Acacia Karroo Research Articles

Influence of litter source on soil splash rates and organic carbon loss in different soil horizons

Organic litter stabilizes soil particles against the raindrop splash effect. To date, limited research has critically examined the effects of litter quality on soil aggregate detachment and soil organic carbon loss by raindrop splash impact. A study was conducted to determine the effects of different litter sources on quantity of splashed sediments and soil organic carbon (SOC) loss under simulated rainstorm patterns. Soils from seven sieved (< 0.25 mm) horizons mixed with either high-quality Vachellia karroo leaf (C/N = 23.8) and/or low-quality Zea mays stover litter (C/N = 37.4) were incubated in a laboratory for 30 weeks. Splashed sediments and SOC were measured at 1, 3, 8, 14, 23 and 30 weeks of incubation for each soil at 360 mm/h simulated rainfall intensity applied as either single 8-min rainstorm (SR) or 4 × 2-min intermittent rainstorms (IR) separated by a 72-h drying period. Organic litter significantly (P < 0.05) reduced the splashed sediments up to 8 and 14 weeks under IR and SR storms, respectively, and thereafter gradually lost its stabilizing effect on soil aggregates. In order to maintain low quantities of splashed sediments, fresh litter has to be re-applied after this stage. Generally, 13% and 25% more sediments were splashed under IR than SR at 1, 3 and 30, and 8, 14 and 23 weeks after incubation, respectively. Litter quality effect on splash sediments varied across soil horizons but were the same within a soil horizon. Soil horizons with more clay than sand particles had lower quantities of sediments. The SOC loss was influenced by the initial SOC content and primary particle size distribution. Rainstorm pattern and initial SOC content were the main factors that influenced SOC loss. However, more rainstorm patterns should be investigated for these soils.

Epiphytic Lichen Diversity on Jacaranda and Acacia Trees in Pretoria (Tshwane, Republic of South Africa)

Maphangwa, K.W., Sipman, H.J.M., Tekere, M, & Zedda, L. 2018. Epiphytic lichen diversity on Jacaranda and Acacia trees in Pretoria (Tshwane, Republic of South Africa). – Herzogia 31: 949–964.

English

The study was conducted in Alice, Eastern Cape Province, South Africa. The objective of this study was to evaluate farmers’ perceptions on the impact of Vachellia karroo encroachment on livestock production and vegetation. Forty farmers (62% females and 38% males) were interviewed using semi-structured questionnaires. The results showed that goats and cattle were mainly kept for cash sales and sheep for wool production. Shortage of forage and lack of water points were the main constraints to livestock production, especially during the dry season. Cattle and sheep owners perceived that V. karroo encroachment had a negative impact on grazer production, as it reduces the grazing capacity of the veld. Goat owners viewed V. karroo as an acceptable tree to goats and its abundance favours browsers as compared to grazers. Although farmers have different views concerning the impact of V. karroo encroachment. The mean of livestock composition showed that goats (11.6±1.3) are more favoured by the veld condition compared to cattle (4.9± 1.1) and sheep (2.6±0.7). This study concludes that V. karroo had a negative impact on grazers’ production and sheep and cattle owners observed V. karroo encroachment as a form of land degradation. Pastoralists recommended that veld burning and bush clearing can be used to mitigate encroachment. Key words: Encroachment, degradation, livestock composition, Vachellia karroo.

Differing patterns of plant spinescence affect blue duiker (Bovidae: Philantomba monticola) browsing behavior and intake rates.

The ways in which spines and thorns on plants affect browsing behavior and instantaneous intake rate (IIR) have been investigated for several medium and large ungulates, with most authors concluding that spines either affect the ability to obtain a full bite, or prevent the removal of twig material. We investigated how a very small ruminant, the blue duiker (Philantomba monticola; mass 5 kg), altered its feeding strategy when confronted with intact or despined branches of three species of woody plant that differed in leaf and spine size, density, and arrangement, viz. Dichrostachys cinerea africana, Vachellia (Acacia) karroo and Ziziphus mucronata. Increasing spine length and density reduced IIR (g/min), while bite size was directly related to leaf area. Bite rate and the lag time to taking the first bite did not differ among treatments. In all treatments, blue duikers cropped leaves in preference to pruning shoots. High spine density forced duikers to crop leaves at the ends of branches where spines were softer. At low spine density and on despined treatments, leaves midway along branches were preferred. Single bites (using incisors) were used preferentially in the presence of spines, with a shift to cheek bites on despined branches. We conclude that, as found with larger browsers, spines coupled with small leaf size provide the best defense against defoliation.

