A new approach to modelling streamflow reductions resulting from commercial afforestation in South Africa: scientific paper

The Department of Water Affairs and Forestry has, for some time, needed a comprehensive tool to incorporate the impacts of commercial afforestation on water resources into water use isation and allocation processes. Simulation modelling on a national scale, using the ACRU model, was identified as one possible solution. However, in order to establish confidence in the national simulation results, it was necessary to first verify model output against reliable observed data from process studies and long-term catchment afforestation experiments. In the verification phase, long term reductions in streamflow resulting from afforestation were satisfactorily simulated for five research catchments. Some problems were experienced with catchments in the Western Cape, with verifications on shorter duration experiments and the simulation of specific evaporative processes. Modelling of low flows was less successful than for total flows. In the second phase (the generation of the national database), simulations were first performed for the dominant Acocks (1988) veld type (i.e. 0% afforestation) within 843 Quaternary Catchments exhibiting afforestation potential (to determine baseline streamflow), followed by simulations of streamflow after 100% afforestation with eucalyptus, pine and wattle respectively. The difference between the unafforested and afforested simulations equated to streamflow reduction caused by afforestation. This culminated in the generation of maps and tables expressing reductions in streamflow per Quaternary Catchment, which represents a working solution for immediate application but may be improved upon with further work. Southern African Forestry Journal No.196, 2003: 27-3

Using life strategies to explore the vulnerability of ecosystem services to invasion by alien plants

Invasive plants can have different effects of ecosystem functioning and on the provision of ecosystem services, from strongly deleterious impacts to positive effects. The nature and intensity of such effects will depend on the service and ecosystem being considered, but also on features of life strategies of invaders that influence their invasiveness as well as their influence of key processes of receiving ecosystems. To address the combined effect of these various factors we developed a robust and efficient methodological framework that allows to identify areas of possible conflict between ecosystem services and alien invasive plants, considering interactions between landscape invasibility and species invasiveness. Our framework combines the statistical robustness of multi-model inference, efficient techniques to map ecosystem services, and life strategies as a functional link between invasion, functional changes and potential provision of services by invaded ecosystems. The framework was applied to a test region in Portugal, for which we could successfully predict the current patterns of plant invasion, of ecosystem service provision, and finally of probable conflict (expressing concern for negative impacts, and value for positive impacts on services) between alien species richness (total and per plant life strategy) and the potential provision of selected services. Potential conflicts were identified for all combinations of plant strategy and ecosystem service, with an emphasis for those concerning conflicts with carbon sequestration, water regulation and wood production. Lower levels of conflict were obtained between invasive plant strategies and the habitat for biodiversity supporting service. The added value of the proposed framework in the context of landscape management and planning is discussed in perspective of anticipation of conflicts, mitigation of negative impacts, and potentiation of positive effects of plant invasions on ecosystems and their services