the day-to-day scale, soil water was the primary driver of cumulative daily sap velocities (Q n-day). In the dry season, Q n-day decreased with increasing soil drought. Rainy seasons triggered multiple sapflow phases, initiated by soil-wetting rain events and associated with increase of soil water. Maximum attainable Q n-day increased with VPD and radiation. We hypothesize a 3-stage response of tree water use to soil water tension (SWT): (1) SWT < pF 2.6–2.7: soil water is optimal for transpiration; (2) pF 2.6–2.7 < SWT < pF 3.2–3.7: transpiration decreases with soil drought; (3) SWT > pF 3.2–3.7: trees minimize transpiration. Our findings contribute to the understanding of tree–grass coexistence in savannas. The responses of tree water use to soil water within 80 cm depth indicate that S. mellifera exploits the same depths as grasses, in contrast to the classic hypothesis of vertical niche differentiation. • The tree–grass coexistence of Senegalia mellifera in savannas is related to differences in timing of plant productivity. • Across days, soil water availability is the dominant controlling factor of water consumption by S. mellifera. • During daytime, water consumption of S. mellifera is controlled by global radiation and to a lesser extent by VPD. • During the rainy season, after the leaves have emerged, S. mellifera responds within one day to rain that wet the soil. • S. mellifera takes up water from the same soil depth as grasses. [ABSTRACT FROM AUTHOR]

Focuses on the study of the ecology of acacia mellifera, seyal and balanites aegyptiaca in relation to land clearing. Investigation of land clearing methods in acacia mellifera thicket; Discussion of land clearing methods in acacia mellifera thicket; Relationship between the vegetation and grass fires.

The article discusses a study on the soils and vegetation of Fung area located at the East Central Sudan. The author mentions that Fung region consists of tropical and continental climate and topographically, it has monotonous alluvial plain. The soils of the region are form from the clay deposit of Abyssinian origin. The author describes that the principal soils of the region consists of montmorillontic clay and they are also non-saline. The region's vegetation includes Acacia mellifera-Cadaba rotundifolia thicket and bushland, Acacia seyal-A. fistula-Balanites aegyptiaca woodland and broad-leaf deciduous woodland.

The article provides information about the condition of vegetation in the northern coastal plain and hills of Jedda, Saudi Arabia, which extends into the eastern slopes of the Red Sea mountains. It particularly discusses the characteristics of rainfall in the region, and describes the main topographical features of the vegetation area. The eight plant associations of the region's vegetation were also described. Those associations include the Olea-Tarchonantghus association, the Acacia mellifera association, the associations of the coastal plain, and the associations of halophytes.

We isolated 11 polymorphic microsatellite markers from Acacia mellifera, a savannah woodland tree in sub-Saharan Africa and southern Arabia. The loci were screened for polymorphism using 48 Kenyan individuals. Allelic diversity ranged from three to 19 per locus and the polymorphic information content varied from 0.287 to 0.893. These loci will be useful in studies of genetic structure, gene flow and breeding systems. [ABSTRACT FROM AUTHOR]

Presents an abstract of the study `Endophytic fungi occurring in Acacia mellifera ssp. detinens in Namibia,' by A.K. Vermeulen, G. Holz et al presented at the 32nd annual congress of the South African Society for Plant Pathology held at the Aventura Vaal Spa, Christiana, South Africa from January 23-26, 1994.