POSSIBLE INTERFERENCE OF FERTILIZATION IN THE NATURAL RECOVERY OF A DECLINING SUGAR MAPLE STAND IN SOUTHERN QUEBEC

A five year study was conducted in a 100-120 year old even-aged sugar maple stand in southern Quebec (46 degrees 07'N 73 degrees 56'W; 305 m altitude) to explore the effect of different fertilization formulatio ns aimed at 1) correcting the most common nutrient deficiencies observ ed in declining maple stands (K and Mg), 2) decreasing soil acidity, a nd 3) simulating enrichment with atmospheric N. Seven fertilizer mixtu res were applied in the spring of 1987: 400 kg ha(-1) of K2SO4, CaCO3, CaMg(CO3)(2), (NH4)(2)SO4, complete fertilizer (''Maplegro'') and 800 kg ha(-1) of an equal mixture of K2SO4 + CaCO3 or K2SO4 + CaMg(CO3)(2 ). The site was divided into twenty-four 25 x 25 m plots and treatment s including control were replicated three times. Leaves and soils (org anic and mineral) were sampled in 1987, 1988 and 1991. Trees were core d at 1.2 m to measure their response in diameter growth. The applicati on of K2SO4 + CaMg(CO3)(2) was the only treatment that significantly i ncreased (+13%) the average growth rate over the five year period afte r fertilization. The application of(NH4)(2)SO4, ''Maplegro'' CaMg(CO3) (2) and K2SO4 reduced growth relative to the control for the five year period by 29, 24, 20 and 12 %, respectively. Positive and negative ef fects on growth can be explained mainly in terms of changes in leaf K. Both the application of Maplegro and (NH4)(2)SO4 increased soil P ava ilability. Overall, the rate of growth showed a cubic pattern of chang e over the 5 year period with peaks in 1988 and 1991. Trees in control plots went from a limiting foliar status of Ca and Mg, and surplus N in 1987 to a surplus of Ca and Mg, and lower N concentration in 1991. Our results suggest that nutrient deficiencies observed at our site we re associated with a disturbance of the biogeochemical cycle of nutrie nts rather than soil nutrient depletion.