Responses of Understory Tree Seedlings to Trenching

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Abstract
The relative importance of aboveground and belowground competition to growth and establishment of understory tree seedlings was examined in the Piedmont region of North Carolina [USA]. First-year seedlings of three species- red maple (Acer rubrum L.), flowering dogwood (Cornyus florida L.) and sourwood (Oxydendrum arboreum (L.) DC]- were grown in trenched and untrenched plots under a forest canopy and within a windthrow. Survival and changes in height and leaf area were recorded. Nearly all maple seedlings survived. Those in windthrow plots were significantly larger than those in forest plots. Trenching had little significant effect on maple. Dogwood mortality was greater in untrenched than in trenched plots. Light (as estimated by canopy photographs) was significantly correlated with dogwood seedling size only in trenched plots. Availability of soil resources, especially water, moderated the positive effect of decreased aboveground competition. Although all sourwood seedlings eventually died, those within the windthrow survived longer than those within the forest. Seedlings of this species are extremely scarce and apparently require both high light and mineral soil for successful establishment.