Composition, structure, and historical development of northern red oak stands along an edaphic gradient in north-central Wisconsin

Forty-six relatively undisturbed Quercus rubra stands were surveyed. DCA and overstory importance values were used to separate stands into 4 groups: Q. rubra-Acer saccharum, Q. rubra-A. rubrum-A. saccharum, Q. rubra-Q. alba-A. rubrum, and Q. rubra-A. rubrum-Betula papyrifera. Stand position along DCA axis I was significantly correlated with soil texture, which was interpreted as an edaphic gradient from rich, mesic to poorer, dry mesic sites. All groups were dominated by overstory northern red oak; however, changes in understory dominance from sugar maple to red maple occurred from mesic to dry mesic groups. Moreover, basal area and age decreased and shrub cover increased from mesic to dry mesic groups. Historical data suggest that northern red oak was relatively unimportant in presettlement forests in the area, with the exception of transitional dry mesic sites. Most of north-central Wisconsin was completely logged and physical evidence of fire was found within or near 2/3 of the stands surveyed. These disturbances are thought to have created conditions favorable for northern red oak establishment, leading to its increased dominance in the region. Northern red oak were consistently the oldest and largest individuals in all stands and formed an even-aged canopy. Substantial northern red oak recruitment into the tree size class seemed to last for only 25-30 yr after disturbance (probably until canopy closure), after which only shade-tolerant species were successful in the understory. Under today's low disturbance regime, northern red oak may be restricted to a single generation with a strong likelihood of being replaced by sugar maple on mesic sites, a combination of sugar and red maple on transitional sites and red maple on dry mesic sites. -from Authors