Effects of litter source on the dynamics of particulate organic matter fractions and rates of macroaggregate turnover in different soil horizons

SummarySoil texture influences the transformation of soil organic matter (SOM), and depletion and reduction in the number of macroaggregates. However, the extent of changes in SOM in response to its quality and mechanisms of stabilization in different types of soil texture is unclear. We evaluated changes in SOM during a 30‐week incubation experiment using seven soils mixed with two sources of litter; Vachellia karroo (Hayne) Banfi & Galasso leaf and Zea mays L. stover. We hypothesized that changes in intraparticulate organic matter (iPOM) are influenced by litter quality • soil type • time interactions, which affect rates of turnover of macroaggregates. A completely randomized design was used in arranging soil jars in the incubator. Free light fractions and coarse and fine iPOM within macroaggregates (>250 μm) decreased exponentially from week 1 to 30 and were significantly (P < 0.05) affected by litter source • soil horizon • time interactions. Trends of changes in fine iPOM fractions were the same in macroaggregates and microaggregates (P < 0.05). The greatest changes in POM fractions occurred 8 weeks after litter incorporation. Both V. karroo leaf and Z. mays stover stabilized macroaggregates during the first 8 weeks after incubation; thereafter they lost their influence. Therefore, we needed to reapply fresh litter after this period. Changes in iPOM fractions and macroaggregate turnover were specific to a soil type, suggesting that different sources of litter have different stabilizing effects in macroaggregates. Soil macroaggregate stabilization and changes in iPOM could be used as indicators to apply more appropriate management practices for soil protection or productivity.HighlightsDoes the source of organic matter affect transformation rates of different intraparticulate organic matter in the soil? Degradation of organic matter into very fine particulate matter also increases the rate of turnover of macroaggregates. Soil type • litter source interactions greatly influenced the rate of transformation from coarse to fine intraparticulate fractions. Effects of litter quality on dynamics of POM fractions in aggregates and macroaggregate turnover were horizon specific.

Selected South African plants with tyrosinase enzyme inhibition and their effect on gene expression

Hyperpigmentation causes patches of skin to blemish and may lead to serious skin disorders. Prevention of hyperpigmentation would require suppressing the melanogenesis pathway which uses the rate limiting enzyme tyrosinase. South African plant extracts, Myrsine pillansii, Rapanea melanophloeos, Vachellia karroo, Kalanchoe thyrsiflora, Ormocarpum trichocarpum and Myrsine africana were tested for their tyrosinase inhibiting potential at both the tyrosinase activity and tyrosinase gene expression levels. The plant extracts, O. trichocarpum and V.karroo, have the most effective inhibition of 50% of the tyrosinase enzyme at concentrations of 2.95 and 6.84 μg/ml, respectively. The cytotoxicity of the plant extracts were investigated using B16-F10 mouse melanocyte cells. The tyrosinase gene expression levels were examined on the B16-F10 mouse melanocyte cells treated with the South African plant extracts, through real-time reverse transcription polymerase chain reaction (RT-qPCR). Three of the mouse melanocyte samples treated with K.thyrsiflora, M. pillansii and V.karroo showed significant down regulation of tyrosinase gene expression (p-value < 0.05) at 1.2, 3.7 and 12.7 fold, respectively. These plant extracts indicate depigmenting potential through inhibition of tyrosinase directly and at the transcriptional level and therefore, should be investigated further.

