Kanisios Mukwashi

On June 1st 2021, Kanisios Mukwashi successfully completed his doctoral thesis "Explaining temporal variability of and quantifying the impact of livestock grazing intensity on carbon and energy exchange in semi-arid near-natural and managed savanna ecosystems in South Africa" in the doctoral program "Ecology and Environmental Research" at the Bayreuth Graduate School for Mathematics and Natural Sciences (BayNat) at the University of Bayreuth. The work on the dissertation topic was carried out as part of the BMBF-funded research project ARS AfricaE (Adaptive Resilience in Southern African Ecosystems) and received additional funding from the German Academic Exchange Service (DAAD).

The aim of the work was the investigation of differently used savanna ecosystems in southern Africa with regard to the storage and emission potential of CO₂. For this purpose, data from two newly established sites and an existing observation tower were used and analyzed together with land use information.

One focus of the study was the determination of the net CO₂ exchange between a semi-arid dwarf shrub ecosystem (Nama-Karoo) in the Eastern Cape Province in South Africa and the atmosphere. Using micrometeorological measurements, it was possible to show that the amount and distribution of precipitation have a considerable influence on whether this type of land use represents a net source or a net sink at the end of an observation year. Another effect is shown by the intensity of grazing. A distinction must be made between sustainable, moderate animal numbers and historical overgrazing with temporarily suspended grazing.

Another aspect dealt with the question of how long the Karoo ecosystems at the beginning of the growing season need - when the first rains kick in - to develop from a net source to a net sink. Here, threshold values for the distribution and total amount of precipitation could be provided, which represent important input variables for process-oriented models. In addition, the measurement data was used to describe how efficiently the plants use the water in relation to their carbon sequestration.

The doctoral thesis provides important insights into the functioning of South African ecosystems, which cover large parts of the country, but which have so far been largely ignored in the establishment of long-term observation sites. The collected CO₂ budgets also represent valuable validation options for larger-scale syntheses of the carbon cycle.