Northern Upland Forests
Before European settlement, the northern forest matrix landscape was a matrix of primary forest with mixed hardwood mesic sites and large tracts of white pine and red pine on sandier, more xeric sites. Pre-settlement disturbances were small-scale wind- or ice-driven. More than 95% of northern forests were cleared for lumber by the 1920s, although due to replanting and natural regeneration forest is once again the dominant landcover in the area, now covering approximately 70% of the area. Regenerated forests are younger and more even aged than primary forests previously occurring on the landscape.
Original PEL Results
Curtis and his colleagues ordinated northern upland forests along a mesic-xeric continuum. Mesic forests are found on deep loam soils, while xeric forests are found on often-sandy podzolic soils. White pine (Pinus strobus) and Canada mayflower (Maianthemum canadense) can be found along the entire continuum in the overstory and understory, respectively.
Mesic forests are widely distributed north of the tension zone and relatively compositionally uniform, though less so than southern mesic forests. The leading dominant of northern mesic forests is sugar maple (Acer saccharum), with hemlock (Tsuga canadensis) a strong second contender, and yellow birch (Betula alleghaniensis) and beech (Fagus grandifolia) as other hardwood dominants. White pines (Pinus strobus) are the largest trees but have low densities. The three most common groundlayer species are Canada mayflower (Maianthemum canadense), Solomon's seal (Polygonatum pubescens), and twisted-stalk (Streptopus roseus).
Xeric forests are primarily pine-dominated with associated hardwood species including red maple (Acer rubrum), trembling aspen (Populus tremuloides), and white birch (Betula papyrifera). In the groundlayer, lowbush blueberry (Vaccinium angustifolium), Canada mayflower, dwarf raspberry (Rubus pubescens), and bracken fern (Pteridium aquilinum) are common. A 'dry-mesic' forest type was also identified by Curis and his colleagues, distinguishable from more xeric forests by the absence of jack and red pine (i.e. dominated by white pine and hardwoods), with Canada mayflower, wild sarsaparilla (Aralia nudicaluis), bigleaf aster (Aster macrophyllus), and starflower (Trientalis borealis) as common groundlayer species.