Relationships between cold-induced photoinhibition of photosynthesis and winter leaf-loss were investigated for leaves of a wineberry (Aristotelia serrata J. R. Forst. and G. Forst.) tree. Previous work identified consistent differences in leaf loss between shaded and exposed parts of wineberry trees, possibly related to the adverse effects of cold temperatures and high irradiance during winter frosts. Differences in leaf temperature and irradiance between shaded and exposed parts of a wineberry canopy were quantified, together with their relationships to decline and recovery of cold-induced photoinhibition of photosynthesis (measured by the ratio of variable to maximal chlorophyll fluorescence; Fv/Fm). These data, together with measurements of leaf loss from selected shoots, were used to test the hypothesis that leaf loss is greater from open than from shaded parts of wineberry canopies, and increases with decreases in Fv/Fm following winter frosts. Fv/Fm of leaves on exposed shoots was always significantly (P<0.001) lower than leaves on shaded shoots. The absolute difference in Fv/Fm ranged from 0.11 to 0.57. Fv/Fm declined markedly following periods of freezing leaf temperatures (T1), but recovered after several days of non-freezing T1. A multiple regression model, including terms for integrated irradiance (Qi), minimum T1, T1 at the time of Fv/Fm measurements, and the value of Fv/Fm, on the previous day explained 95% of the variability in daily Fv/Fm. Leaf loss was greater from exposed shoots (0.22 leaves shoot-1 d-1) than from shaded shoots (0.07 leaves shoot-1 d-1; P<0.001) and increased following frost-induced decreases in the value of Fv/Fm. Measured rates of leaf loss from exposed shoots were significantly related to Fv/Fm measured 14 d previously (r2=0.89, P<0.01), supporting our hypothesis.