Ecophysiological responses of Terminalia sericea to fire history in a semi-arid woodland savanna, central Namibia

Abstract

Woody vegetation is increasing in savanna ecosystems worldwide. Fire is frequently used as a management tool to decrease bush encroachment, but knowledge regarding the underlying leaf-level ecophysiological responses to fire history is lacking. In southern Africa, Terminalia sericea is a dominant encroaching species that resprouts readily following fires. The impact of fire on leaf-level photosynthesis, transpiration, conductance and water use efficiency was investigated using infrared gas analysis. Data were collected in three areas on the Waterberg Plateau with different fire histories (fire occurring 2, 3 and 15 years prior to sampling). Leaf-level photosynthetic rates were comparable to the relatively high rates shown by other encroaching bush species. In contrast to expectations, ecophysiological variables did not differ among plants in areas with different fire histories. However, photosynthetic rates were highly sensitive to variation in light level, suggesting that canopy structural differences may affect carbon fixation and growth rates at the whole-plant level. Encroachment by T. sericea may be facilitated, at least in part, by high leaf-level photosynthetic rates that are insensitive to long-term fire history on sandy, low-nutrient soils.