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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 ofVachellia nilotica,Vachellia robusta,Dichrostachys cinerea,Euclea crispa,Rhus lanceaandZiziphus 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. [ABSTRACT FROM PUBLISHER]

Impacts of large herbivores (>5 kg) on woody plants in African savannas are potentially most severe among plants shorter than 1.6 m. It is well established that severe browsing leads to longer shoots, yet prevents saplings from recruiting into adult size-classes in African savannas. Increased shoot length, indicating faster shoot growth, is often associated with reduced concentrations of tannins and increased nutrient concentrations, suggesting carbon limitation. We hypothesized that, on average, large herbivores suppress stem height or circumference, but increase shoot length. We also hypothesized that if there were concomitant positive effects on nutrients, or negative effects on tannin concentrations, they would be greatest early in the wet season. We sampled saplings of four deciduous woody species ( Acacia grandicornuta, Dichrostachys cinerea, Combretum apiculatum and Grewia flavescens) at different stages of the wet season in a large-scale, long-term herbivore exclusion experiment in Kruger National Park, South Africa. Plant height, shoot length and stem circumference were generally not adversely affected by large herbivores, suggesting C limitation is rarely present among deciduous saplings in semi-arid African savannas, allowing them to tolerate browsing. Time since first rainfall emerged as a predominant factor consistently affecting nutrient and tannin concentrations, rather than large herbivores. Nitrogen and phosphorus generally decreased (by 20-50%), while condensed tannin concentration increased (150-350%) during the wet season, except for one species. We postulate that A. grandicornuta is less prone than other species to accumulating tannins during the wet season because of high investment of C in spines. Although nutrient and tannin concentrations were generally not affected by large herbivores, species-specific responses were evident very early in the wet season, which is when herbivore populations are most likely to be affected by differential forage quality among plants. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Nkuhlu large-scale long-term exclusion experiment in Kruger National Park was designed to study the long-term effects of large herbivores on vegetation. One treatment excludes elephants, another excludes all herbivores larger than hares and another one comprises an open, control area. Vegetation monitoring was implemented in 2002 when a baseline survey was conducted prior to exclusion. Monitoring was repeated 5 years after exclusion. Data from the surveys were analysed to establish how structure and composition of woody vegetation had changed 5 years after herbivore exclusion. The analysis showed that neither plant assemblage nor mean vegetation height had changed significantly since exclusion. However, both species richness and density of woody plants increased 5 years after exclusion of all large herbivores, but not after the exclusion of elephants alone. One already common species, Dichrostachys cinerea, became more common after excluding all large herbivores compared with either no exclusion or elephant exclusion, possibly leading to competitive suppression of other species. Species other than D. cinerea tended to either increase or decrease in density, but the changes were insufficient to induce significant shifts in the overall assemblage of woody plants. The results indicate that after 5 years of exclusion, the combined assemblage of large herbivores, and not elephants alone, could induce changes in species richness and abundances of woody plants, but the effect was so far insufficient to induce measureable shifts in the assemblages of woody plants. It is possible that assemblages will change with time and increasing elephant numbers may amplify future changes. [ABSTRACT FROM AUTHOR]

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Diet selection of black rhinoceros and forage quality factors affecting diet selection were investigated in the Great Fish River Reserve. Plant species, number of bite marks, heights and diameters of bites, and diameter of the largest bite were recorded. Five woody species were sampled to quantify forage quality factors that could influence diet selection. Twigs 2, 6, 10 and 14 mm in diameter were collected from each species for determining the dry mass (DM), crude protein (CP) and neutral detergent fibre (NDF) of the leaves and wood of browseable material as well as leaf:stem ratio (LSR). Azima tetracantha and Plumbago auriculata were the most preferred woody plants in winter and summer. Euphorbia bothae was the most preferred succulent species in summer while in winter it was Jatropha capensis. Most browsing occurred below 1 m and most browsed twigs were <6 mm in diameter. Twig bites were larger during summer than winter. Forage quality factors varied across the plant species. Plant preference was significantly related to CP and LSR. Relationships between plant preference and CP were positive while the relationships between plant preference and LSR were negative. Within forage quality factors measured CP was the major factor affecting diet selection of woody plants. [ABSTRACT FROM AUTHOR]