Soils in a hemlock-hardwood ecosystem mosaic in the Southern Lake Superior Uplands

One of the hypotheses explaining the complex mosaic of forest cover types in the Southern Superior Uplands is soil diversity. However, the distribution of soil taxa was comparable in 37 old-growth and managed northern hardwood and hemlock (Tsuga canadensis (L.) Carriere) stands. Moreover, analysis of variance revealed no significant differences in basal area, effective rooting depth, forest floor mass, and diagnostic soil horizon thicknesses between the two cover types. However, the amounts of exchangeable Ca, Mg, K, and the sum of bases were significantly greater in the upper 40 cm of mineral soil beneath hemlock than beneath northern hardwoods. These differences were accompanied by a greater amount of base cations, particularly Ca, in aboveground biomass of old-growth northern hardwoods than old-growth hemlock. A large pool of base cations exists in the lower sequum of bisequal soils composing about half of the soils of the region, but tree roots may be unable to exploit these nutrients because of a dense fragipan. There were no significant differences in soil nutrient pools in old-growth and managed stands of northern hardwoods.