Peter F. Scogings

Differential phenolic profiles in six African savanna woody species in relation to antiherbivore defense

Low molecular weight phenolics are suggested to have a role in mediating diet selection in mammalian herbivores. However, very little is known about low molecular weight phenolic profiles of African savanna woody species. We determined low molecular weight phenolic profiles of six woody species with different life history, morphological and functional traits. We investigated interspecific phytochemical variation between species and found that: (1) related Acacia species were chemically dissimilar; (2) similarity percentage analysis revealed that Acacia grandicornuta was most dissimilar from other species and that the evergreen and unpalatable Euclea divinorum had a qualitatively similar chemical profile to the deciduous and palatable Acacia exuvialis and Combretum apiculatum; (3) C. apiculatum had the highest chemical diversity; (4) relative to spineless plants, spinescent plants contained significantly less HPLC phenolics and condensed tannins; and (5) the major quantitative difference between the evergreen and unpalatable E. divinorum and other species was its high myricitrin concentration.

Do mammalian herbivores influence invertebrate communities via changes in the vegetation? Results from a preliminary survey in Kruger National Park, South Africa.

We investigated the indirect influence of mammalian herbivores on invertebrates, by utilising long-term mammalian herbivore exclosures in Kruger National Park. The exclosures span three distinct habitat types (crest, footslope and riparian) on a catena. By performing invertebrate collections in the exclosures and in a control area we were able to assess the indirect effect of mammalian herbivory on the invertebrate community and if this influence varied across habitat types. Our results indicate that large mammalian herbivores (notably elephants) had significant negative effects on total invertebrate abundance, while medium-sized mammalian herbivores affected the abundance and richness of beetles and grasshoppers negatively. Habitat type affected the invertebrates; spider abundance and richness peaked on the footslope, while beetles were the most abundant and taxon-rich in the riparian zone. Hence, our results suggest that indirect effects of mammalian herbivores on the invertebrate community may be significant, and in most cases negative, but also that the effects of mammalian herbivores vary across invertebrate groups. Thus, to better understand the broad-scale implications of changed mammalian herbivore pressures for the functioning of savanna systems, it may be important to take effects on invertebrate communities into account.

Does large herbivore removal affect secondary metabolites, nutrients and shoot length in woody species in semi-arid savannas?

This is the postprint version of the article published in Journal of Arid Environment. The published article can be located here: http://www.sciencedirect.com/science/article/pii/S0140196312002364

Effects of season, browse species and polyethylene glycol addition on gas production kinetics of forages in the subhumid subtropical savannah, South Africa †

BACKGROUND This study was conducted to investigate the effects of season, species and polyethylene glycol addition on gas production (GP) and GP kinetic parameters by in vitro incubation (72 h) of five plant species from the subhumid subtropical savannah, South Africa. Plant species used were Acacia natalitia, Acacia nilotica, Dichrostachys cinerea, Scutia myrtina and Chromolaena odorata, leaves of which were harvested during the dry (June/July), early wet (November/December) and late wet (February/March) seasons. An automated in vitro gas production technique was used in two experiments carried out with nine replicates. The first experiment was to test the effect of season and species, while the second experiment tested the effect of tannins using polyethylene glycol 4000 (PEG). The PEG treatment was applied to samples in the early wet and late wet seasons. RESULTS There were wide variations among seasons and species in crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and condensed tannin (CT). Season and species affected the maximum GP and GP kinetic parameters. During the three seasons, C. odorata had the highest CP (186-226 g kg(-1) dry matter (DM)) and GP (87-104 mL g(-1) DM) and S. myrtina had the lowest CP (105-129 g kg(-1) DM), while A. nilotica, A. natalitia, D. cinerea and S. myrtina had similar and low GP (23-50 mL g(-1) DM). The maximum GP, its degradation rate and GP from the soluble fraction were positively correlated with CP both without and with PEG. With PEG, GP from the soluble fraction was negatively correlated with NDF, ADL and CT; without PEG, it was negatively correlated with CT. CONCLUSION Both season and species affected the GP parameters. The addition of PEG emphasises that the inhibitory effect of tannins on rumen microbes was greater for all but C. odorata, confirming that these browse species can be used as feed supplements.

Season and plant species influence foraging efficiency of Nguni goats in pens

This study investigated the seasonal and plant species patterns of short-term intake rate (STIR) by Nguni goats fed six common browse species in subhumid subtropical savannas. Six 2-year-old castrated Nguni goats weighing an average of 26 kg each were penned individually and maintained on a basal diet of ram, lamb and ewe pellets and grass hay. The STIR was influenced by season, with the highest mean STIR recorded during the dry season (mean ± SEM: 0.18 ± 0.012 g DM s−1) and least during the late wet season (0.15 ± 0.009 g DM s−1). Broadleaf species had higher STIR than fine-leaf species (0.18 ± 0.052 g DM s−1 vs 0.14 ± 0.055 g DM s−1). Species that produce new leaves on new long shoots were consumed at higher rates than those that produce new leaves on short shoots (0.19 ± 0.054 g DM s−1 vs 0.15 ± 0.056 g DM s−1). STIR showed no clear patterns in relation to leaf chemistry. These results can be used to improve estimates of intake rates from free-foraging animals using direct observation methods based on time spent at a feeding station depending on the plant species and the season in which it is consumed.

