Assessment of ozone impacts on vegetation in southern Africa and directions for future research

Abstract

Levels of background ozone in Southern Africa are high enough to cause concern, as they frequently exceed the 40 ppb threshold currently adopted by the United Nations Economic Commission for Europe. They also surpass the exposure index of 3000 ppb.h, which is intended to protect crops and natural vegetation in Europe. Natural vegetation and crops in southern Africa may be tolerant of elevated ozone concentrations because of naturally high background levels, but additional anthropogenic inputs of ozone precursors may result in exceedances of ozone damage thresholds that affect vegetation. Current impact assessment policies in Europe are shifting from an exposure approach to one based on flux. If existing European methods are to be applied in southern Africa, the flux model would be the more appropriate of the two to assess likely impacts. Besides data requirements for flux modelling, the method would need to accommodate extended growing periods, locally appropriate crops such as maize, and the frequency and extent of drought periods. In southern Africa, crop production may be more greatly affected by drought, floods, and agronomic inputs but the possible deleterious effects of elevated ozone are sufficient to merit further investigation.