Northern dry-mesic forest is typically found on irregular glacial topography (e.g., heads-of-outwash, tunnel channel deposits) or in areas with mixed glacial features (e.g., pitted outwash interspersed with remnant moraines). Soils are loamy sands or sands, and less commonly, sandy loams, although some are in areas where bedrock is close to the surface. Eastern white pine (Pinus alba) and red pine (Pinus resinosa) are typically dominant, sometimes mixed with northern red oak (Quercus rubra), red maple (Acer rubrum), and occasionally, sugar maple (Acer saccharum). Paper birch (Betula papyrifera), trembling aspen (Populus tremuloides), and big-toothed aspen (Populus grandidentata) can also be present. Common understory shrubs include hazelnuts (Corylus spp.) and blueberries (Vaccinium angustifolium and V. myrtilloides), as well as low-growing species such as wintergreen (Gaultheria procumbens) and partridge-berry (Mitchella repens). Among the dominant herbs are wild sarsaparilla (Aralia nudicaulis), Canada mayflower (Maianthemum canadense), and cow-wheat (Melampyrum lineare). Areas of northern dry-mesic forest that were historically dominated by red and white pines (Pinus resinosa and P. strobus) were considered the great "pineries" before the cutover. Today, the extent of red and white pine is greatly decreased, while red maple (Acer rubrum), sugar maple (Acer saccharum), aspen (Populus spp.), and oaks (Quercus spp.) have increased. Historically, fire disturbance of low to moderate intensity and frequency was key to maintaining northern dry-mesic forests.
Three different seral stages are described for northern dry forest, based on the progressive stages of forest regeneration following harvesting or a major natural disturbance from young forest to mid-seral to the attainment of reference conditions as seen in a mature stand. Stands with more than 50% aspen by basal area fall into the aspen-birch habitat type. For stands dominated by planted conifers, refer to the conifer plantation type.
- Northern dry-mesic forest--late seral: Late-seral (may also be referred to as old, old growth or reference condition) northern dry-mesic forests are dominated by trees 12" or more dbh and are usually characterized by a two-staged or uneven age canopy structure. Remnant stands that were not logged during the cutover may have trees commonly over 24" dbh, with scattered individuals up to 48" dbh or more. Mature trees include white pine (Pinus strobus), northern red oak (Quercus rubra), and red pine (Pinus resinosa), especially on certain landscapes. Mature red maple (Acer rubrum), paper birch (Betula papyrifera), and aspen (Populus spp.) may be present as well. A subcanopy of shade-tolerant saplings is often present, including white pine, red maple, and occasionally balsam fir (Abies balsamea). The forest is maintained by fire of low to moderate intensity and frequency, or by various silvicultural thinning techniques [e.g., see Landscape Considerations sections of the red pine and oak WDNR Silvicultural Handbook]. Structural diversity is higher with more snags and cavity trees contributing significant habitat for SGCN. Coarse woody debris may also be present if not consumed by periodic fire. Large conifers are an important component for many SGCN, providing thermal cover, nest and den sites, nesting material, as well as snags and coarse woody debris. Even if recognized as late-seral, most trees in managed timber stands won't reach their maximum size and age. Size and age variability are strong contributors to the value of late-seral state forests as habitat for SGCN. Multiple age structures, as well as the snags and coarse woody debris that develop as forests grow older are key for many forest-dependent SGCN. Where managed for ecological values, green tree retention and planning for and retaining snags and coarse woody debris is crucial for maintaining and promoting SGCN habitat. Important site-level characteristics that benefit SGCN include large conifers for use as nest trees (e.g. for Northern Goshawk and Red-shouldered Hawk), standing live and dead trees, an abundance of decaying coarse woody debris, and a diverse understory (e.g., for northern flying squirrel).
- Northern dry-mesic forest--mid-seral: Mid-seral northern dry-mesic forests are dominated by trees 5-11" dbh. Red maple (Acer rubrum), northern red oak (Quercus rubra), or white pine (Pinus strobus) may be dominant, while aspen (Populus spp.) and birch (Betula spp.) may be present in small patches, especially in forests specifically managed to promote them. Red pine may be present on certain landscapes. Structural complexity is slightly higher than in young forests with multiple age classes starting to develop, but not as complex as older stands. Snags and coarse woody debris are typically sparse unless intentionally retained by previous management. Nonetheless they are important for wildlife habitat. Important site-level characteristics that benefit SGCN include conifer-dominated woodlands adjacent to aquatic habitats like ponds, lakes, and streams (e.g., for silver-haired bat), and pockets of open sandy habitat utilized by several rare plants and for basking and nesting by wood turtles and slender glass lizards.
- Northern dry-mesic--young seral: Young-seral northern dry-mesic forests are dominated by trees 0-5" in dbh. They typically originate from stand-replacing events such as clear-cutting, catastrophic blow-down, or stand-replacing fire. Species can include red maple (Acer rubrum), red oak (Quercus rubra), and white pine (Pinus strobus). Red pine (Pinus resinosa) is characteristic and locally important, but its presence and abundance is dependent on seed source and landscape factors. In addition, aspen and birch can be a significant component. Structural diversity is typically low, as stands are young and usually even-aged. Snags and coarse woody debris may or may not be present depending on stand origin and recent management history. However, widely scattered large trees remaining from natural disturbance or left as reserves in managed forests may be present and significantly add to the habitat value for SGCN. Important site-level characteristics that benefit SGCN include widely spaced mature trees over a low dense layer of shrubs or small trees (e.g., for Whip-poor-will), young forest adjacent to patches of older forest for foraging, and pockets of open sandy habitat utilized by several rare plants and for basking and nesting by wood turtles and slender glass lizards.
In describing these stages, it is recognized that they exist and persist on the landscape due to a marked range of conditions depending on conservation or production goals and the nature and intensity of management. Even the most basic actions of promoting natural regeneration carry the weight of this reality. In an area where the purpose is strictly forest production, the decision to rotate and replant may be relatively straightforward, but on a site managed all or in part for ecological values the prescription and stand rotation is more complex.
