Results/Conclusions First we assessed intermediate and co-dominant trees in 2004. We found that trees on Ca-addition plots had significantly greater foliar Ca concentrations, reduced crown dieback and greater basal area growth than trees on control (ambient Ca depleted) and Al-addition plots. An associated test showed that trees from Ca-addition plots experienced about twice as much wound closure in one year than trees from control and Al-addition plots. Subsequent measurements with dominant trees in 2006 confirmed that soil Ca addition increased foliar Ca levels above deficiency thresholds. However, following two additional Al applications since 2004, trees on Al-addition plots had elevated activities of two antioxidant enzymes (glutathione reductase and ascorbate peroxidase) in their leaves compared to trees from control and Ca-addition plots. Stems of trees from Al-addition plots also stored significantly less soluble sugars (fructose, sucrose, glucose and total) than trees from control and Ca-addition plots. Al treatment increased antioxidant enzyme activity and reduced stem sugar reserves even though no differences in foliar Al concentrations attributable to treatment were detected. Overall results suggest that mature sugar maples are vulnerable to Ca deficiency and Al toxicity, and that reduced carbon sequestration (growth and/or stored sugars) is one likely consequence of nutritional disruption.