Influence of fire frequency on Colophospermum mopane and Combretum apiculatum woodland structure and composition in northern Gonarezhou National Park, Zimbabwe

We investigated the long-term effects of fire frequency on Colophospermum mopane and Combretum apiculatum woodland structure and composition in northern Gonarezhou National Park (GNP), Zimbabwe. Fire frequency was categorised as high (every 1–2 years), medium (every 3–4 years) and low (every 5–6 years). The following variables were measured or recorded: plant height, species name, canopy depth and diameter, basal circumference, number of stems per plant, plant status (dead or alive) and number of woody plants in a plot. There was a positive correlation (r = 0.55, P = 0.0007) between annual area burnt (total from January to December) and annual rainfall (average over two rain stations per rain year, July to June) between 1972 and 2005. A total of 64 woody species were recorded from C. mopane and C. apiculatum woodlands. Mean plant height increased from 4.5 to 8.2 meters in C. mopane woodland and from 4.5 to 5.1 meters in C. apiculatum woodland in areas subjected to high and low fire frequencies. In C. mopane woodland, low fire frequency was characterised by a significantly low density of woody plants (P 0.05). Our results suggest that C. mopane and C. apiculatum woodlands are in a state of structural transformation. Fire frequency effects, however, appear to be woodland specific. Fire management strategies in GNP should take into consideration annual rainfall and the different vegetation type

Ecosystem recovery analysis of mine tailings at Mhangura copper mine through normalised difference vegetation index

Remote sensing techniques are increasingly being employed in monitoring environmental change. Vegetation indices such as normalised difference vegetation index (NDVI), are useful in estimating primary production, an important component of ecosystem function. The success of rehabilitation on mine tailings may be indirectly assessed through NDVI changes. Mine tailings at Mhangura copper mine, Zimbabwe, have not been monitored since their rehabilitation following the mine closure in 2000. The present study indirectly assesses primary productivity over the tailings dams as a way of establishing the extent of ecosystem recovery. NDVI images were obtained from the United States geological survey (USGS), global visualisation viewer (GloVis) website. These were processed using the Integrated Land and Water Information System (ILWIS) Version 3.3 GIS software. Two-way ANOVA showed significant differences in NDVI between the sites (p < 0.05). Actual NDVI trends over the years could not be established. NDVI values over the dams were also significantly different from those in adjacent natural Acacia woodland. These observations were supported by principal components and hierarchical cluster analyses. The NDVI analysis thus showed a good establishment of grass on the dams with poor tree cover when compared with the Acacia woodland. This suggests a positive movement towards recovery. However, factors preventing tree establishment need to be investigated.Keywords: Ecosystem development, normalised difference vegetation index (NDVI), remote sensing, tailings rehabilitation

Impact of African elephants on Baikiaea plurijuga woodland around natural and artificial watering points in northern Hwange National Park, Zimbabwe

The extent of African elephant (Loxodonta africana) induced damage on shrub and mature Baikiaea plurijuga trees was investigated around artificial and natural watering points in northern Hwange National Park, Zimbabwe. Damage was assessed in three zones of elephant occupancy during the dry season i.e. high elephant occupancy zone (= 1 km from water points), moderate elephant occupancy zone (> 1–2 km from water points) and low elephant occupancy zone (> 2 km from water points). A total of 48 plots along baseline transects were sampled among four artificial watering points and four natural watering points at increasing distance from the watering points. Damage to recruits, mature B. plurijuga and overall woody vegetation decreased with distance from artificial watering points. In addition, damage to mature B. plurijuga and overall woody vegetation decreased with distance from natural watering points, whereas damage to recruits did not change with distance from water points. Our results show that artificial watering points are associated with higher damage to B. plurijuga recruits and overall woody vegetation within = 1 km radius from water points compared to natural watering points. Other changes associated with increasing distance from artificial watering points were increase in canopy cover and decrease in woody species diversity. In the natural watering points, we recorded an increase in canopy cover, mean basal area of B. plurijuga shrubs and height B. plurijuga shrubs, and a decrease in species diversity with distance from watering points. Overall, woody species diversity was higher around natural watering points than around artificial watering points. Our findings suggest that browsing by large herbivores near watering points leads to the degradation of vegetation

Impact of African elephants on baobab (Adansonia digitata L.) population structure in northern Gonarezhou National Park, Zimbabwe

