Vigor and Nutrition vs. Sap Sugar Concentration in Sugar Maples Timothy R. Wilmot and Philip W. Brett, Proctor Maple Research Center, University of Vermont, P.O. Box 233, Underhill Center, VT 05490; and Melvin T. Tyree, Proctor Maple Research Center, University of Vermont, P. O. Box 233, Underhill Center' VT 05490 and Aiken Forestry Sciences Laboratory, USDA Forest Service, P.O. Box 968, Burlington, VT 05403 ABSTRACT. Although maple dieback has received considerable recent attention in the Northeast, little has been reported about the relationship between sap sugar yield and crown health or crown nutrition. We measured sap sugar concentration (sweetness) in six northern Vermont maple stands in the springs of 1990 - 1992, and sap volume yield from tapholes at one stand in 1991. The stands differed in average crown dieback, canopy transparency, density, and mean dbh, as well as cation exchange capacity (CEC) of upper soil horizons. Sweetness of individual trees was correlated with sweetness measured the previous year (r > 0.72, P < 0.001) and with dbh (r > 0.45, P < 0.001), but correlations between sweetness and crown dieback or canopy transparency were low (r < 0.14). Sap volume was negatively correlated with crown dieback (r = - 0.51, P = < 0.001). Possible explanations for these findings are discussed. Foliar nutrient status of trees was not well correlated with sap sweetness (r < 0.30). Affects of soil amendments, primarily cations, on sap sugar concentration were studied at three stands with low CEC. There were no treatment-dependent changes in sap sweetness 2 yr after the first fertilizer application. North. J. Appl. For. 12(4):156- 162. Although the variable nature of 'sap sugar yield from a random selection of sugar maples is well documented (Jones et al. 1903, Taylor 1956, Blum and Gibbs 1968), there is considerable uncertainty regarding the sources of this vari - ability. Anatomical differences among trees relating to starch storage capacity (Morselli et al. 1978, Wall ner and Gregory 1980) apparently account for a minor portion of the observed variability in sap sugar concentration (sweetness). Crown size and light interception have long been linked to pheno - typical differences in sap sugar concentration (Moore et al. 1 951, Morrow 1955, Blum 1971) although the relationship has never proved robust. Recent studies of the effects of early and late season defoliation (Gregory and Wargo 1986, Kolb et al. 1992) have shown little difference in sweetness between undefoliated and defoliated trees, implying that short -term differences in leaf area may not be well correlated with sweetness. Reports of sugar maple decline in the northeastern U.S. and Canada during the past decade (McLaughlin et al. 1985, Vogelmann et al. 1985, Bernie r et al. 1989, Millers et al. 1989) have heightened the concern of syrup producers for the loss of production due to tree mortality; but little has been reported recently concerning the relationship between tree health and sugar yield. Associated with the recent reports of Note: This work was made possible by USDA special grant No. 89 - 34157-4366. 156 NJAF 12(4) 1995 maple decline have been numerous reports of soil and foliar nutrient deficiencies in sugarbushes (Bernier and Brazeau 1988a, Bernier and Brazeau 1988b, Adams and Hutchinson 1992). Programs of fertilization to restore the health of nutrient deficient stands have been underway for several years (Hendershot 1991, Ouimet and Fortin 1992); these studies have focused on crown condition, foliar nutrition, and radial growth, while the effects of nutrient deficiencies on sap characteristics have not been explored. The first objective of this study was to document sap sugar concentrations and sap volume yield among trees that dif- fered in a number of physical characteristics, including crown dieback and canopy transparency. Tree - to-tree vari - ability in the efficiency of sugar production, storage, and exudation may ultimately control a great deal of the variabil ity of sap sugar yield . Nevertheless, the association between sugar yield and identifiable physical traits that may be linked to these mechanisms is important from a perspective of management for syrup production. Our second objective was to examine the relationship between sap sugar concentration and tree nutrient status, and to determine whether certain soil nutrient amendments, primarily cations, would increase sap sugar. As the concentration of sap sugar is of considerable economic importance to syrup producers, information concerning possible response to fertilizer should be useful in decisions concerning forest management.