Community and Historical Analysis of Northern Red Oak Along a Moisture Gradient in North-Central Wisconsin
Nowacki, Gregory Jay
University of Wisconsin-Stevens Point, College of Natural Resources
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Forty-six relatively undisturbed northern red oak (Quercus rubra L.) stands in north-central Wisconsin were surveyed using the point-quarter method during the summers of 1986 and 1987. Using detrended correspondence analysis (DCA) and overstory importance values, stands were separated into four groups. Stand position along DCA axis 1 was significantly correlated with soil texture, which was interpreted as a moisture gradient from mesic to dry mesic. All groups were dominated by overstory northern red oak, however changes in understory dominance from sugar maple (Acer saccharum Marsh.) to red maple (Acer rubrum L.) occurred from mesic to dry mesic groups. Decreases in basal area and age and increases in shrub cover from mesic to dry mesic were also found. Historical data suggest that northern red oak was relatively unimportant in most presettlement forests in the area. Most of north-central Wisconsin was completely logged and physical evidence of fire was found within or near two-thirds of the stands. These disturbances are thought to have created conditions favorable for northern red oak establishment. leading to its increased frequency in the region. Age and diameter data indicated that northern red oak were consistently the oldest and largest individuals in all stands, forming an even-aged canopy. Substantial northern red oak recruitment into the tree size class seemed to last only for 25-30 years after disturbance (conceivably until canopy closure), and thereafter 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.