Context:Salvadora persica L. (Salvadoraceae), Colophospermum mopane (J.Kirk ex Benth.) J. Léonard (Leguminosae) and Dichrostachys cinerea (L.) Wight & Arn. (Leguminosae) crude extracts are used by local farmers against many livestock infections with little or no side effects usually associated with synthetic antimicrobials. However, their efficacy has rarely been tested.Objective: These plants were tested for potential antibacterial activity against clinical isolates of Staphylococcus aureus ATCC33862 and Escherichia coli ATCC25922. Minimal inhibitory concentrations (MIC) of the crude plant extracts were determined.Materials and methods: Aqueous and methanol extraction of 100 g each of the bark of C. mopane, roots of D. cinerea and leaves of S. persica was done by placing the samples in 250 mL of either water or methanol. Nutrient broth was used as growth medium for the bacteria, and McFarland standard for bacterial standardization. 2,3,5-Triphenyltetrazoliumchloride (TTC) was the indicator salt. Each of the aqueous and methanol extracts (100 μL) was tested. Gentamycin and ampicillin were the controls.Results: MIC of aqueous extracts ranged from 1.03–14.6 mg/mL against S. aureus, and from 12.1–34.3 mg/mL against E. coli. Methanol extracts ranged between 5.31 and 9.64 mg/mL against S. aureus, and between 7.86 and 13.6 mg/mL against E. coli. Aqueous and methanol extracts of S. persica were significantly higher (p < 0.05) than C. mopane and D. cinerea.Discussion and conclusion:Colophospermum mopane, S. persica and D. cinerea exhibited antibacterial activity, with methanol extracts performing better than aqueous extracts, justifying use as ethnoveterinary medicine. Further study to isolate the active components should be pursued.

Anthropogenic alteration of an environment and other disturbance regimes may enable the expansion of some native species into new geographical areas, a phenomenon observed with Dichrostachys cinerea. Five D. cinerea invaded sites, each approximately one hectare in size were assessed for the effects of D. cinerea on native herbaceous species diversity, richness, basal cover, litter cover, top hamper and plant vigour. The same attributes were studied in five uninvaded sites adjacent to, and equal in size to each invaded site. Forty herbaceous species were identified in the area. There were significant differences (P < 0.05) noted in species richness, basal cover, litter cover, top hamper, plant vigour, and species diversities between invaded and uninvaded sites, with uninvaded sites recording higher values than invaded sites. Altitude, erosion and the edaphic variables pH, N, P and K, which were included as explanatory variables, also differed significantly (P<0.05) between invaded and uninvaded sites. Of the 30 D. cinerea invaded plots established for herbaceous species assessments, 26 were positively correlated with altitude, erosion, pH, P, N and K. It is imperative to find ways of managing D. cinerea in order to reduce its adverse effects on herbaceous species. RESEARCH ARTICLE Launched to accelerate biodiversity conservation A peer-reviewed open-access journalClarice Mudzengi et al. / Nature Conservation 7: 51-60 (2014) 52

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Key issues of concern regarding the environmental impacts of livestock on grazing land are their effects on soil, water quality, and biodiversity. This study was carried out to determine how grazing intensity influences soil physical and chemical properties and occurrence of herbaceous plant species in dambo wetlands. Three categories of grazing intensity were selected from communal, small scale commercial and large scale commercial land. Dambos from the large scale commercial land functioned as the control. Data analysis included ANOVA and multivariate tests from CANOCO. There were significantly negative changes to soil nutrient status in communal dambos though with a higher number of rare taxa. Sodium, phosphorous, pH and infiltration rate were significant determinants of plant species occurrence. Overgrazing is threatening the productivity, stability, and ecological functioning of dambo soils in communal Zimbabwe. These dambos also require special conservation and management priorities as they contain a large number of rare plant species.

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