Ground layer competition and herbivory effects on cherrybark oak (Quercus pagoda Raf.) regeneration in experimental canopy gaps1

Abstract

COLLINS, BEVERLY (Savannah River Ecology Laboratory, Aiken, SC 29802). Ground layer competition and herbivory effects on cherrybark oak (Quercus pagoda Raf.) regeneration in experimental canopy gaps. J. Torrey Bot. Soc. 130:147-157. 2003. -Windthrows and small-scale forest harvests generate environmental heterogeneity and dense regrowth. In such sites, interactions among environmental factors, competition with ground layer vegetation, and herbivores attracted to the disturbed area all potentially influence recruitment and early establishment of canopy tree species. I examined the interactive effects of overstory gap size, canopy openness, herb layer competition, and mammalian (deer, swamp rabbits) herbivory on emergence and seedling bank formation of cherrybark oak, Quercus pagoda Raf., in experimental gaps created by mechanized logging in a bottomland hardwood forest. Acorns were planted in exclosures (deer, swamp rabbits, deer + swamp rabbits, neither) in the center of three gaps of each of six gap sizes (7, 10, 14, 20, 29, 40 m radius) and outside the exclosures in center, edge, and forest positions. Mortality was greatest during recruitment (within the first season), and was due primarily to damage to acorns by seed predators and shade effects on seedling establishment. After three seasons, seedlings from damaged acorns in the exclosure plots were shorter than those from undamaged acorns; however, these seedlings had higher relative growth rate, which suggests that acorn damage effects decline over time. Herb layer competition and shade due to position within a gap or gap size were associated with reduced survival or height of seedlings, both in the exclosures and in center, edge, and forest positions. Deer or rabbit herbivory had no measurable effect on seedling survival or growth over the first three seasons. Natural or created canopy gaps ' 14 m radius can be foci for Q. pagoda regeneration if acorns are protected from predators; however, the dense vegetation in regenerating gaps could limit seedling height growth and multiple openings may be necessary for ascent out of the seedling bank.