Seasonal variation in phenolics in several savanna tree species in Botswana

Total phenolics (50% methanol) in leaves, flowers, pods and seeds of 10 tree species, Acacia burkei, A. erubescens, A. fleckii, A. karroo, A. mellifera, A. nilotica, A. robusta, A. tortilis, Dichrostachys cinerea and Terminalia sericea were investigated over one year. In all species the concentration of phenolic substances was high in young leaves, in immature fruits and seeds and low in mature leaves and pods. The decrease in phenolic concentration during the year occurred in waves, which may be related to climatic factors. Monomeric phenolics made up a high percentage of water-soluble phenolics, which was significantly correlated with total phenolics. There was a general tendency for a positive correlation between high concentrations of nitrogen, phosphorus and potassium and high concentrations of phenolics. Results are discussed in relation to herbivory and the hypothesis of a carbon-nutrient balance.