Regeneration of Northern Red Oak: Positive and Negative Effects of Competitor Removal

Abstract

The decreased ability of northern red oak (Quercus rubra) to regenerate throughout its range in the eastern United States has important ecological and economic implications. We studied regeneration of northern red oak in oak and pine stands on moderately productive sites in northern Lower Michigan. Our objectives were (1) to investigate the hypothesis that regeneration of northern red oak is more successful in pine than in oak stands and (2) to test whether removal of potential overstory and understory competitors increases regeneration success on moderately productive sites. Northern red oak acorns and 2‐yr‐old nursery seedlings were planted in spring 1991 in three natural oak stands and three red pine (Pinus resinosa) plantations on comparable, moderately productive sites. Each stand contained four canopy cover treatments: clearcut, 25% cover (50% the first year), 75% cover, and uncut. Each canopy cover treatment contained four understory treatments: herb‐layer removal, shrub‐layer removal, litter removal, and control. Seedling survival, 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 lower in the pine than in the oak stands; the pine stands had a higher incidence of white‐tailed deer browsing and lower levels of belowground resources than the oak stands. Canopy cover treatments produced a gradient from high stress (low light and soil moisture) and low disturbance (slight browsing and frost damage) in uncut plots to low stress (high light and soil moisture) and high disturbance (high browsing and frost 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 growth, the mortality of seedlings planted in uncut plots was low. In contrast, mortality was high and surviving seedlings exhibited good growth in clearcuts. Understory treatment effects were slight compared with overstory treatment effects. Results on our sites (1) do not support the hypothesis that regeneration success of northern red oak may be greater in pine than in oak stands and (2) indicate that the positive effects of removing potential competitors on seedling growth and physiological status may be compromised by simultaneous negative effects of browsing and frost damage.

Additive and nonadditive effects of herbivory and competition on tree seedling mortality, growth, and allocation

“…However, field studies of competition can be complicated by the presence of herbivores within the system (Reader, 1992;Hulme, 1996;Reader and Bonser, 1998). By altering the competitive environment, researchers may also alter the amount of herbivory experienced by a plant (Reader, 1992;Burger and Louda, 1995;Buckley, Sharik, and Isebrands, 1998). Because of these potential field complications, greenhouse studies may be the only way to effectively determine the individual and combined effects of herbivory and competition on plant recruitment and growth where herbivore removal is not practicable.…”

Successful under-planting of red oak and black cherry in early-successional deciduous shelterwoods of North America

“…Lorimer et al [35] observed that the density of the intermediate layer of vegetation negatively affected the growth and survival of oak seedlings, while understory vegetation competition had no effect. Others found similar results, namely the predominant effect of competition produced by the overstory canopy on that of the lower vegetation layer [1,11,15,48]. Grassi and Giannini [19] found strong growth and morphological relations with available light (canopy induced), but none with competing sapling's density.…”

“…Three studies have reported that decreased stand density, which would have the effect of making planted trees more visible, resulted in greater deer herbivory [11,18,51]. For two of these studies, however, that of Gordon et al [18] and of Truax et al [51], the determining factor was the understory vegetation, more than the overall openness of the stand.…”

“…It is hypothesized that herbivory, in addition to damages caused by climatic conditions, will increase with the thinning of the stand, whereas a denser shelterwood would better protect the planted trees [11,18].…”

Observations on natural regeneration in grazed Holm oak stands in the Ogliastra province (Sardinia, Italy)

“…Importanti diven gono in questa fase anche i fenomeni di competizio ne intraspecifica fra cespuglio e semenzale per luce, acqua e nutrienti che, secondo alcuni autori, si tradu cono in un minore accrescimento delle specie arbo ree (Buckley et al 1998, Rousset & Lepart 2000.…”