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• Oral acute and sub-acute toxicities of Acacia sieberiana were evaluated in rats. • No major signs of toxicity were observed in the liver and kidneys. • Slight signs of toxicity were observed at a dose of 1000 mg/kg body weight/day. • Acacia sieberiana bark is harmless at lower dose. Acacia sieberiana DC. var. woodii or Vachellia sieberiana var. woodii (Burtt Davy) Kyal. & Boatwr. is a plant used in Cameroon to treat several diseases such as bilharzia, tapeworm, hemorrhage, rheumatism, gonorrhea, syphilis, ophthalmia, stomachache, urethral diseases, oedema, and diarrhea. The methanol extract of Acacia sieberiana leaves (ASL) has been reported previously for its antiproliferative activity towards several human cancer cell lines. This research aims to evaluate the acute toxicity and subacute toxicities of ASL. The acute toxicity was carried out according to established protocol. The crude extract (ASL) was administered orally to female rats at a single dose of 5000 mg/kg body weight (b.w.) and the animals were observed for any behavioral changes or mortality. In the subacute toxicity study, ASL was orally administered daily to male and female rats at different doses (250, 500, and 1000 mg/kg b.w.) for 28 days. During these treatment days, the animals were observed for any appearance of toxicity symptoms. Following the treatment period, animals were sacrificed for hematological, biochemical, and histopathology analysis. The acute toxicity study revealed neither behavioral disturbances nor death in rats. The lethal dose (LD 50) body weight was greater than 5000 mg/kg b.w. Subacute administration of ASL showed significant variations (P > 0.05) of body weight, the relative weight of organs, some hematological and biochemical parameters. Histopathological examinations showed no remarkable pathological changes on the kidney and slight cell lysis in the liver. This study shows that ASL is non-toxic, but that caution should be taken in case of the prolonged consumption of the botanical at a high dose (1000 mg/kg b.w.). [ABSTRACT FROM AUTHOR]

Acacia sieberiana is an ecological and economical important forest tree. The plant has poor germination due to dormancy; therefore, in vitro culture can provide a fast supply of plantlets and can be a basis for further biotechnology research. The effect of sodium hypochlorite, Murashige and Skoog (MS) medium, sucrose and cytokinin were investigated. The results indicated that all the treatments induced significant (P < 0.05) effects on germination and seedling development depending on their concentrations. Germinates free of contamination were established successfully with all the concentrations of sodium hypochlorite, however, the germination was reduced as the concentration increased. A higher germination rate of 98.3% was attained with full MS strength and 3% sucrose concentration. The highest germination percentage obtained was 100% with 2 mg/L thidiazuron. The maximum shoot length (13.5 cm) and seedling dry weight (0.49 g) were recorded on full MS medium while the maximum root length (13.4 cm) was obtained on ½ MS strength. However, when full MS medium augmented with 5% sucrose enhanced shoot length and dry weight to (14.2 cm) and (0.5 g), respectively. While the highest root length (10.2 cm) was obtained by 3% provided in full MS medium. Application of cytokinins improved the number of node and dry weight of seedlings to 6.9 nodes with 4 mg/L thidiazuron and 0.54 g by 2 mg/L benzyladenine. The present study describes the establishment of⅛ vitro seed germination and seedling growth system for A. sieberiana for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Woody plant encroachment in grasslands is a worldwide phenomenon. Despite many studies, the consequences of woody plant encroachment on sub-canopy vegetation and soil properties are still unclear. To better understand the impacts of trees on grassland properties we examined the following questions using a mountainous sub-tropical grassland of South Africa encroached by an indigenous tree, Acacia sieberiana as a case study: (1) Do trees increase sub-canopy herbaceous diversity, quality and biomass and soil nitrogen content? (2) Do large trees have a stronger effect than medium-sized trees on grass and soil properties? (3) Does the impact of trees change with the presence of livestock and position of trees in a catena? We studied grass and non-graminoid species diversity and biomass, grass quality and soil properties during the wet season of 2009. Nitrogen in grass leaves, soil cation exchange capacity and calcium and magnesium ion concentrations in the soil increased under tall Acacia versus open areas. Medium-sized Acacia decreased the gross energy content, digestibility and neutral detergent fibre of grasses but increased the species richness of non-graminoids. Tall and medium Acacia trees were associated with the presence of Senecio inaequidens, an indigenous species that is toxic to horses and cattle. The presence of livestock resulted in a decrease in herbaceous root biomass and an increase in soil carbon and leaf biomass of grass under Acacia. Tree position in the catena did not modify the impact of trees on the herbaceous layer and soil properties. For management of livestock we recommend retaining tall Acacia trees and partially removing medium-sized Acacia trees because the latter had negative effects on grass quality. [Copyright &y& Elsevier]

