Interactions among Kalmia angustifolia, soil characteristics, and the growth and nutrition of black spruce seedlings in two boreal Newfoundland plantations of contrasting fertility

To determine the nature of the negative influence of Kalmia angustifolia L. on black spruce (Picea mariana (Mill.) BSP) seedling growth and foliar nutrient concentrations, the effect of proximity to Kalmia on spruce seedlings was studied on two Kalmia-dominated sites of contrasting soil characteristics in central Newfoundland. Spruce seedlings and the soil at the base of their stems were sampled, and spruce leader length and foliar N and P concentration, as well as various physicochemical soil characteristics, were determined. Path analysis was used to determine the strength of direct and indirect relationships among variables hypothesized to be causally linked. Path diagrams were generated based on current knowledge of nutrient cycling in boreal ecosystems and mechanisms previously hypothesized to account for the influence of Kalmia on black spruce. On the wetter and richer site, proximity to Kalmia was associated with reduced spruce growth and humus extractable NH 4 -N, suggesting nutrient competition. On the drier and poorer site, results were consistent with a direct negative effect of Kalmia on the N nutrition of spruce. On both sites, we also found evidence for a direct effect of Kalmia on spruce growth that is consistent with allelopathic effects on spruce function.