Rosemary Shikangalah

Fire is a key ecological driver in savanna systems, influencing soil biogeochemical processes by releasing nutrients but also causing potential losses through volatilization and leaching. In this study, we investigated how fire seasonality and soil depth influence both Mehlich-3 extractable nutrients and total elemental concentrations. This study was conducted in a long-term fire experiment consisting of 20 plots subjected to seasonal burning treatments (dry season, late dry season, late wet season, and an unburned control). Soil samples were collected from two different depth horizons (0–15 cm and 15–30 cm) and analyzed for nutrient concentrations. We used two-way PERMANOVA, Scheirer–Ray–Hare tests, and non-metric multidimensional scaling (NMDS) to assess treatment effects and interactions. Results showed that fire seasonality did not significantly affect Mehlich-3 extractable nutrients; in contrast, soil depth strongly structured nutrient profiles, with higher concentrations in the upper soil layer, while total elemental concentrations were consistently enriched in the deeper soil horizon. Fire seasonality influenced total elemental nutrient pools, with late dry season burns enhancing potassium and other cations, likely due to combustion of accumulated dry biomass and subsequent ash deposition. Depth effects were particularly pronounced for TN and OC, which were elevated in deeper layers due to the presence of mineral-associated organic matter OM. Our findings highlight that vertical stratification is the dominant control of nutrient distribution, while fire seasonality modulates specific nutrient dynamics. These results underscore the need to incorporate soil profile depth and fire timing when evaluating post-fire soil fertility and ecosystem resilience in savanna landscapes.

Southern African savanna rangelands are facing a widespread degradation pattern called bush encroachment. This is associated with implications for various aspects of the water cycle and in particular canopy transpiration. At the individual-tree scale, it is estimated by scaling sap-flux density by sapwood area. However, the direct measurement of sapwood area is impracticable at landscape scale and general allometric equations of the West-Brown-Enquist (WBE) model relating sapwood area to primary size measures seem to fail for some species and climates. Therefore, we conducted intensive field measurements to establish species-specific allometric relationships between sapwood area and sizes (stem diameter, crown area) in six dominant shrub species involved in bush encroachment in Namibia ( Colophospermum mopane, Senegalia mellifera, Vachellia reficiens, Dichrostachys cinerea, Vachellia nebrownii, Catophractes alexandri ). We found strong allometric relationships between sapwood area and stem diameter as well as between sapwood area and crown area for all six species. These relations are largely in line with the WBE theory but still provide estimates that are more accurate. Only in D. cinerea , the sapwood area was significantly smaller than predicted by the WBE theory, which might be caused by a larger need for stabilizing heartwood. Our results are useful to estimate water loss via transpiration at a large scale using remote sensing techniques and can promote our understanding of the ecohydrological conditions that drive species specific bush encroachment in savannas. This is particularly important in the light of climate change, which is considered to have major implications on ecohydrological processes in savannas.

This study determined the impact of Tebuthiuron application on plant biodiversity over a three-year period at Neudamm farm. A total of 40 (1m²) quadrats were randomly nested in three 250 m² belt transects per each treatment to record the herbaceous plant density, species composition, dry matter and ground cover. Woody plant density, heights and canopy diameters were measured in each 250 m² belt transects. A General Linear Model (GLM) procedure of SAS (2007) was used for analyses. The herbaceous biomass production was significantly higher (P < 0.05) in chemically treated site of 2015 (975 Kg DM ha^-1) and least in the other two sites. The chemically treated site of 2016 had greater (P < 0.05) ground cover percentage than the other treatment sites. The canopy cover and woody plant densities in all woody height categories were higher (P < 0.05) in the control and chemically treated site of 2017, than the other two sites. The study concluded that the Tebuthiuron had impacted on the plant biodiversity of treated rangelands by improving the herbaceous plant species, biomass yields and reduced bush density. The study recommends that aftercare practices and application of arboricides be carried out routinely to allow herbaceous plants recovery. Keywords: Bush encroachment, arboricides, plant density, biomass production, canopy

This study investigates Himba pastoralists’ perceptions of risks to their livelihoods. Using a semi structured questionnaire, 20 pastoralists from a Himba community were interviewed. The results show that there are multiple perceived risks that are seemingly threatening their livelihoods. Most of the perceived risks are associated with natural resources; primarily the limited sources of water and the lack of adequate pastures. These two are the most important factors to a semi-nomadic lifestyle; hence they pose the greatest threat to their livelihoods. Pressures from both wildlife and the increase in human population have also been recognized as risks to the community. While these perceptions of risks appear to have spurred the community into employing certain management strategies, this has not changed their semi-nomadic way of living as pastoralists. The current management strategies appear to be insufficient in managing the risks. The struggles of farmers in an arid country is expected under the climatic change dynamics, but the provision ofsolutions by the government is limited, especially for human wildlife conflicts. Thus, leaving thesemi-nomadic Himba people to continue being vulnerable to riskswith no feasible solutions at the moment. This begs the question of whether the nomadic way of living has a chance of surviving under the changing climate in dryland countries such as Namibia.