The objectives were to characterise: (1) the extent of variation in foliar gas exchange and instantaneous water use efficiency between trees with contrasting leafing phenologies; (2) the influence of leaf age and available soil moisture on gas exchange and WUEi of trees; and (3) chlorophyll and foliar nitrogen (N) concentrations and gas exchange parameters for maize in agroforestry and sole crop systems. Foliar chlorophyll and N concentrations, assimilation (A) and transpiration rate (E) were much greater in P. fortunei than in A. acuminata or G. robusta. A, E and WUEi were greatest in young mature leaves of all three species but declined as they senesced