Hilton G. T. Ndagurwa

Termitaria as preferred browsing patches for black rhinoceros ( Diceros bicornis ) in Chipinge Safari Area, Zimbabwe

This study tested the hypothesis that the black rhinoceros browses more on termitaria than off termitaria vegetation due to elevated soil and foliar nutrient levels on termitaria. We investigated the role of termitaria in providing nutrient-rich forage for the black rhinoceros, by comparing the preference (selection ratio) for vegetation occurring on and off termitaria, and then testing its relationship with foliar nutrient concentrations. Soil nutrients, bite intensity, tree species diversity, vegetation density, canopy cover and basal area were also surveyed on and off termitaria. We sampled 25 termite mounds together with their corresponding control plots in Chipinge Safari Area, Zimbabwe. Soil and foliar N, P, K, Ca and Na concentrations were greater on termitaria than off termitaria, with approximately twice the concentration of these nutrients. Browse preference followed the between-site differences in soil and foliar nutrient concentrations, with higher selection ratios and bite intensities for vegetation on termitaria than off termitaria. Diospyros quiloensis was the most preferred browse species whilst Combretum imberbe, Kigelia africana and Strychnos innocua were the least. In conclusion, the black rhino preferred vegetation on termitaria to that in the surrounding matrix, and utilization of vegetation can be influenced by the soil substrate on which tree species grow.

The influence of mistletoes on nitrogen cycling in a semi-arid savanna, south-west Zimbabwe

This study investigated the effects of mistletoe infection on N cycling in a semi–arid savanna, south-west Zimbabwe. We established five plots (10 × 10 m) which each included three large canopy-dominant Acacia karroo trees infected by one of three mistletoes ( Erianthemum ngamicum , Plicosepalus kalachariensis and Viscum verrucosum ) and non-infected A. karroo trees. In each plot, we measured litterfall, litter quality (N, phenolics, tannins and lignin), soil nutrient concentrations and N transformations beneath tree canopies. Soil N, P and Ca were greatest beneath trees infected by P . kalachariensis than beneath non-infected trees. Litterfall and litter N returns were 1.5, 2 and 1.4 times more beneath A. karroo trees infected by E . ngamicum , P . kalachariensis and V. verrucosum , respectively. Mineral N increased with mistletoe infection but did not exceed 20%. Soil N transformations were greater beneath trees infected by E . ngamicum (> 40%), and lower beneath trees infected by P . kalachariensis ( V . verrucosum ( A. karroo trees. Soil N transformations were negatively correlated with condensed tannins, lignin and lignin : N. We conclude that the improved N concentration can increase resource heterogeneity, which may alter the ecosystem structure and functioning in the semi-arid savanna.

Patterns of mistletoe infection in four Acacia species in a semi-arid southern African savanna

In a range of systems, studies on mistletoe distribution on the host plant have documented a number of factors that affect their occurrence and spread (Aukema & Martinez del Rio 2002a, Bowie & Ward 2004, Overton 1996, Reid et al . 1995). These patterns can be determined by host specificity, environmental conditions, host plant characteristics (Martinez del Rio et al . 1995) and the movement patterns of dispersal agents (Aukema & Martinez del Rio 2002a, 2002b). In mistletoe plants, host choice can be considerably influenced by the advantages of interacting with relatively abundant hosts (Norton & Carpenter 1998, Norton & De Lange 1999). Besides the relative abundance of host species, characteristics such as branch size, age and height can have a strong effect on mistletoe attachment resulting in size-related mistletoe infection patterns (Overton 1994). Generally positive relationships between mistletoe infection and host size have been demonstrated worldwide (Donohue 1995, Martinez del Rio et al . 1996, Norton et al . 1997, Reid & Stafford Smith 2000) and they have been interpreted in terms of the preferences by dispersing birds to perch and feed in taller trees (Aukema & Martinez del Rio 2002a) and trees accumulating infections as they age (Overton 1994). Aukema & Martinez del Rio (2002a) reported more frequent perching in taller-than-average trees by the phainopepla ( Phainopepla nitens ), which is the principal disperser of the desert mistletoe Phoradendron californicum . Thus, visits by mistletoe-seed-dispersing birds, and therefore mistletoe seeds received, tend to increase with tree height (Aukema & Martinez del Rio 2002a). Using a simple metapopulation model, Overton (1994) predicted the frequency of parasitized trees to increase with host age. Therefore, assuming that size is a good proxy for age, large trees are likely to be more infected than smaller trees. Reid & Stafford Smith (2000), using experimentally disinfected trees, found that larger trees were disproportionately re-infected with mistletoes. This size–intensity relationship may be used to describe mistletoe infection patterns. However, several previous studies have shown size–intensity relationships to be weak (Aukema & Martinez del Rio 2002a, Donohue 1995, Overton 1994, Reid & Stafford Smith 2000). This indicates that other factors may be important in determining mistletoe infection intensity, including that already parasitized hosts of a specific height are more likely to receive seeds than non-parasitized hosts of the same height or dispersers are likely to be attracted to trees for reasons other than size (Aukema & Martinez del Rio 2002a).

Effect of land use on water quality and phytoplankton community in the tropical Khami River in semi-arid southwest Zimbabwe

The water quality and phytoplankton community assemblage of the Khami River, a tropical river sub catchment in semi-arid southwest Zimbabwe impacted by agriculture and urban land use, were examined in March 2015. Conductivity, sulphates, total dissolved solids and salinity were higher at urban sampling points than at agricultural sampling points. In contrast, agricultural sampling points were more turbid, and had a greater content of nitrates than urban sampling points. The phytoplankton community was dominated by Cyanobacteria, mainly Microcystis aeruginosa, with densities of up to 20 times higher at urban than at agricultural sampling points. There was an increasing dominance of Cyanobacteria (M. aerugionosa and Merismopedia glauca) and Chlorophyta (Eudorina elegans, Spirogyra sp. and Pediastrum duplex) and a decreasing importance of Bacillariophyta along the agriculture-to-urban gradient. Given the increasing scarcity of water in southern Africa, not only do our findings confirm the importance of land use types as drivers of water quality and phytoplankton community composition and structure. However, they also show that Cyanobacteria, Chlorophyta and Bacillariophyta can be indicators of changes in water quality, factors that will prove pertinent to management for effective water quality management using phytoplankton composition as bioindicators.