Shakkie Kativu

Stream fish assemblages in relation to environmental factors on a montane plateau (Nyika Plateau, Malawi)

Few studies have examined river fishes of Malawi. This study is one of the first to examine the stream fish assemblages on the Nyika Plateau in northern Malawi. Twenty four sites were sampled over three different periods in two river systems of the plateau. Eighteen species were collected and among these was Hippopotamyrus ansorgii, the first collection of this species in the Lake Malawi catchment. Three species, including a non-native trout, were common in the two systems studied. Correspondence analysis (CA) suggested gradients in species composition related to altitude and river type. Species succession, from a trout dominated upstream to a downstream dominated by indigenous species, was shown on the first CA axis. The second CA axis showed the assemblage of the plateau separated by river type. A direct gradient analysis method, canonical correspondence analysis (CCA), showed the importance of two stream position metrics (stream order and c-link), depth, water temperature and substrate type in determining species composition. According to variation partitioning in CCA, the spatial and temporal components respectively explained 46% and 3.6% variation in assemblage composition based on the all species data matrix, and 48.7% and 2.6% variation in assemblage composition based on the native species data matrix. The species collected were also discussed in relation to the morphological adaptations in their body forms to the environmental conditions of the streams studied.

Abundance and Structure of African Baobab (Adansonia digitata) across Different Soil Types in Gonarezhou National Park, Zimbabwe

This study investigated the abundance and structure of African baobab (Adansonia digitata) across soil group strata in Gonarezhou National Park, Zimbabwe. The study was based on a stratified random sampling design composed of the following soil group substrates: (i) granophyres, (ii) malvernia, and (iii) rhyolite. Belt transects of  km were randomly laid across soil group. Baobab abundance and population structure were determined from the density and size class distribution, respectively. There were significant differences in plant height and plant density across Gonarezhou soil groups. Study sites on granophyres derived soil group indicated viable abundance and recruitment of baobab population. Whereas the study highlighted a concern over the unbalanced size structure distribution of baobab population on malvernia derived soil group, our results indicated that baobabs are in danger of extirpation on malvernia derived soil group. Baobab community in Gonarezhou tends to occur more densely along environmental gradient of soil group type as influenced by the underlying geological soil substrate of granophyres. Malvernia derived soil group is likely less ideal for baobab recruitment.

Predicting the spatial distribution of hunted and non-hunted Sable antelope (Hippotragus niger niger) using remotely sensed woody cover in a Southern African savanna

From remotely sensed woody cover, we tested whether sables under hunting pressure preferred closed woodland habitats and whether those not under hunting preferred more open woodland habitats. We applied a two factorial logistic regression analysis to model the probability of occurrence of sable antelope in hunted and non-hunted areas of northwest Zimbabwe as a function of vegetation cover density (estimated by a normalized difference vegetation index (NDVI)). We validated the results by high-spatial resolution imagery derived tree canopy area. We subsequently compared the predictions from the two models in order to compare sable cover selection between hunted and non-hunted areas. Our results suggest that hunted sables are likely to select closed woodland, while non-hunted ones would prefer more open woodland habitats. We also established a significant positive relationship between NDVI and tree canopy cover, thus emphasizing the importance of remote sensing in studies that measure the impact of hunting on habitat selection of targeted species.

Comparing terrain and vegetation-based visibility for explaining sable flight behaviour in a Southern African savanna

In this study, we tested whether terrain-based visibility modelled from a remotely sensed ASTER Digital Elevation Model (DEM) explains sable flight initiation distance (FID) better than vegetation-based visibility measured in the field. We also tested whether the effect of hunting on sable FID varies with spatial scale. We first performed a linear regression analysis relating FID to standardized coefficients of both vegetation- and terrain-based visibility where the variable with the larger coefficient was the better predictor of FID. We latter performed an analysis of covariance (ANCOVA) comparing the slopes relating FID to both measures of visibility, first at the large scale and later at the small scale within the hunting area. Our results suggest that remotely sensed terrain-based visibility predicts the FID of sable better than vegetation-based visibility. We also found that the effect of hunting on sable FID varies with spatial scale.

A study on microsporogenesis and ovule morphology in tropical African Anthericaceae and Asphodelaceae

A study on tropical African species of Anthericaceae and Asphodelaceae showed that microsporogenesis is successive in Anthericaceae and simultaneous in Asphodelaceae. Both families have anatropous ovules and frequently have nectaries and raphids. Type of microsporogenesis appears to be an important taxonomic character at the family level.

Varying Land-Use Has an Influence on Wattled and Grey Crowned Cranes’ Abundance and Distribution in Driefontein Grasslands Important Bird Area, Zimbabwe

Three species of cranes are distributed widely throughout southern Africa, but little is known about how they respond to the changes in land-use that have occurred in this region. This study assessed habitat preference of the two crane species across land-use categories of the self contained small scale commercial farms of 30 to 40 ha per household (A1), large scale commercial agriculture farms of > 50 ha per household (A2) and Old Resettlement, farms of < 5 ha per household with communal grazing land in Driefontein Grasslands Important Bird Area (IBA), Zimbabwe. The study further explored how selected explanatory (environmental) habitat variables influence crane species abundance. Crane bird counts and data on influencing environmental variables were collected between June and August 2012. Our results show that varying land-use categories had an influence on the abundance and distribution of the Wattled Crane (Bugeranus carunculatus) and the Grey Crowned Crane (Belearica regulorum) across Driefontein Grasslands IBA. The Wattled Crane was widely distributed in the relatively undisturbed A2 farms while the Grey Crowned Crane was associated with the more disturbed land of A1 farms, Old Resettlement and its communal grazing land. Cyperus esculentus and percent (%) bare ground were strong environmental variables best explaining the observed patterns in Wattled Crane abundance across land-use categories. The pattern in Grey Crowned Crane abundance was best explained by soil penetrability, moisture and grass height variables. A holistic sustainable land-use management that takes into account conservation of essential habitats in Driefontein Grasslands IBA is desirable for crane populations and other wetland dependent species that include water birds.