Spatial distribution ofVachellia karrooin Zimbabwean savannas (southern Africa) under a changing climate

AbstractClimate change projections in southern Africa show a drier and a warmer future climate. It is not yet clear how these changes are going to affect the suitable habitat of bush encroacher woody species in southern African savannas. Maximum Entropy niche modelling technique was used to test the extent to which climate change is likely to affect the suitable habitat ofVachellia karrooin Zimbabwe based on six Global Climate Models (GCMs) from Coupled Model Intercomparison Project Phase 5 (CMIP5) and two Representative Concentration Pathways (RCPs) for the 2070s. An overlay analysis was then performed in a Geographic Information System based on the current and future bioclimatically suitable areas for the respective GCMs and RCPs. This was done to determine the potential effect of climate change on the focal species. Results show that temperature related variables are more important in explaining the spatial distribution ofV. karroothan precipitation related variables. In addition, results indicate an overall increase in the modelled suitable habitat forV.karrooby the 2070s across the GCMs and RCPs considered in this study. Specifically, the suitable habitat ofV.Karroois projected to increase by a maximum of 57,594 km2signifying a 69% increase from the current suitable habitat (83,674 km2). The suitable areas are projected to increase in eastern, western and south eastern parts of Zimbabwe. These results imply that improved understanding of the response of woody species to a changing climate is important for managing bush encroachment in savanna ecosystems.

CO2 enrichment does not entirely ameliorate Vachellia karroo drought inhibition: A missing mechanism explaining savanna bush encroachment

There is theoretical, empirical and modeled evidence that atmospheric enrichment of carbon dioxide (CO2) is driving the conversion of open savannas to woodlands (i.e., woody thickening or bush encroachment). This study measured the impacts of available CO2 and water limitation on seedling growth and physiology to determine how these two environmental conditions may be influencing savanna seedling establishment. We hypothesized that a model savanna tree, Vachellia karroo, would experience positive growth responses to increasing CO2 and that CO2 enrichment would partially offset slowed growth and physiological inhibition imposed by drought. To test this hypothesis, we grew V. karroo in open-top chambers at the Kirstenbosch Research Center (Cape Town, South Africa). The seedlings were divided equally into four CO2 treatments: 180 ppm, 270 ppm, 400 ppm, and 800 ppm. Seedlings were grown in their CO2 treatments for 35 days before drought was initiated. The drought was initiated by removing the irrigation from half of the pots. Leaf gas-exchange, stem water potential, leaf non-structural carbohydrate concentrations, and plant morphology were measured at drought day-30 and drought day-60. The results showed significant benefits from CO2 enrichment to aboveground plant structures, including larger leaves and stems, when water was abundant (p < 0.05). CO2-related increases to photosynthetic parameters, such as instantaneous water-use efficiency, were significantly diminished by water limitation (p < 0.05). Our results present the first experimental evidence of the relationship between the two driving factors structuring the large-scale spatial patterns of savanna vegetation productivity and cover. These results suggest that atmospheric enrichment of CO2 will significantly affect aspects of plant growth and physiology, yet prolonged drought will remain an overarching determinant of savanna plant community dynamics.

Ant (Formicidae) Assemblage in South Africa'sVachellia(Acacia)karrooThorns

Ant occupancy in thorns of Vachellia (Acacia) karroo (Hayne) Banfi and Galasso was examined along the banks of the Great Fish River near Grahamstown, South Africa. Half of all thorns with visible openings contained ant nests. Colonies of Tetraponera emeryi (Forel) and a single unidentified Tapinoma species were present in over 40% of thorns with openings. Cataulacus intrudens (Smith, F.) was regularly encountered but at a much lower frequency. A single nest of Tetraponera natalensis (Smith, F.) and two Nesomyrmex stramineus (Arnold) nests were also found. The size of contiguous patches of A. karroo was not related to the percentage of thorns occupied by ants. The A. karroo ant assemblage appears to be mediated by the availability of suitable nesting thorns rather than competitive interactions.

Transient effects of nitrogen addition and rainfall suppression on Vachellia karroo growth under grass competition in a southern African savanna

It is not clear how woody species, especially nitrogen fixers will respond to the combined effect of increased N fertilisation and reduced rainfall amount in savannas in a changing environment. A f...

