(Deutsche Beschreibung als PDF)

The increase in density of the woody savanna component is a common form of land degradation in South Africa with serious ecological and economic implications. The tree-grass ratio is determined by a range of interacting factors such as herbivory, fire and rainfall. Certain spatial and temporal combinations of these factors result in the suppression of the grass layer and promotion of woody growth. Related dynamics can be intensified by the regionally increasing atmospheric CO2-levels, which lead to competitive advantages of C3- over C4-plants. If land management does not accommodate these complex interrelated effects, savanna ecosystems loose resilience with a poorly reversible decrease in ecosystem functioning and productivity. At this stage, natural self-thinning processes as part of cyclical succession between open savanna and woody dominance are far beyond an economically feasible time horizon. Land-use practices to mitigate an increase in density of woody plants such as sophisticated spatio-temporal distribution of livestock or game, flexible stocking rates or prescribed burning may be ineffectual, and expensive chemical, mechanical or manual technologies need to be applied to control dense woody stands.

The interplay of management and savanna dynamics is still not fully understood, particularly in the context of global change. The joint research project IDESSA within the BMBF-SPACES framework aims to improve our understanding of these complex interplays, and to implement an integrative monitoring and decision-support system for the sustainable management of different savanna types in southern Africa. In consideration of different environmental and land-use contexts, the system will provide an optimal means of taking management decisions to combat or mitigate increasing densities of woody plants in changing climatic conditions, both over the long-term and on short notice in nearly real-time.

For this purpose, IDESSA follows an innovative approach that integrates local knowledge, botanical surveys, time-series of atmospheric and land-cover dynamics, spatially explicit simulation modelling and analytical database management. The integration of these heterogeneous data will be effected in a user oriented database infrastructure and scientific-workflow system. Accessible via web-based interfaces, this database and analysis system will allow scientists to manage and analyze monitoring data and scenario computations, as well as allow stakeholders to retrieve current ecosystem information and seasonal outlooks.