Effects of root competition on development of chestnut and oak regeneration following midstory removal

Abstract

Partial canopy cover promotes regeneration of many ecologically and/or economically favoured tree species in temperate mesic forests. However, the specific effects of belowground resource competition from different canopystratainthesesystemsarepoorlyunderstood.ThisisparticularlythecaseforAmericanchestnut(Castanea dentata (Marsh.) Borkh.), a formerly dominant forest tree species in eastern North America that was functionally extirpated from the canopy byan exotic blight disease and for which there is now increased interest in forest restoration using blight-resistant backcross hybrids. We examined the influence of overstory and herbaceous root competition (via trenching or weeding) on growth and survival of 3-year-old, underplanted American chestnut and northern red oak (Quercus rubra L.) seedlings following midstory removal. Leaf physiology was evaluated on American chestnut throughout the third growing season. Compared with northern red oak, American chestnut had greaterrelative aboveground growth and its relative growth was more responsive to theremovalof overstory root competition. American chestnut had greater instantaneous water use efficiency in the absence of overstory root competition. Herbaceous root competition had no effect on seedling growth of either species. Thus, in lowlight conditions typical of an incomplete canopy, overstory root competition and not herbaceous competition limited American chestnut seedling growth and physiological development during establishment.