Estimation of coarse root biomass and nutrient content for sugar maple, jack pine, and black spruce using stem diameter at breast height

Estimates of belowground biomass and mineralomass are fundamental to understanding carbon and element cycling in forest ecosystems. At two sites, we measured coarse root (diametera >= 2 mm) biomass by diameter class and their mineralomass for sugar maple (Acer saccharum Marsh.), black spruce (Picea mariana (Mill.) BSP), and jack pine (Pinus banksiana Lamb.) trees to relate them to stem diameter at breast height (DBH). All regressions describing coarse root biomass and nutrient content as a function of stem DBH were highly significant (r(2) >= 0.89, P < 0.001). Root mineral element (N, P, K, Ca, Mg, and S) concentrations varied with tree species and root diameter class. Sugar maple roots had higher N, P, and S concentrations than the other two tree species. Black spruce had higher root Ca concentrations. Element concentrations increased consistently with the reduction of root diameter for the three studied species. We also found that the horizontal root extent of sugar maple was related to tree DBH. In conjunction with other studies, the relationship suggests that this tree species could tolerate a 10%-20% root loss but not lossesa >= 28%-34%; otherwise, sugar maple health and vigour would be compromised in the short term.