Pattern of Land-Use and Land Cover Changes in Driefontein Grassland Important Bird Area, Zimbabwe

We assessed land cover and land use change in Driefontein Grasslands Important Bird Area (Driefontein IBA), Zimbabwe, after the land reforms that took place in 2000, using remotely sensed satellite land cover images of 1995, 2000, 2005 and 2010. A drive transect was done for ground truthing. Data were analysed spatially in a Geographical Information System environment. Changes in land cover and land use proportions were recorded from 1995 to 2010 throughout the Driefontein IBA. The land cover classes of grassland and wetland showed a decrease, whereas land area under cultivation increased during 1995–2010. However, the woodland area marginally remained constant over the same time. We concluded that changes in land cover in the study area were largely driven by land use change, i.e., increase in cultivation, following the resettlement of people within the Driefontein IBA. It is likely that with increasing human population the natural habitat of the study area will be degraded further, negatively impacting key sensitive habitats such as wetlands, bird species, and other biodiversity. Threats to birds and wetlands habitats are also threats to human livelihoods because people in this semi-arid area depend on wetland ecosystem services for their survival. The study recommends continuous monitoring of Driefontein IBA for conservation of birds and their habitats.

Diversity and host associations of ectomycorrhizae fungi in fallow lands of the mid-Zambezi valley area, Zimbabwe

Fallowing creates land mosaics characterised by vegetation communities at different stages of succession. Such mosaics are expected to harbour mycorrhizal associations that reflect host species composition and diversity. We investigated the diversity of ectomycorrhizal fungi and their host associations across a fallow crono-sequence of 1–14 years in the mid-Zambezi valley area, Zimbabwe. Five ectomycorrhizal fungi species: Lactarius gymnocarpus, Lactarius sp., Boletus sp., Thelephora terrestris and Amphinema byssoides were recorded from 13 tree species from six families: Combretaceae, Ebenaceae, Fabaceae, Simaroubaceae, Rhamnaceae and Tiliaceae. The results indicated low host specificity among the observed ectomycorrhizal fungi. A Spearman Rank correlation test showed no significant correlation (p > 0.05) between fallow age and ectomycorrhizal status. The Raup–Crick similarity cluster indicated an interaction between fallow age and ectomycorrhizal fungi status on tree species. Our results support reports on low host specificity for ectomycorrhizal fungi among tropical African plant communities.

Dynamics of fallow secondary succession pathways and prospects of ecosystem recovery in semi-arid agricultural landscapes

ABSTRACT This study investigates the dynamics of secondary succession pathways and analyses the prospects of ecosystem recovery on two soil types in the semi-arid mid-Zambezi valley, northern Zimbabwe. Thirty-five fallow plots of different ages, ranging from one to twelve years since abandonment and twenty 0.09 ha plots of mature woodland were sampled. The results showed observable changes in vegetation features along the chronosequences of recovering fallow plots. There were significant (p<0.05) relationships between fallow age and tree density and tree diameter at breast height (DBH) with an observable decrease in tree diversity with increasing fallow age. The dominant species within the recovering fallow vegetation were different from the defining species within the natural woodlands. Acacia tortilis subsp. spirocarpa exclusively dominated the vegetation in older fallows and it was less clear whether typical woodland species would regain dominance. Therefore, management efforts may have to focus on initiatives aimed at conserving existing woodlands, which will be vital for the maintenance of defining species.

Soil based assessment of the invasive species Vernonanthura phosphorica (Vell.) H. Rob. (Asteraceae) in Burma Valley, Zimbabwe

Sites occupied by Vernonanthura phosphorica in Burma Valley, Zimbabwe tend to be species poor, with the invasive species dominating the flora. An investigation was carried out to establish soil conditions under which V. phosphorica, an invasive alien shrub, thrives. Five randomly selected sites under V. phosphorica invasion were compared to five adjacent sites unoccupied by the species. Plots measuring 20  m × 20  m were randomly placed within each site. Five 1  m × 1  m quadrats were systematically laid at the four corners and centre of each plot and sampled for soil nitrogen, phosphorus, carbon, pH and temperature. An independent t-test was used for the analysis of these variables. Results showed that the invaded sites had significantly higher soil nitrogen and phosphorus content and temperatures than sites unoccupied by the invasive species. Soil pH and carbon were significantly lower on invaded sites. The observed soil physical and chemical differences between each set of sites provided an insight into conditions under which the invasive species thrives. It was, therefore, concluded that the invasive V. phosphorica thrives under high soil temperature, nitrogen and phosphorus content and low soil pH and carbon.