Seasonal variations in diet selection of Nguni goats: effects of physical and chemical traits of browse

Goats select some browse species more than others, given options. Seasonal trends of diet selection of Nguni goats indexed by intake were investigated in cafeteria-style experiments. The relationships between diet selection and plant chemical/physical traits of Vachellia nilotica, Vachellia robusta, Dichrostachys cinerea, Euclea crispa, Rhus lancea and Ziziphus mucronata, representing abundant species were studied in the dry and rainy seasons. Seasonal changes in browses affected diet selection. Selection of long shoot species, which were concomitantly broad-leafed, was higher than species with short shoots. Selection was higher for spineless than spinescent species. Diet selection correlated positively with increased leaf mass. In the rainy season, cellulose positively correlated with intake, number of bites and browsing time, whereas in the dry season, cellulose correlated with bite size. Diet selection tended to be driven more by shoot morphology and leaf mass than by either spinescence or plant chemistry. Plant chemical influence on diet selection was diverse in both seasons and showed no definite trend, whereas spinescence had no significant effect on short-term intake. The results represent important input to goat production and range forage species management.

Diet selection of goats depends on season: roles of plant physical and chemical traits

This paper reports on diet selection of goats offered six browse species (i.e. Acacia natalitia [Vachellia natalitia], Acacia nilotica [Vachellia nilotica], Dichrostachys cinerea, Grewia occidentalis, Gymnosporia maranguensis and Scutia myrtina) commonly found in moist Zululand thornveld. The hypotheses tested were: (1) plant species and season affect diet selection, (2) physical traits such as leaf phenology, spinescence, shoot morphology and leaf size affect selection, and (3) selection is related to tannins, fibre and protein in ways that indicate nutrient maximisation. Six 2-year-old castrated indigenous goats weighing an average of 26 kg each were individually penned and maintained on a basal diet of pellets and grass hay. Six branches were offered simultaneously to individual goats and intake per branch recorded and used as an index for diet selection. Diet selection was significantly influenced by interactions between plant species and season. Scutia myrtina and Grewia occidentalis were consistently the most preferred species, whereas Gynmosporia maranguensis and Acacia nilotica were least preferred throughout the seasons. Goats preferred broad-leaf and long-shoot species over fine-leaf and short-shoot species across all seasons. These results suggest that short-term diet selection in subhumid areas is not as strongly influenced by leaf phenology and plant chemistry as in semi-arid savannas.

Forage–cattle relationships in a communally managed semi-arid savanna in northern Zululand, South Africa

Development of extensive livestock production in KwaZulu-Natal is constrained by seasonal variability of rangeland production and low forage nutritional quality. A three-year study was implemented to determine the seasonal variation in herbaceous biomass and chemical composition of veld, animal weight, body condition and blood metabolites in a communal area where farmers wished to commercialise. The period of study was not characterised by unusual climatic conditions. Herbaceous biomass increased in wet months and decreased in dry months. Crude protein concentration was higher in wet seasons than dry seasons. Neutral detergent fibre was generally high. Calves gained 0.53–0.63 kg d−1 during the wet season and took 15 months to reach weaning weight. The mean weights and body condition scores of cows and bulls increased during wet seasons and decreased during dry seasons. Blood urea nitrogen was low in the dry season while creatinine concentrations increased in the dry season and dropped in the wet season. The results indicated that the quantity and quality of forage were insufficient for the development of commercial beef production. Further research is needed to develop and test strategies for improving the availability of nutrients in situations where communal farmers wish to develop livestock production.

Calibration of a hand-held instrument for measuring condensed tannin concentration based on UV- and red-excited fluorescence

Condensed tannins are ecologically important compounds in plants for several reasons, e.g. as herbivore deterrents or protecting photosynthetic tissues against ultraviolet radiation. The hand-held Dualex Series 4 instrument was originally developed for indirect determination of flavonol concentrations in crops. Flavonols are low-molecular-weight phenolics from which condensed tannins are synthesised. Therefore, it was expected that the Dualexs ‘flavonol index’ (range 0.00–3.00) could be used to predict condensed tannin concentrations, providing a rapid, cost-effective, non-destructive method to sample more species and more plants per treatment than destructive methods used for wet-chemistry tannin assays. Thirteen broad-leaved woody species were sampled at the Nkuhlu and Letaba exclosures in Kruger National Park during December 2011. Four plants were sampled per species by collecting 100 leaves per plant, measuring the flavonol index of each leaf and pooling them in classes of 0.10 flavonol units. Condensed tannin concentrations were determined according to the acid-butanol assay with Sorghum tannin as standard. Regression models (condensed tannin = a*flavonol index – b) were significant for only four species: Acacia nigrescens (Senegalia nigrescens), Euclea divinorum, Spirostachys africana and Combretum zeyheri. Other than high variation in chemistry among plants, poor calibration results were likely caused by high chemical variation within leaves.

Impacts of cattle on ecological restoration of coastal forests in KwaZulu-Natal, South Africa

Livestock from communities bordered by dune mining, urban areas and commercial forestry in northern KwaZulu-Natal spend substantial time foraging in the coastal forest that the mining company is obliged to restore. A survey of livestock owners and an experimental study of impacts of cattle on restoration processes were conducted to develop better knowledge of the perceptions of livestock owners neighbouring the mine, and the impacts of their cattle on rehabilitating coastal dune forest. Shortages of grazing and livestock diseases were perceived to be the major constraints on livestock operations. Mitigation included grazing cattle in the rehabilitating forest and treating livestock diseases with available medicinal plant species. An exclosure experiment in one of the older stands undergoing restoration showed that cattle grazing reduced grass biomass and Acacia kosiensis seedling recruitment. A study of seeds collected from cattle dung showed that Psidium guajava, an important invasive alien woody species, was dispersed by cattle into the rehabilitating forest, but passage through cattle did not enhance germination of the invasive species. The study concluded that: (1) the proximity of livestock owners to large-scale commercial land uses influenced their perceptions and their resources, and (2) grazing and trampling by cattle in the rehabilitating dune forest may hinder the ecological restoration process.