REGENERATION OF NORTHERN RED OAK - POSITIVE AND NEGATIVE EFFECTS OF COMPETITOR REMOVAL

The decreased ability of northern red oak (Quercus rubra) to regenerat e throughout its range in the eastern United States has important ecol ogical and economic implications. We studied regeneration of northern red oak in oak and pine stands on moderately productive sites in north ern Lower Michigan, Our objectives were (1) to investigate the hypothe sis that regeneration of northern red oak is more successful in pine t han in oak stands and (2) to test whether removal of potential oversto ry and understory competitors increases regeneration success on modera tely productive sites. Northern red oak acorns and 2-yr-old nursery se edlings were planted in spring 1991 in three natural oak stands and th ree red pine (Pinus resinosa) plantations on comparable, moderately pr oductive sites. Each stand contained four canopy cover treatments: cle arcut, 25% cover (50% the first year), 75% cover, and uncut. Each cano py cover treatment contained four understory treatments: herb-layer re moval, shrub-layer removal, litter removal, and control. Seedling surv ival, performance, and damage due to deer and late spring frosts were quantified along with vegetation characteristics, light, soil moisture , air temperature, soil temperature, and precipitation during the 1991 and 1992 growing seasons. Survival of seedlings was significantly low er in the pine than in the oak stands; the pine stands had a higher in cidence of white-tailed deer browsing and lower levels of belowground resources than the oak stands. Canopy cover treatments produced a grad ient from high stress (low light and soil moist-ire) and low disturban ce (slight browsing and frost damage) in uncut plots to low stress (hi gh light and soil moisture) and high disturbance (high browsing and fr ost damage) in clear-cut plots. Understory vegetation development and soil temperature were low in uncut plots, high in clear-cut plots, and intermediate in plots with partial overstory removal. Despite poor gr owth, the mortality of seedlings planted in uncut plots was low. In co ntrast, mortality was high and surviving seedlings exhibited good grow th in clearcuts. Understory treatment effects were slight compared wit h overstory treatment effects. Results on our sites (1) do not support the hypothesis that regeneration success of northern red oak may be g reater in pine than in oak stands and (2) indicate that the positive e ffects of removing potential competitors on seedling growth and physio logical status may be compromised by simultaneous negative effects of browsing and frost damage.