Tree legumes-temperate grass agroforestry system effects on inorganic soil nitrogen as ecosystem services provision for smallholder farming systems in South Africa

ABSTRACTNitrogen is an essential macro-nutrient for plant growth and is indispensable for high agricultural food productivity and quality. Shortage of good quality forage under the dry winter season and low soil fertility conditions are the major constraints in rural farming systems in the Moist Tall Grassveld of the Upper Thukela, South Africa. The effect of legumes on inorganic soil nitrogen was assessed in an agroforestry trial (Leucaena leucocephala (Lam.) De Wit, Acacia karroo Hayne, Dactylis glomerata L., Festuca arundinacea Schreb.), by soil sampling method. In the agroforestry trial, total inorganic soil nitrogen accumulation was significantly greater under intercropping than under sole crop treatments and, irrespective of the treatments, significantly more nitrate than ammonium nitrogen was measured. The study demonstrated that intercropping grasses with tree legumes could provide important ecosystem services of nitrogen supply in the soil. The results suggested that introducing legume intercrops might constitute a relevant cropping strategy to improve the soil fertility status with regard to nitrogen while at the same time providing forage in smallholder farming systems in South Africa’s Moist Tall Grassveld regions.

Mapping riparian vegetation and charactersing its groundwater dependency at the modder river government water scheme

Groundwater use by riparian vegetation transpiration commonly results in a drawdown of the water table which may significantly reduce groundwater discharge to streams and even change the status of streams from gaining to losing. Therefore, the significance of the riparian transpiration process, due to the continuously increasing demand for integrated sustainable water resources management policies, deserves great attention. It is for this reason that the present work was evoked to research the riparian groundwater dependency and consumptive groundwater use by the streamside flora. Observations of the daily groundwater multiple hydrographs, in conjunction with average daily temperature and solar radiation, indicated that the groundwater fluctuations were due to water losses from the riparian flora. The Diospyros lycioides (shrub) and Acacia karroo (tree) communities were found to be the two dominant riparian species along the subject area. However, the results indicated that only the Acacia karroo sourced their water primarily from the groundwater storage because: 1) the isotopic signature of twig xylem water was similar to that of groundwater and 2) the rooting depth was at the water table. This species was found to abstract approximately 121,100m3/month from the riparian groundwater. This is considerably a voluminous abstraction which is most likely to pose a problem of water competition; therefore, groundwater dependency of the riverine flora must be considered in the formulation of any integrated sustainable water resources management policies in the subject area and/or similar areas for the co-existence of human society and nature.

Assessing water use by Prosopis invasions and Vachellia karroo trees: Implications for groundwater recovery following alien plant removal in an arid catchment in South Africa

Prosopis spp., (or Mesquite), is a desert adapted woody weed which has invaded large parts of arid and semi-arid regions. It has a characteristic deep tap root, and forms dense impenetrable thickets along river banks, flood plains, and seasonal water courses. Several studies have quantified the water use by Prosopis, but there is limited information on how this compares with that of co-occurring groundwater dependent indigenous tree species in the arid and semi-arid tropics. Consequently the effects of removing Prosopis on groundwater, where they co-occur with indigenous trees, are not known. This study quantified the incremental water use by Prosopis invasions compared with the indigenous deep rooted Vachellia karroo (V. karroo) trees that normally replace Prosopis once it has been cleared. The study was done in an arid catchment in the Northern Cape Province of South Africa. Stem sap flow dynamics, groundwater levels, and weather data were collected hourly over 15months in the invaded catchment. Data collection continued for a further 11months after Prosopis had been cleared to monitor the recovery of the ecosystem from the invasions. There was no significant difference (P=0.116) in the sap flux density of the two species although Prosopis had a much thinner sapwood depth than V. karroo due to its ring porous wood anatomy. However, at the stand scale Prosopis transpired more than five times more water (∼544mmy−1) than V. karroo (∼91mmy−1) since there were six times more Prosopis than the indigenous species. The removal of Prosopis slowed down the rate of decline of the water table from a pre-clearing peak of ∼8.9–5.0mmd−1 after alien plant removal. Tree transpiration was accurately predicted by a simple model that used aquifer properties and hourly changes in water table depths with a RMSE of ±0.22mmd−1 before and ±0.32mmd−1 after clearing Prosopis.

