In a randomized block experiment, NPKCa fertilizers were applied annually for 5 years to a mature sugar maple (Acer saccharumMarsh.) woodlot in southern Ontario. Trees selected from 3 crown classes were fitted with dendrometer bands, tapped for sap and analyzed for foliar starch and nutrients and sap nutrients. Crown classes responded differently to the fertilizers. Trees which responded significantly in diameter growth did not respond the most in sugar yield. Effects of the fertilizer treatments on sugar yield were shown to be significant when the area of crown overlap of competing trees was subtracted from the crown area of crop trees. Foliar analysis and DRIS showed which nutrients were in demand after fertilizer applications. Sap analysis showed significant relations between sap nutrients and between sap nutrients and diameter growth. Starch analysis showed significantly higher foliar starch concentrations after potassium fertilization than after other fertilizer treatments.