Abstract: Gully erosion and woody plant encroachment are frequently observed in grasslands worldwide. Gully erosion driven by water processes is usually affected by topography, land-use change and vegetation cover. We hypothesised that trees, through their potential link with overland and subsurface flow, may have an impact on gully extension. However, very few studies have simultaneously considered tree encroachment and gullies. We used aerial photographs to study Acacia sieberiana encroachment and gully erosion in a South African grassland (KwaZulu-Natal Province) for a period lasting 64years. At the catchment scale, results showed that acacias started invading after 1976 and transformed the grassland into a savanna with 9.45% of tree cover in 2009. Gully area increased by 3.9% in the last 64years and represented 12.76% of catchment area in 2009. Mean estimated sediment loss was 200Mgha−1 of gully y−1, indicating a high erosion rate mainly due to the collapse of gully banks after swelling and shrinking. Volumetric retreat rate (V) of 15 gully heads was correlated with drainage area (Drain.A) by a power function explaining 64% of the variance: V =0.02*Drain.A 0.83. A positive correlation between gully retreat rate and Acacia canopy area was measured between 2001 and 2009 when established tree encroachment was observed. These results, associated with the susceptibility of this soil to subsurface flow and the observation of pipe erosion systems in the field, showed that both surface and subsurface processes occur in this sub-humid grassland and that trees can be indirectly associated with increased gully erosion. [Copyright &y& Elsevier]

with many grasslands globally, the Highveld grasslands of South Africa are tree-less, despite having a climate that can support tree growth. Models predict that fire maintains these grasslands. The question arises as to why fire-tolerant savanna trees do not survive in these ecosystems? Savanna tree survival in mesic areas is restricted by demographic bottlenecks, specifically limitations to sapling-escape from fire. It was hypothesised that ancient highly leached soils from grassland areas would prevent saplings from growing fast enough to escape the fire-trap. Growth rates of savanna tree seedlings ( Acacia karroo Hayne and Acacia sieberiana Burtt Davy) were measured in a common garden experiment using soils from ten sites collected along a savanna-grassland continuum. Soils from grassland sites were relatively nutrient-poor compared to those from savannas with lower pH, and associated cations. A. sieberiana growth rates responded to pH and these nutrients, whereas A. karroo growth was less strongly linked to specific nutrients. Even so, both species accumulated more biomass when grown in soils from savanna sites compared to grassland sites. An exception was a low elevation low nutrient savanna site that resulted in poor growth, yet sustains high tree biomass in situ. Differences between growth in grassland and savanna soils were small. They may contribute to, but are unlikely to explain, the treeless nature of these grasslands. [ABSTRACT FROM AUTHOR]

The study evaluated the synergism between wheat bran and tanniferous feeds (dry meal or silage from pods of Acacia sieberiana) on intake and digestibility of various nutrients as well as weight gain in sheep fed a basal diet of veld hay (Cynodon dactylon). Dietary treatments comprised veld hay given ad libitum and supplemented with: 270 g of wheat bran (WB) alone (T1), 203 g of WB plus 83 g of silage (T2), 135 g of WB plus 165 g of silage (T3), 330 g silage without WB (T4) or 306 g of dry pods without WB (T5). The silage was prepared by mixing ground pods with water in a ratio of 40:60 (weight of pod:weight of water) and ensiling in 200-l drums for 35–45 days. Thirty young South African Merino sheep (15 males and 15 females), averaging 24 kg liveweight and 8 months of age, were blocked by sex and weight and within block, randomly distributed to the dietary treatments. A growth study was followed by a metabolism phase. All animals were slaughtered at the end of the trial to evaluate the weight of the dressed carcasses and some body organs. Faecal samples were examined at the beginning and at the end of the trial in order to evaluate the effect of tannins on endoparasites. Dry matter intakes for treatments 1, 2, 3, 4 and 5 were 1017, 1087, 1169, 1238 and 1214 g, respectively. Average liveweight gains (ADG) were 97, 114,114, 132 and 123 g in the same order. The addition of silage increased (P<0.01) hay and DM intake but had no effect (P>0.05) on liveweight gain and feed conversion efficiency. Increasing the levels of silage in the diet linearly (P<0.01) increased ADG. Sex did not influence intake or ADG. The digestibilities of DM, OM and detergent fibres as well as excretion of purine derivatives were similar (P>0.05) among treatments but the WB diet promoted higher N digestibility. The pod and silage diets increased (P<0.01) faecal N and lowered (P<0.05) urinary N excretion by sheep. N retention was similar among treatments. Carcass, liver and kidney weights were similar (P>0.05) among treatments and the organs had no lesions. The results show that combining WB and silage did not show significant synergism but condensed tannins present in the silage and pod supplements produced beneficial effects probably by forming tannin–protein complexes which by-passed the rumen and were digested at the lower segments of the gastro-intestinal tract. The results of the study have shown that the pods of Acacia sieberiana can constitute an important source of nitrogen to livestock and the liveweight gains are indications that, if legume pods are well managed, they can reduce weight loss in animals grazing low quality rangelands and enhance production. [Copyright &y& Elsevier]