Effect of polyethylene glycol 4000 supplementation on the performance of yearling male Pedi goats fed dietary mixture levels of Acacia karroo leaf meal and Setaria verticillata grass hay

Eighteen yearling male Pedi goats weighing 21.7 ± 3.1 kg were used in a 42-day trial in a 2 (Acacia karroo leaf meal levels) × 3 (levels of PEG 4000) factorial arrangement in a completely randomized design to determine PEG 4000 supplementation levels for optimal productivity of indigenous Pedi goats fed different mixture levels of A. karroo leaf meal and Setaria verticillata (L.) P.Beauv. grass hay. Each goat was supplemented with 0, 23 or 30 g of PEG 4000 per day in addition to dietary mixture of A. karroo and S. verticillata hay. Polyethylene glycol 4000 supplementation had no effect (P > 0.05) on nutrient intake of goats. However, a diet × PEG (P < 0.05) was observed for intake of all nutrients studied. Dry matter, OM, NDF and ADF intakes per goat were optimized at PEG 4000 supplementation levels of 19.62, 19.62, 19.61 and 19.53 g/goat/day, respectively, for diets containing 20% A. karroo leaf meal. Polyethylene glycol 4000 supplementation had no effect (P > 0.05) on the apparent digestibility of all nutrients. The dietary inclusion level of A. karroo leaf meal at 20% improved (P < 0.05) DM, OM, CP, NDF and ADF digestibility of goats. Crude protein digestibility was optimized at a PEG 4000 supplementation level of 15.78 g/goat/day. Dietary mixture level and PEG 4000 supplementation had no effect (P > 0.05) on final weights of Pedi goats. Similar results were observed for blood urea and glucose concentrations of yearling male Pedi goats. However, daily body weight gain was higher (P < 0.05) in goats fed 50% A. karroo leaf meal than those on 20% inclusion level. Polyethylene glycol 4000 has potential to improve the feeding value of tanninifeorus A. karroo leaf meal.

Germination of seeds from two leguminous trees (Acacia karroo and Gleditsia triacanthos) following different pre-treatments

Germination of seeds from two leguminous trees (<i>Acacia karroo</i> and <i>Gleditsia triacanthos</i>) following different pre-treatments

Acacia karroo Hayne: Ethnomedicinal uses, phytochemistry and pharmacology of an important medicinal plant in southern Africa.

Acacia karroo (A.karroo) has been used as herbal medicine by the indigenous people of southern Africa for several centuries. The potential of A.karroo as herbal medicine, its associated phytochemistry and biological activities are reviewed. The extensive literature survey revealed that A.karroo is traditionally used to treat or manage 32 and five human and animal diseases and ailments, respectively. The species is used as herbal medicine for diseases and ailments such as colds, diarrhoea, dysentery, flu, malaria, sexually transmitted infections (STIs), wounds, and also as colic and ethnoveterinary medicine. Multiple classes of phytochemicals such as flavonoids, phenols, phytosterols, proanthocyanidin, tannin, terpenes as well as several minerals have been identified from leaves and roots of A.karroo. Scientific studies on A.karroo indicate that it has a wide range of pharmacological activities which include antibacterial, antifungal, antigonococcal, antihelmintic, antilisterial, antimalarial, antimycobacterial, antioxidant, HIV-1 reverse transcriptase, anti-inflammatory and analgesic. A. karroo has a lot of potential as a possible source of pharmaceutical products for the treatment of a wide range of both human and animal diseases and ailments. Future research should focus on the mechanisms of action of the different plant parts used as herbal medicines, isolated compounds, their efficacy, toxicity and clinical relevance.

