An assessment of the nutrient status of sugar maple in Ontario: indications of phosphorus limitation.

Soil acidification, caused by elevated anthropogenic deposition, has led to concerns over nutrient imbalances in Ontario's sugar maple (Acer saccharum Marsh.) forests. In this study, soil chemistry, foliar chemistry, crown condition, and tree growth were measured at 36 sugar maple stands that included acidic (pH < 4.4), moderately acidic (4.4 ≤ pH < 5.4), and non-acidic (pH ≥ 5.4) soil groups. Acidic sites had significantly lower foliar P, Ca, and Mg concentrations, and the Diagnosis and Recommendation Integrated System indicated that P, rather than Ca or Mg, was the most limiting nutrient. This is in spite of widespread reports of net Ca losses from acidified soils. Mass balance studies in the region indicate that in acidic forest soils, P input from deposition is greater than stream export. Low foliar P is therefore most likely due to low P availability to trees resulting from accumulation in organic matter/biomass and/or adsorption to Fe and Al hydroxides which are more prevalent in acidic soils. Despite differences in foliar nutrition, there were no significant differences in crown condition or tree growth across the study region, suggesting that low P availability is not yet having a widespread detrimental effect on tree health.