GROWTH AND FOLIAR NUTRIENT STATUS OF SUGAR MAPLE - INCIDENCE OF FOREST DECLINE AND REACTION TO FERTILIZATION

Typical decline symptoms have become common observations in the deciduous forest of southern Quebec. In 1988, sugar maple (Acer saccharum Marsh.) trees exhibiting various degrees of foliage loss were studied in 21 mature stands scattered throughout the province of Quebec in order to determine the impact of forest decline on the stands' growth and nutritional status. Results showed the following: (i) large variations in foliar concentrations existed between sites and sampling year, (ii) damaged trees were K deficient, (iii) stem radial growth over 5 years (1983-1988) and the 1987-1988 foliar K concentration decreased in a linear fashion as visual estimation of crown foliage loss increased, (iv) radial growth reduction averaged 27 and 54% for trees having a percentage of foliage loss of 6-25 and 25-50%, respectively. We tested the following hypothesis: improvement of foliar status by diagnostic fertilization in declining trees that have a deficiency in K leads to enhanced tree vigor that can be measured as increased stem growth. Beneficial fertilization effects occurred very rapidly, beginning in the year of treatment. Fertilization caused a 50% increase in stem radial growth compared with unfertilized trees in the 2 years following treatment application. This response was accompanied by increased foliar N, K, and Ca levels, and decreased P concentration, compared with control trees. The results suggest that poor growth and vigor of sugar maple on these sites are related to impaired foliar nutrition in K, and that a rapid revival of declining sugar maple characterized by a K deficiency can be produced in the short term by proper fertilization.