Ecosystem‐scale impacts of non‐timber forest product harvesting: effects on soil nutrients

Summary The harvesting of non‐timber forest products (NTFPs) is a global phenomenon, the sustainability of which has been studied for many species at the individual and population level. However, the broader scale impacts of NTFP harvesting have been acknowledged but rarely examined. We assessed plant size and the soil attributes undercanopy and in the open, in replicate, paired harvested and non‐harvested sites for three NTFPs differing in the extent of biomass removed, i.e. timber for firewood from a tree (Acacia karroo), fruits from a cactus (Opunita ficus‐indica) and flowering culms from a grass (Cymbopogon marginatus). Soil variables tested included pH, resistivity, P, total N, nitrate nitrogen, ammonium nitrogen, K, Na, Ca and Mg. The extent of loss of soil nutrients decreased across the three NTFPs relative to the proportion of biomass removed. Thus, significant differences in more soil variables were evident for the firewood species, least for the fruit species and intermediate for the grass species. Lower soil pH, P, C and K were evident in soils collected underneath A. karroo, while losses in cations of Na, Ca and Mg were reported in soils underneath C. marginatus, and only NO3N losses were recorded underneath O. ficus‐indica. Synthesis and applications. Our study reveals that while non‐timber forest product (NTFP) harvesting may affect soil nutrients, this is not uniform between species and is likely to be a function of the extent of biomass removed and harvesting frequency. This indicates the need for caution in generalisations about the ecosystem‐level impacts of NTFP harvesting as well as a concerted effort to better understand impacts at a greater range of scales than has been the case to date.

Evapotranspiration from mine-affected riparian sites along the Vaal River in central South Africa

Long-term gold mining within the Witwatersrand Basin Goldfields has led to the creation of over 200 tailings storage facilities (TSFs) releasing acid mine drainage. Plumes of contaminated shallow groundwater occur downslope of these TSFs. One such area lies adjacent to the Vaal River east of the town of Orkney. Natural vegetation in the riparian soils comprises a mixture of grasslands, reeds and woodlands dominated by Vachellia karroo. The Mine Woodlands Project initiated by Witwatersrand University and AngloGold Ashanti is exploring the use of engineered woodlands for hydraulic control of plumes and immobilization of contaminants to protect the wider hydrological resource. To estimate the net increase in evapotranspiration (ET) resulting from various remedial woodlands, ET from existing vegetation types requires quantification. Growing season patterns of ET were measured and modelled in riparian grassland and two V. karroo woodland sites close to the Vaal River. Two independent estimates of annual ET from these woodland sites (674 and 787 mm) were similar to that from grassland (697 mm) and much less than the 1100–1200 mm reported from some forms of engineered evergreen woodlands established in the vicinity. We conclude that the Vachellia woodlands have low potential for hydraulic control of contaminant plumes.

Population biology and ecology of Vachellia (Acacia) karroo (Hayne) Banfi & Galasso, in the Nylsvley Nature Reserve, Limpopo Province, South Africa

Population biology and ecology of Vachellia (Acacia) karroo (Hayne) Banfi & Galasso, in the Nylsvley Nature Reserve, Limpopo Province, South Africa

A Report on the In Vitro Antioxidant Properties of Vachellia karroo Leaf Extract: A Plant Widely Grazed by Goats in the Central Eastern Cape of South Africa

The polyphenolic constituents and antioxidant activity of aqueous and acetone extracts of Vachellia karroo leaves were determined in order to evaluate its efficacy in scavenging radicals such as DPPH, ferric reducing power and nitric oxide as an antioxidant model. The flavonols and flavonoid and phenolic content of the leaf extracts were also accessed using benchmark phytochemical reaction methods. Results of the phytochemical analyses revealed the presence of flavonoids and flavonol and phenolic compounds in the leaf extracts. The total phenolic content values in the aqueous and acetone leaf extracts were 7.40 and 11.09 mg tannic acid equivalent/g of extract powder, respectively. The total flavonol and flavonoid content values of the aqueous leaf extracts were 9.90 and 53.23 mg quercetin equivalent/g of extract, respectively, while those of the acetone leaf extracts were 1.18 and 5.18 mg quercetin equivalent/g of extract, respectively. At 0.2 mg/mL, the values for the scavenging activities of the acetone and aqueous extracts of the V. karroo leaves were significantly higher (p &lt; 0.05) than that of the ascorbic acid but comparable to BHT against ferric oxide radicals. The findings from the study reveal that the antioxidative potentials of V. karroo leaf extract and could serve as free radical inhibitors, possibly acting as principal antioxidants.