The impact of African elephant (Loxodonta africana) on population structure of baobab trees (Adansonia digitata L.) was assessed in northern Gonarezhou National Park (GNP), southeast Zimbabwe. Baobabs were sampled in March 2008 and September 2012 using 11 randomly laid belt transects of variable length within 1 km of the eastern and western sections of the Runde River and also away (> 1 km) from the water sources. A total of 223 baobabs, 130 near permanent water sources and 93 away from permanent water sources, were sampled. Baobab density did not significantly differ across the two study sites. Furthermore, there were no significant differences in girth at breast height between the two study sites. Results of the present study suggest that elephants target large baobabs (girth = 5 m). In contrast, significant difference in baobab damage was recorded between the two sites. A single dead baobab tree was encountered at a site away from water sources. A larger proportion of elephant damaged baobabs was located closer to permanent water sources. However, baobab recruitment and regeneration was higher in areas close to permanent water sources than in distant areas. Management should come up with strategies to monitor vegetation changes in order to avoid loss of baobabs and other tree species

Impact of African elephants on Baikiaea plurijuga woodland around natural and artificial watering points in northern Hwange National Park, Zimbabwe

The extent of African elephant (Loxodonta africana) induced damage on shrub and mature Baikiaea plurijuga trees was investigated around artificial and natural watering points in northern Hwange National Park, Zimbabwe. Damage was assessed in three zones of elephant occupancy during the dry season i.e. high elephant occupancy zone (= 1 km from water points), moderate elephant occupancy zone (> 1–2 km from water points) and low elephant occupancy zone (> 2 km from water points). A total of 48 plots along baseline transects were sampled among four artificial watering points and four natural watering points at increasing distance from the watering points. Damage to recruits, mature B. plurijuga and overall woody vegetation decreased with distance from artificial watering points. In addition, damage to mature B. plurijuga and overall woody vegetation decreased with distance from natural watering points, whereas damage to recruits did not change with distance from water points. Our results show that artificial watering points are associated with higher damage to B. plurijuga recruits and overall woody vegetation within = 1 km radius from water points compared to natural watering points. Other changes associated with increasing distance from artificial watering points were increase in canopy cover and decrease in woody species diversity. In the natural watering points, we recorded an increase in canopy cover, mean basal area of B. plurijuga shrubs and height B. plurijuga shrubs, and a decrease in species diversity with distance from watering points. Overall, woody species diversity was higher around natural watering points than around artificial watering points. Our findings suggest that browsing by large herbivores near watering points leads to the degradation of vegetation

Effects of Dichrostachys cinerea (L.) Wight & Arn (Fabaceae) on herbaceous species in a semi-arid rangeland in Zimbabwe

Anthropogenic alteration of an environment and other disturbance regimes may enable the expansion of some native species into new geographical areas, a phenomenon observed with Dichrostachys cinerea. Five D. cinerea invaded sites, each approximately one hectare in size were assessed for the effects of D. cinerea on native herbaceous species diversity, richness, basal cover, litter cover, top hamper and plant vigour. The same attributes were studied in five uninvaded sites adjacent to, and equal in size to each invaded site. Forty herbaceous species were identified in the area. There were significant differences (P <0.05) noted in species richness, basal cover, litter cover, top hamper, plant vigour, and species diversities between invaded and uninvaded sites, with uninvaded sites recording higher values than invaded sites. Altitude, erosion and the edaphic variables pH, N, P and K, which were included as explanatory variables, also differed significantly (

Chlorophytum delicatulum (Asparagaceae), a newly described species from Zambia.

Osborne, Vollesen &amp; Bjorå from Zambia is described, illustrated and placed within the context of recent taxonomic and phylogenetic work on in Africa. This delicate herb has leaf bases furnished with conspicuous dark red setae resembling eyelashes. Its phylogenetic position, ecology, phytogeography and conservation status are discussed. is assessed as being of Least Concern using the categories and criteria of the IUCN Red List

A first assessment of megaherbivore subsidies in artificial waterholes in Hwange National Park, Zimbabwe

The transfer of terrestrial organic matter by terrestrial wild and domestic animals when they urinate and defecate directly in Savanna Rivers has already been studied. However, the eulittoral zone around waterholes receives organic matter during the dry season, which is diluted in the ecosystem when the waterholes returns to its wet season level. In our study, we evaluated this pathway of subsidies in Hwange National Park, Zimbabwe, by estimating dung density in the eulittoral zone at the peak of the dry season. We also collected dung from different herbivore species during the dry and wet seasons to measure nutrient content and estimate nitrogen and phosphorus leaching rates. Our results show a decrease in carbon:phosphorus and nitrogen:phosphorus ratios in the dry season compared to the wet season. During the dry season, the deposition of total carbon, nitrogen, and phosphorus, mostly due to elephants, is estimated to be 8.65, 0.25, and 0.06g/m(2)/day, respectively, while the leaching rates of dissolved inorganic nitrogen and phosphorus are 1.52mg and 6.59mgm(2)/day, respectively. No specific coloured dissolved organic matter signature for dung was identified. We discuss the temporal dynamics of the subsidies as a distinctive feature of the system