Phosphorus limitation of sugar maple growth in central Ontario

High levels of nitrogen deposition are expected to decrease the degree to which temperate forests are limited by nitrogen, and may ultimately result in limitation of tree growth by other mineral nutrients, notably phosphorus. To assess the possibility of P limitation in the Haliburton region of central Ontario, an area of high N deposition, we examined the diameter increment of undamaged, dominant, or co-dominant sugar maple (Acer saccharum Marsh.) trees in relation to concentrations of major nutrients (N, P, K, Ca, and Mg) in their root zones. Average 5-year diameter increments were positively correlated with soil pH and the concentrations of available phosphorus, potassium, and calcium in the root-zone soil. Available phosphorus alone explained over 74% of the variance in tree diameter increment, with a multiple regression analysis also showing small but significant effects of Ca and pH. The concentrations of nitrogen in soil (0.26%) and foliage (2.26%) were relatively high and measures of total and available soil N showed weak negative correlations with tree diameter increment. The results of this study suggest that sugar maple dominated hardwoods in central Ontario have moved from N limitation, typical of northern forests, to P limitation.